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Old 10-26-2017, 12:11 AM   #41
Greg1
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Default Re: hard starting 2001 SL1

These engines do have a knock sensor.

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Old 11-01-2017, 07:14 PM   #42
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Default Re: hard starting 2001 SL1

Thanks, I will pull out my SnapOn scanner out and see what the knock readings are...

On another new note, as I think I mentioned, fixing the fuel pressure problem, 100% solved a nearly decade old slow start that eventually led to a a very hard start, and stopped the recent lean code and ages old recurring P0410 code. :-)

I checked the freeze frame data today on the one remaining, ages old, recurring P0401 code, and was shocked to see the Freeze Frame data, 45 mph,...... LTFT +18.xx WTF?????

LTFT went from 12 to 18 after fixing the low fuel pressure???? That's nuts, I think? LTFT is long term and takes a long time to change. It should have returned to zero, unless something else is going on, but what could that be and why would it not display other codes or issues? I read that a LTFT over 12 should throw a lean code, but there is no pending or locked lean code? Interesting puzzle!!!

I need pull out my snap on and see what the current LTFT, clear the KAM memory and start over one more time and watch the path from start up to maybe 40 hrs of drive time to see where these numbers start and lock in at.

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These engines do have a knock sensor.

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Old 11-01-2017, 07:52 PM   #43
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Default Re: hard starting 2001 SL1

Positive LTFT suggests the engine's running lean hence the positive trims. Here's a definition and explanation: http://www.aa1car.com/library/what_is_fuel_trim.htm

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Old 11-01-2017, 09:54 PM   #44
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Default Re: hard starting 2001 SL1

That is exactly my point, it was running lean, WAS tripping a lean code, pretty fast after clearing codes. That led to finding the low fuel pressure, caused by a defective fuel filter pressure regulator with a totally bad check valve. It also had a +12.0 LTFT, that concurred with the low fuel pressure, lean code, and hard starting.

Right after clearing the engine KAL memory, and doing the relearn, that was super fast, I had a green code scanner light, and a nearly zero LTFT. No 410 or lean code in nearly 1000 miles, no hard starts, super fast starts now, runs great, and fuel MPG is back to about 28 mpg city.

So I am shocked that a years old, recurring 401 code (EGR valve flow) would show up with freeze frame data showing an even worse LTFT, with no other codes, or lean issues except the 401 code. If it was even leaner

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Positive LTFT suggests the engine's running lean hence the positive trims. Here's a definition and explanation: http://www.aa1car.com/library/what_is_fuel_trim.htm

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Old 11-24-2017, 06:02 PM   #45
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Default Re: hard starting 2001 SL1

Well, the plot thickens on the 401 and 410 code story. Got about 70 miles on it, and it never locked in the emis monitors, stayed with a yellow light, pending code only, no check engine light, so I cleared the codes right after a cold morning first start, cleared the codes with the scanner and the 401 code came back faster (first decel from 70 mph...) and it was rapidly repeatable. Then the 4 the time it switched to a P)410 code and no 401 code. I cleared the code just before turning the engine off, then got the barely tried to run and start thing again for 10 cranks. So I disconnected the battery this time and drained the PCM memory like last time it would not start.

It started right up, in a split second, and the scanner went all green, no codes at all (engine was warmed up by then), ready for emissions sticker testing!!!! Hmmm, that lasted for a 3-4 minute stop n go trip and then a 30 minute freeway ride. Getting off the freeway, decel the P0401 code returned, this time with a red check engine light.

STFT was flat at 0 and the LTFT was only about +4.5 this time in the freeze frame data where it threw the first P0401 code about 5 days ago. Throttle was closed at 47 mph. ECTS was at 204 F, Bank one was Open Loop (normal for decel). It took over 60 miles for it to throw that code since I disconnected the battery the first time to solve the no run-starting problem that first happened after I fixed the fuel pressure problem.

I do not think I have heard the Air blower on the emissions stuff turn on in ages. Did not turn on in ages on cold first starts of the day for weeks, maybe months now. Not that I recall hearing. I checked this morning and nothing.

Almost forget, first start up today, it was pinging very badly at 20-30% of WOT, very noticeable, but stopped after I cleared the P0401 code.

Wish I had my MT-25000 attached at the time to see the knock sense data. And any other data.

I plan to pull and clean the EGR and blow out the ERG head ports again, third time in 2 years and see if that works this time, not the fuel pressure is fixed. The EGR is new ( 1 year old). I do not have expectations, but curious what I find and if it helps this time.

The real story here is that disconnecting the battery, versus just clearing codes, has such a huge effect on it. I think the Computer is learning and saving some bad data in the KAM memory that speeds up its throwing codes, etc.

