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Old 05-16-2017, 06:09 PM   #41
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

OK.. this gonna be fun (I've been too busy to look at the car for a bit).

I just borrowed a Bluetooth-capable reader. I'll be getting the BAFX or something.
I'm using a Galaxy S3 because I now use an S4, and I wonder if the S3 can handle this stuff realtime.
I bring up update speed because I set it to show the TPS value and a couple of other things and the TPS jumped around while the engine ran (and so the software was reading and interpreting multiple streams), but moved smooth a silk while the engine was off. I had checked the connection a while back, but may have a bad TPS (I bought the car used, it could be aftermarket). There's a junkyard near me that'll remove the entire throttle body and that's at least a CHANCE that I'll get an OEM TPS.

Anyway - I'm using Torque Lite and suddenly have access to all SORTS of sensors that I don't know if my car has. Like, does my car even HAVE some kind of 'fuel trim' sensor? Or is 'fuel trim' a "here's what the PCM is TRYING to do"? I took a look and got confused. I thought it just used the upstream O2 sensor.

fdryer - I'll definitely keep an eye on the coolant temperature. What you said makes sense. I will say that the temp gage (old and new sensor) was quite happy to get up to just over , which kicks the fan on, so maybe not an issue, but I'll keep my eye on it.

The software will, apparently, be a learning experience :-)

SO, yeah, right now my biggest question is - how to I tell what sensors I SHOULD have (this software shows 2 banks with 4 O2 sensors each. Not MY car!).

Also - it shows volts at the OBD2 connector and volts at the PCM, but the "Volts at PCM" gage shows 0.. maybe my car doesn't have a way to monitor that?

Anyway - I'll get what data I can. If any of you have suggestions for which sensors I should be watching, please let me know.
I'll check the Car Diagnostic Pro - I'm guessing the $9 is to keep ads away. :-)
OK, I rambled. Sorry, between some very busy days, a sick 4 year old, and this WEIRD problem, I'm a bit scrambly. :-)

Last edited by SaturnStick; 05-16-2017 at 06:18 PM..

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Old 05-16-2017, 07:59 PM   #42
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Initial Update - Torque Lite doesn't seem to read some of the sensors. Car Diagnostic Pro didn't ask about Saturns, so I used it as best I could (I need to read the manual.. is there one?? Hmmm)

BOTH reported an Engine Load of 50% at idle. That's GOT to mean something.. but I don't know what goes into 'engine load' calculations.

Side note: the IAT was showing 122 (The engine had been off for 2 - 3 hours), so I disconnected / reconnected to see if all was well. Now it won't idle. This is the kind of things this car does to me. At last read, it was showing 80 which makes sense, I suppose - the engine and evening were warm. We'll see if it does it in the morning.

So.. 50% engine load at idle? The Diagnostic Pro had something about 'calculating airflow'.. and it made me think.. maybe my catalytic is clogged??? I wonder if I can use that airflow thing to find out....

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Old 05-16-2017, 08:41 PM   #43
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2003 L-Series 3.0L Sedan
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Well, you're on a learning curve to understand what each sensor does and when it displays info relative to coolant temps, outside temps, rpm, etc.. Engine loads are derived from all sensors so recording info and writing them on paper can help as you start reading what each sensor does and how to interpret them during live monitoring.

One sensor not understood well is the manifold absolute pressure (MAP) sensor. Its nothing more than an electronic barometer, a pressure sensor that's displayed in one of two values, inches of mercury, abbreviated as in hg or kilopascals (metric), abbreviated as kpa. As a barometer, it measures atmospheric pressure relative to sea level at ignition on time and then intake manifold vacuum when the engine's running. Map sensors are used to calculate engine load so some advanced knowledge is necessary to interpret map sensor outputs. Basically, ignition on engine off measurement should match local barometric pressure from any weather station. At warm idle, map sensor output should measure vacuum since air is always being sucked in (a naturally aspirated engine) and display somewhere between 15-21 in hg. Use a converter to convert values. Vacuum is read by a map sensor to tell the pcm relative load values (in conjunction with other sensors) - more vacuum less load, less vacuum more load. More vacuum means higher numbers where throttle is likely closed. Less vacuum would be with opening throttle to raise engine rpm, raise power. The map sensor tell the pcm how much the engine is under load as its matches data to fuel maps to determine how much fuel it needs to match engine loads. This is deep into EFI systems background info.

Other sensors displayed are just as important, relative to engine running or not. Its very useful to measure sensor output in several stages; cold engine before startup, immediately after startup and after a full warm up. These become baseline values for reference. The sensors to record baseline numbers; coolant, intake air temperature, map.

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Old 05-17-2017, 11:09 AM   #44
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

The most comprehensible description of MAP sensor operation that I've seen, and I've seen a lot! Yours makes sense and the others, I'm sure, said the same thing but with too much mumbo jumbo. :-)

My TPS checks out good in that it's smooth as silk now that I rid my phone of a bunch of useless programs.

One of the two OBD2 programs will read the intake air temp, and it seems OK, as does the coolant.

That Car Diagnostic Pro has a TON of things from what I've found. Hell, it looks like I can tell my car's EGR or IAC to move if I want. I've got to see if there's a manual for it.. if I DO have that power, I do NOT want to accidentally make it happen! :-)

So, now that I can read all of these sensors, any suggestions which might point me to why