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Old 11-26-2017, 03:36 PM   #46
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Default Re: hard starting 2001 SL1

"Bank one was Open Loop (normal for decel)....." is incorrect. Cold engine startup always begins with open loop mode (engine coolant below approximately 179F and O2 sensor not heated up yet). After some minutes when the O2 sensor heats up above 600F, it sends valid signals to the PCM. Once the PCM sees O2 signals, it enters closed loop for the rest of the engine cycle. As long as exhaust keeps the O2 sensor heated up above 600F, the OBD II system remains in closed loop. If your engine was already running several minutes, it should remain in closed loop mode of emissions control and not go back to open loop at anytime including deceleration. Something triggered the system to come out of closed loop mode to revert back to open loop mode. Open loop mode usually occurs at startup where rich fuel mixtures are needed for cold engine running and would fail emissions if the engine remains in open loop mode. Basically, the emissions system waits until the engine warms up then waits for the O2 sensor to heat up above 600F. The last sensor to wait on is the O2 sensor. Until then, the PCM will not enter closed loop mode of emissions control. Any sensor not operating during normal engine running either prevents entering closed loop mode or kicks the system out of closed loop mode and reverts back to open loop mode. Resetting or battery disconnect to erase keep alive memory does the same by erasing all learned emissions parameters as if the car just came off the assembly line. All emission monitors have to learn new values as the car is driven in open loop mode until parameters are learned and fall within the range of each sensor value permanently stored in programmed memory for comparison. Once learned, falls within parameters and stored, each monitor falls into line until they all pass when closed loop mode is entered - this point means the car will pass emissions inspection and not because the check engine light turned off. A reader is needed to ensure the OBD II system displays OK or READY.

Closed loop mode does not go back to open loop mode every time the engine or car decelerates. Something is wrong.

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Old 11-26-2017, 07:49 PM   #47
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Default Re: hard starting 2001 SL1

I guess I was not clear. Everything I know and have read says that if you are cruising along, say at 40-70 mph and you take you foot off the gas (laymans language)(tech version Closed throttle, TPS at 0% open), the ECU/PCM switches to open loop during rapid deceleration. I know for a fact the 87-90 Renix Jeeps do this. IIRC it has to with making sure the NOX stay low and the engine does not lean out too much due to the closed throttle plate.

My MT-2500 reports the engine running closed loop even 1-2 second after I turn the engine on. The electric heating element in the O2 sensors are very fast at warming up the O2 sensors and I do not live in the freeze your arse off north, LOL.

My 87-90 Jeeps switch to closed loop on cold start ups in 1-2 seconds max, according to the Snap-On MT-2500 scanner. At 0% TPS, closed throttle rapid decel, the Jeeps do switch to open loop for a good 2-6 seconds until the O2 sensors see normal O2 switching across the .45 Volt threshold again. I have watched this live with the MT-2500.

I had to order a K-9 personality key for use on the Saturn 2001 this week, waiting for it to arrive late next week, as some of the data on the MT-2500 was not right using the K-2 key I have.

But the Freeze frame scanner confirmed it was in open loop when the fault code P0401 was thrown, doing about 47 mph, 2300 pm, with the TPS closed, 0% open. So that confirms that the Saturn also switches to closed loop for a moment when the throttle plate, TPS is closed.

http://www.gmtuners.com/tech/modes.htm

DECELERATION FUEL CUT-OFF

During conditions of extreme deceleration, such as what would happen if you let off the gas when the vehicle is traveling at highway speeds, a complete fuel cut-off of the engine can be commanded by the ECM to cut all emissions output. This also has the benefits of allowing the engines compression to slow down the vehicle (called engine compression braking). The ECM looks at MAP or MAF, TP, and vehicle speed to determine when to enter decel fuel cut-off mode and how long to stay in this mode. This mode overrides decel leanout mode. Instructions in the ECM programming determine when this mode is to be exited to prevent engine stalling.

ZERO FUEL SUPPLY IS NOT CLOSED LOOP!

http://www.lxforums.com/board/engine...ce-manual.html

The PCM may receive a closed throttle input from the Throttle Position Sensor (TPS) when it senses an abrupt decrease in manifold pressure. This indicates a hard deceleration (Open Loop). In response, the PCM may momentarily turn off the injectors. This helps improve fuel economy, emissions and engine braking.

Hard braking, rapid decel is exactly what is tripping is my P0401 code and nothing else.

Also I have always been led to believe that disconnecting the battery on any OBD-II rig, required one to go through a relearn drive procedure to get to the point where a scanner or State inspection OBD-II test at the test port would show a clear green light on the test scanner so that a vehicle could pass OBD-II emissions inspections, I have never seen one that could be reset disconnecting the battery with out driving it?

This Saturn is the first one I ever saw immediately go green on a code scanner with out any drive time on it just by disconnecting the battery to clear the KAM memory.

One I get the K-9 personality key I hope to learn a lot more data about what all is going on. Then I plan to pull the EGR valve and blow out the head/ports... and reinspect the entire air blower set up (P0410 code it trips once a blue moon). May need to finally pull the head to get all the carbon crap out of those tiny EGR/head/exh-manifold ports, which I hope to avoid...

I was hopping since the codes stayed away so long after replacing the FPR, that the low fuel pressure may have been part of the P0401 code issue, but alas they are back. But the higher fuel pressure did affect the frequency and time delay between clearing the codes and their returning.

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Old 11-26-2017, 09:50 PM   #48
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Default Re: hard starting 2001 SL1

While you are pointing out deceleration fuel cutoff to back up explanation for open loop mode, you're avoiding the fact that at the moment you have the error code pop up, you're confirming open loop mode. How can you base this explanation if you haven't driven a car without this error code? Its convenient to conclude your presumptions of deceleration with open loop mode but you haven't driven the same Saturn without error codes and observed whether or not a normal car without error codes remains in closed loop or not. Basing conclusions with error codes may be misleading you. I use baseline info from known good observations by logging an error free drive. From ignition on and logging info(1), startup recording cold engine running(2), warming up for another reference(3) and random speeds for other parameters(4). Without these baseline logs, I couldn't help another member determine his maf sensor failed. We were fortunate to have his logs and mine for comparison purposes. The maf sensor used in drive by wire systems display airflow volume per second. Using my idle speed baseline info, we determined his maf sensor airflow was incorrect. Replacing his sensor corrected problems. I've never used my baseline info before and it was helpful in this thread of an L300 problem. There were zero maf sensor error codes in this problem.

The O2 sensor during deceleration must remain above 600F otherwise any cooling effect of injectors being shut during deceleration will drop temps with the pcm leaving closed loop and revert to open loop. This is coincides with your explanation, if correct. In fact, this won't occur during closed throttle or during deceleration fuel cutoff. (1)Throttle is never fully closed and (2)the pcm knows via throttle position sensor signals to (a)stop fuel injector operation from speed until rpm drops back down to around 1200 when (2) injectors resume operation. When injectors are disabled during closed throttle operation, engine compression is used to help slow down a vehicle. While injectors are disabled, no fuel is injected yet spark continues. Without fuel, the exhaust has zero heat with the O2 sensor cooling off. Throttle never closes and the idle air control valve allows airflow as commanded by the pcm to continue airflow to feed the heated catcon. Cooling off below 600F won't occur because the rpm drops down quickly enough to around 1200 where injectors are enabled again. This brief period of rpm drop occurs faster than the O2 sensor dropping below 600F, allowing the EFI system to remain in closed loop. Please note that I'm discussing Saturn EFI systems only and not other EFI systems. Technical discussions requires staying within a brand and not introduce other facts from other brands that may confuse or be misleading. In the following reply, I'll try to post service manual descriptions.

O2 sensor operation; The O2S-1 is located in the exhaust manifold used by the PCM to make fuel control corrections toward a 14.7:1 air/fuel ratio. The O2S-1 is an electrical source that responds to oxygen content in the exhaust manifold. When the sensor reaches approximately 316C (600F), it produces a voltage based on the difference in oxygen between the atmosphere and exhaust gas. The PCM sends a bias voltage (391-491 mV) on the signal line which can be read on the scan tool when the sensor is cold. When the O2S-1 is cold, it produces no voltage and has extremely high internal resistance. However, when the sensor heats up, it produces voltage that overrides the bias voltage. This voltage is read by the PCM to determine a rich/lean O2S-1 signal used to adjust injector pulse width. Under normal conditions, low sensor voltage means high oxygen content/lean air-fuel mixture and vice versa. Normal sensor readings will fluctuate between 10-999 mV.

Last edited by fdryer; 11-26-2017 at 10:00 PM..

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Old 11-26-2017, 10:54 PM   #49
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Default Re: hard starting 2001 SL1

Here are reprints from the service manual.
Attached Files
File Type: pdf Fuel Controls Description.pdf (116.1 KB, 2 views)
File Type: pdf Idle Air Control Description.pdf (120.2 KB, 0 views)
File Type: pdf Fuel Controls Description-1.pdf (110.1 KB, 1 views)

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Old 11-27-2017, 06:02 PM   #50
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Default Re: hard starting 2001 SL1

Thanks for the links!!!!

From the third link you posted:

Deceleration Mode:
"The PCM responds to decreases in throttle position and manifold pressure reducing the amount of fuel. When deceleration is extended, the PCM cuts- off fuel completely when power is not needed.

Like I said zero fuel flow is not closed loop, it is open loop, and the PCM is ignoring the O2 sensor data during rapid deceleration. Mine reported a freeze frame data point of 204 F, TPS closed, vehicle at 47 mph and engine at 2300 rpm exactly when it threw the P0401 code. I had just gone from accelerating to using the brake, closed throttle at the exact moment it threw the 401 code.

Those are the conditions when the PCM would open the EGR, that code is for too little EGR gas flow.

Once I again, what I find curious is that it did not throw that code or any code for about 100 miles after I replaced the FPR and disconnected the battery under any driving conditions
.

But it did switch to a green emisisons light on my OBD-II scanner immediately after start up, with zero seconds of a drive relearn process, after I disconnected the battery.

I have never ever seen or heard of OBD-II rigs doing that, they always triggered a relearn drive requirement before they would show a green light instead of a yellow light on the scanner. The yellow light indicating the PCM is relearning the sensors and engine performance at various conditions before it goes green (OK) or red (throws a code).

"
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Here are reprints from the service manual.

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Old 11-27-2017, 06:33 PM   #51
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Default Re: hard starting 2001 SL1

I beg to differ as this part of EFI systems isn't discussed at length and I go by the presumption that closed loop mode remains throughout a normal drive without error codes. Error codes simply means the emissions self tests halt at the last error code and cannot continue until the error is corrected with a repair and automatically detected upon the next startup or drive cycle where the correct repair is detected and the emissions self tests continue. This is the easy way for error codes to reset without requiring the 'drive cycle of varied speeds in local and highway traffic, taking up to 50 miles of driving to relearn parameters and store them into keep alive memory. Disconnecting battery negative or using a reader to reset erases all emissions parameters already learned as if the car left the assembly line. To reiterate, it would be very strange for the EFI system go from closed loop mode of normal everyday driving to open loop just because we're decelerating from speed whether coasting on flat roads or down a steep hill. Closed loop remains for several reasons; throttle is never fully closed, engine rpm never drops to idle but stays above it until speed drops below approximately 5-15 mph, where the EFI system returns to fuel injection before the O2 sensor can cool off. You may not fully understand how decelerating fuel cutoff operates unless driving a manual or simply observing the tach when letting off throttle in an automatic. Try it and observe tach rpm. Rpm will never drop down to idle while coasting. The rpm drop will be so fast that fuel cutoff lasts less than approximately three seconds. Remember, I'm discussing a normally operating engine without any error codes - a normal engine run. Observing a high idle while coasting is not fuel cutoff but injection cycles. If you tried to coast all the way to zero speed, the engine is still running - fuel injection resumes at approximately 1200 rpm otherwise the dead engine in your scenario would bring the car to a stop. It ain't gonna happen.

If you insist on disconnecting battery negative or using reader reset, all you're doing is complicating diagnosing and troubleshooting without correcting anything.

Last edited by fdryer; 11-27-2017 at 06:41 PM..

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Old 11-27-2017, 07:23 PM   #52
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Default Re: hard starting 2001 SL1

Well maybe we can agree (LOL) to disagree. The terms the automotive industry is using are being used poorly since they came from my world, chemical engineering, a world of critical process control. In reality the engine runs closed loop, process control closed loop all the time, even in what Detroit calls an open loop limp mode.

What they call closed loop refers to whether or not the PCM is using O2 sensor data to modify the closed loop process. For some reason they chose to call it open loop when the PCM temporarily ignores the O2 data and shuts off the injectors.

Does not matter if it is 5 seconds, 6 months or .000005 seconds, when the PCM goes to so called open loop to shut off the injectors on decel, as the manual describes, that is what the Auto industry calls open loop, one version of it, however brief it is. The rest of the PCM, sensor and controls package continue in a second version, closed loop manner that ignores the O2 sensor data. In my world we would call them closed loop 1 and loop 2. For laymen Detroit decided to call it open loop. So lets complicate things and call it open closed loop LOL

In my experience, sometimes the only way to rapidly get a fixed rig back on the road with a green OBD-II light in 1-2 ( or as I found with this Saturn, zero seconds) minutes is to disconnect the battery and erase the KAM memory, as its memory can be so trashed as to take forever to get the rig back to normal even after fixing everything. I have experienced this with rigs that span from 1987 Renix-2001 OBD-II Jeeps, 1996 Fords, to 2001 Saturn now. I have never seen one take longer to relearn after disconnecting the battery, in fact I have seen just the opposite. I am usually just too lazy to to disconnect the battery....

But here is my point in a nut shell, it is not correct to say the thing is in closed loop when the O2 sensor data and PCM algorithms say feed X amount of fuel, and the PCM has ignored the O2 sensor date and used the TPS closed data to cut off the fuel, if even for 1 second or 1/10th of second.... during the decel process as described by the manuals.

This Saturn does and is running closed loop using a working O2 sensor and the data from different types of scanners confirms that. The only moment it shifted to open loop was the exact moment the freeze frame caught when i let of the gas and hammered the brake at 2300 rpm at 47 mph...., which forced it to finally throw a P0401 code!!!

Last edited by Ecomike; 11-27-2017 at 07:33 PM..

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Old 11-27-2017, 08:52 PM   #53
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Default Re: hard starting 2001 SL1

Our disagreement is in the information you have, possibly mixing more than one issue to presume closed loop to open loop occurs because of presuming your O2 sensor dropped out (it didn't) when its the P0401 code that's forcing open loop mode. Let's face it, can we agree the O2 sensor isn't cooling off during deceleration since exhaust temps are well over (approximately) 1400F/760C? Minimum operating temperature is 600F when O2 sensors begin outputting. Unless you're up to trying a simple deceleration run in a normal engine free of error codes, you may not fully understand why closed loop remains in this mode no matter what driving conditions are encountered. I believe your justifying your thoughts of closed loop going to open loop only on deceleration when it's more likely the P0401 error code causing it. Again, I really believe you're mixing the two, deceleration fuel cutoff and this error code into believing deceleration is causing the fuel cutoff and leaving closed loop for open loop.

Neither chemical engineer nor familiar with process control in industrial settings, I feel a familiarity with EFI systems and cannot make comments on how phraseology can be adapted to your world outside of EFI systems. I am by no means an engineer and just another diyer with familiarity of two, four stroke and diesel engine basics along with EFI systems learned over the years. A little common sense to make it understandable. Ever since America mandated emissions controls for every car and SUV, I've read as much to keep up. It helped when I already knew older distributor ignition and carburetor engines, basic electronics and EFI system in my first foreign sports car along with its service manual to explain all new sensors. Stepping from non existent sensors to a slew of them took time to absorb their interaction with a mini computer (stand alone controller?) with programming for my first introduction to EFI systems. It was bullet proof then as it is now with tweaks as refinements came along to several iterations or versions to settle on what we have now. The very best and worst example of how well EFI systems are? VW caught and fined several billion dollars with deliberately bypassing emissions programs by abusing a privilege between (I believe Bosch technical support engineering) and VW in house engineering to switch off emissions controls in normal driving mode. A simple code given to VW to use strictly for testing purposes, not for mass marketing use. VW abused the privilege, was caught inadvertently by research people in the USA logging data when they noticed an anomaly and duplicated it before informing the EPA. Once exposed, VW came clean after attempting to downplay it. Simple coding that was supposed to be used for research and testing became a bypass for emissions controls to polluting America. Cheating, plain and simple.

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Old 11-27-2017, 10:47 PM   #54
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2001 SL1
Default Re: hard starting 2001 SL1

It is not the P0401 code, nor is it the O2 sensor that is triggering open loop mode, it is the PCM seeing a sudden complete drop from a 30 % something engine load (in closed loop, with no codes) to a closed throttle that tells the PCM to follow the secondary loop protocal called open loop for a short period of time. The PCM reports it as open loop, but only for milliseconds to a few seconds at most.

Tonight I repeated similar, but not the same conditions and it went from no codes to the same P0401 code with the freeze frame reporting closed loop this time, so that time it threw the code just before or after the short open loop mode the computer is programed to do during a rapid Decel-suddenly falling from a large load cruising rpm to a closed throttle/braking condition. This time the freeze frame reported CL Closed loop at the moment the code was thrown.

Also your apparent presumption(?) from several posts... that my rig is running open loop all the time(?) or open loop after a code is thrown is not correct. Even after it throws the P0401 code it is still running closed loop, except during the brief decel or first seconds of a cold start up. I have live data showing the O2 sensor actively switching above and below the .45 V target. Open loop does not do that.

The 401 code is not causing the open loop, in fact many (most?) error codes do not disable the PCM from running closed loop. P0401 has no reason to disable the closed loop mode permanently. And running closed loop, say due to a bad O2 or CTS sensor, would not throw a P0401 code.

I agree the O2 sensor does not have time enough to get below 600 F with what I am doing this, which confirms that the PCM decel command structure I showed you multiple links to is what causes the short term switch to open loop reported in the freeze frame during rapid fast breaking from a cruising speed (like I was doing in the tests). Because the O2 sensor is not getting cold enough to force a switch to open loop.

This operating condition, seems to be the only driving condition where I can force it to throw the P0401 code, which is what I was posting about and sharing.

Also if the O2 sensor was not working, if the heater in it was bad, or the power to the electric heater in the O2 sensor was bad, the engine would not be running like a new engine at idle at high acceleration, and so on......or seeing cold (>55 F, LOL) starts going to closed loop in 1-3 seconds....

In fact I thought is just cool that the freeze frame was fast enough to catch the code being thrown when the PCM commanded open loop the same time it threw a P0401 code. The TPS, CTS, RPMs, Veh Speed, and so on on the freeze frame confirmed by virtue of all their data results that the code was thrown when I switched from accelerating (33% load at about 43 mph) to rapid breaking. I watch the light switch to red / code fired the moment I hit the brakes. Seems to be the only way I can force the 401 code to repeat. Which does make sense since decel is when the PCM is supposed to operate the EGR and recycle exhaust gas into the intake manifold to lower engine temps and avoid a too lean condition during deceleration. Also now that I think of it, when that EGR gets thrown open, and the FIs get cut off for a split second the O2 data becomes a little suspect anyway.

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Old 11-28-2017, 02:37 AM   #55
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Default Re: hard starting 2001 SL1

I may be getting knee deep into this and misinterpreting some info. As near as I can tell, open loop mode has always been with coolant temps below a certain temperature, say 170F while the O2 sensor takes it time to reach 600F before valid signals are acceptable for the pcm to use it, ultimately waiting for the O2 sensor, as described in service manuals, before entering closed loop mode. You return repeatedly with the O2 sensor almost immediately switching as soon as the engine's started. This goes against almost everything I've read that says the O2 sensor takes time before signals are generated. I can't corroborate this with actual live data observations. Is it possible your O2 sensor is faulty, working almost immediately on engine startup and then intermittently failing during deceleration/braking? Just hypothetically speaking.

I chose to use the egr valve error code to counter triggering closed loop mode to revert back to open loop. Virtually all info to date from here surrounding difficulty in leaving open loop mode to closed loop are due to faulty coolant sensors from all the S-series faulty original coolant sensors. With most sensors sending the equivalent of a frozen engine, very high resistance that would send low signals, the pcm sees a cold engine and never leaves open loop mode while every other sensor is operating correctly. Time and time again, readers displayed 'Not Ready' or other message with pending codes and failed emissions inspection. Once the coolant sensor was replaced, the correct signals were sent and when the pcm wasn't reset, the OBD I or II system went 'Ready' and passed emissions inspection. The same for a faulty O2 sensor - when found and tested for less than normal switching frequency or lower voltage than expected, the pcm refuses to leave open loop mode. O2 sensor switching frequency is rarely tested by anyone, including me, so ruling out all other sensors points to the O2 sensor and replacing it allowed an engine to leave open loop for closed loop to pass emissions inspection. Other sensors do the same to prevent the pcm from leaving open loop for closed loop.

Open loop; less than ideal stoichiometric 14.7:1 air/fuel mixtures, faulty map/coolant/tps/O2 sensors. Closed loop mode; all sensors operating within their design range to allow the pcm to run EPA mandated programmed emissions control. Any sensor that triggers a fully warmed engine running in normal closed loop mode to leave and default back to open loop mode basically points to an errant sensor. You may be the only one to prove an O2 sensor sending correct signals as soon as the engine starts up. Or its not operating as you may think. I don't know. You're the only member here that claims closed loop mode is entered soon after cold engine startup. I'm suspicious of this claim. Even my wide band O2 sensors are described as taking about a minute or more before heating up to operating temperatures and is equipped with a heater. I don't recall if my reader can refresh with a touch screen display fast enough to keep refreshing and observe open loop to closed loop in the first minute or two. I may have to try it myself to see if open loop enters closed loop in less than a minute. Be that as it may, your observations of leaving closed loop for open loop goes unanswered.

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Old 11-28-2017, 09:52 PM   #56
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2001 SL1
Default Re: hard starting 2001 SL1

Then you need to read up on and understand O2 sensor technology. Ever since 1987 on the Renix Jeeps, the O2 sensors have had 3-4 wires. The third wire is 5-14 volts feeding an electric powered resistor inside the O2 sensor that gets red hot and heats the O2 sensor on start up in seconds to over 600 F. Even in super cold climates. FWIW, I wrote the book on Jeep Cherokee, 87-01, O2 sensor testing.

As soon as the ECU/PCM sees the O2 sensor data operating normally, the computer switches to close loop. Later models also wait for the CTS to warm up before going closed loop. That temp threshold varies over the years and models. My 1987 Renix Cherokee switches to closed loop in 1-3 seconds. Same for my Saturn 2001 SL-1.

No my O2 sensor works perfectly. Open loop is an ECU/PCM decision, and it can enter open loop for many reasons, even with a working O2 sensor. In fact if the computer senses with a perfectly working O2 sensor, that engine is stuck running rich or lean for any reason, and the Computer can not get the fuel mixture to switch from rich to lean, back and forth on command to satisfy the Cata Converter needs for a slightly rich mix, the computer will switch to open loop even with a good working, hot O2 sensor and CTS sensor.

The Computers try / test their ability to run closed loop, and if they fail after several seconds they switch to open loop for a little bit, then try again, If they fail (typically 3 times to operate closed loop) they switch to open loop till the engine is restarted. I suspect the urban legend about the CTS needing to be hot enough is not s precise target CTS temp, but perhaps about failed O2 sensor internal electric heaters not getting power (bad fuse, torn wire from road hazards...etc) and taking a long time to get hot enough to work closed loop, thus the minimal CTS temps. But I have seen some OBD-II manuals claim this is some mysterious minimum CTS temp to get closed loop operation.

My 87 Jeep and 2001 Saturn both have pretty new O2 sensors (1-2 years old less than 10,000 miles) that have working electric heaters (OEM) and they both go closed loop in seconds of start up, BUT they are very well maintained vehicles with close to 300,000 miles on both.

My last 6-7 tests in a row ALL showed closed loop operation on the freeze frame when the P0401 code was thrown during rapid deceleration from the same basic conditions on all the tests.

The LTFT numbers have been all over the place, which has my attention now.

A faulty CTS telling the computer it is 30 F when it is 200F in the block, would make it almost impossible for the computer to operate closed loop due to the extreme fuel trim needed to compensate. Should throw a code, but I have seen some OBD-II rigs with a missing spark plug wire run like **** and not throw a code, LOL (Ford 1996)

MY CTS operates properly, I have read and can read the temp of the sensor live with my scanner.

On O2 sensor testing, I have an analog high impedance volt meter (old school) I can use to watch the output live.

What is tough to test for is an apparent working O2 sensor, that has some bias, but PCM LTFT should be able to handle that, compensate.

Quote:
Originally Posted by fdryer View Post
I may be getting knee deep into this and misinterpreting some info. As near as I can tell, open loop mode has always been with coolant temps below a certain temperature, say 170F while the O2 sensor takes it time to reach 600F before valid signals are acceptable for the pcm to use it, ultimately waiting for the O2 sensor, as described in service manuals, before entering closed loop mode. You return repeatedly with the O2 sensor almost immediately switching as soon as the engine's started. This goes against almost everything I've read that says the O2 sensor takes time before signals are generated. I can't corroborate this with actual live data observations. Is it possible your O2 sensor is faulty, working almost immediately on engine startup and then intermittently failing during deceleration/braking? Just hypothetically speaking.

NO.

I chose to use the egr valve error code to counter triggering closed loop mode to revert back to open loop. Virtually all info to date from here surrounding difficulty in leaving open loop mode to closed loop are due to faulty coolant sensors from all the S-series faulty original coolant sensors. With most sensors sending the equivalent of a frozen engine, very high resistance that would send low signals, the pcm sees a cold engine and never leaves open loop mode while every other sensor is operating correctly. Time and time again, readers displayed 'Not Ready' or other message with pending codes and failed emissions inspection. Once the coolant sensor was replaced, the correct signals were sent and when the pcm wasn't reset, the OBD I or II system went 'Ready' and passed emissions inspection. The same for a faulty O2 sensor - when found and tested for less than normal switching frequency or lower voltage than expected, the pcm refuses to leave open loop mode. O2 sensor switching frequency is rarely tested by anyone, including me, so ruling out all other sensors points to the O2 sensor and replacing it allowed an engine to leave open loop for closed loop to pass emissions inspection. Other sensors do the same to prevent the pcm from leaving open loop for closed loop.

Open loop; less than ideal stoichiometric 14.7:1 air/fuel mixtures, faulty map/coolant/tps/O2 sensors. Closed loop mode; all sensors operating within their design range to allow the pcm to run EPA mandated programmed emissions control. Any sensor that triggers a fully warmed engine running in normal closed loop mode to leave and default back to open loop mode basically points to an errant sensor. You may be the only one to prove an O2 sensor sending correct signals as soon as the engine starts up. Or its not operating as you may think. I don't know. You're the only member here that claims closed loop mode is entered soon after cold engine startup. I'm suspicious of this claim. Even my wide band O2 sensors are described as taking about a minute or more before heating up to operating temperatures and is equipped with a heater. I don't recall if my reader can refresh with a touch screen display fast enough to keep refreshing and observe open loop to closed loop in the first minute or two. I may have to try it myself to see if open loop enters closed loop in less than a minute. Be that as it may, your observations of leaving closed loop for open loop goes unanswered.

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Old 11-30-2017, 02:43 AM   #57
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Default Re: hard starting 2001 SL1

Debates aside, what are you left with, error code wise? And what is your warm idle rpm?

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Old 12-02-2017, 06:52 PM   #58
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Default Re: hard starting 2001 SL1

Quote:
Originally Posted by fdryer View Post
Debates aside, what are you left with, error code wise? And what is your warm idle rpm?
P0401 and P0410 have been a recurring team tag theme for years. They are not related to the title of this thread!!

The original topic of this thread is dead, fixed.

There is a long running, old thread here on the 401 and 410 code issues for many of us, and fixes for them, in another thread here. But before I yank the head of the block to fix it, I am going to go through and check for all the other causes since one of them may be back, or may have turned up finally.

Idle is perfect dead on spec. In fact the scanner says it is running +/-1% of the target RPM as the engine warms up then when fully warmed up the target is 750 rpm and it runs from 745 to 755 in a very tight band.

I used the Snap-On MT-2500 with the new to me, right personality key today and got a lot more data and access to live tests. I was able to open and close the EGR valve on command from the scanner in 10% increments, engine running in park > I was able to kill the engine at idle at one point. Started right back up at once.

In the driveway idling for 30 minutes running through all the menus and data, and cycling some tests,

It had zero miss fires on all cylinders. Knock sensor works, averaging about 40-60 knocks which is normal as I recall. The EGR does work. All the data looks great, except at idle the LTFT and SFT were bonkers, IMHO, -10 STFT and +20-LTFT, but then they went to normal, +1 to +2 on both after/during a 10 minute drive. Keep in mind I had cleared the codes (if that matters) when I started the Saturn.

One interesting thing, after I used the scanner to force open the EGR and gunned the engine a few times (maybe blew it out??? Cleaned it out), I was able to drive with out being able to force it to throw a P0401 code like I was before. This time the engine was fully warmed up, so I need to try again later on a cold start.

I need to wait a week till the 11th edition of the GM-snap-on manual arrives I just ordered, to learn all the new stuff this scanner beast can do on 2001 GM, but the tool seems to be saying it is open loop, when the O2 sensor data says clearly it is operating closed loop, as open loop O2 data is very obvious!!!!!

One cool thing I discovered today is the MT-2500 Snap-on scanner reports the actual Cat converter temperature in one of the data modes.

Now I know why the latter O2 sensors added a second ground wire!!!! The older O2 sensors, like on my 87 Jeep as 3 wires, only one ground. That fourth wire is so the ECU can sense the current going through the electric heater in the O2 sensor. The current is proportional to the Cat Converter temp!!!!
How cool (or Hot?) LOL, is that???

Cat was running from a low at 585 F at long idle to about 650 F in short acceleration bursts

Last edited by Ecomike; 12-02-2017 at 07:00 PM..

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Old 12-02-2017, 07:20 PM   #59
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2001 SL1
Default Re: hard starting 2001 SL1

Almost forgot, here is the last code scanner data set before I cleared and it and did the stuff I reported in my last post.

Freeze frame for the code P0401 CEL data

31% load
O2 sensor-ECU Closed Loop (CL)

197 F CTS

19 STFT
+18 LTFT
These 2 were the highest I ever seen them.
1378 RPM
38 MPH
Air-off
TPS 0-%

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Old 12-02-2017, 07:35 PM   #60
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Default Re: hard starting 2001 SL1

The code scanner I have lists these, or most of them anyway up top:

M - Misfire ?
F - Fuel System -?
CC - Comprehensive Component
C - Catalyst
EV - Evaporative System
2A - Sec. Air System (SAI)
O - Oxygen Sensor
OH Oxygen Sensor Heater


O, OH, C, 2-3 others, and eventually EV lock in.

I just discovered EV needs the gas tank to be between 15 and 85% full to work, LOL. That is an evap emissions test. It always seems to take forever on mine, but it is not related to the codes. I think my air blower has stopped powering up which will cause the 2A to not lock in, and eventually throws a P0410 code after many days.

But the O, OH, C and CC always lock in pass the OBD tests quickly.

Old_Nuke has said for years these two codes are carbon build up in the head and air ports, and I can confirm that as I have repeatedly cleaned those ports, and replaced all the parts involved, except the guts of the head which can not, reportedly be cleaned while the head is on the engine.

I've never been much for accepting the "it can not be done" view LOL.

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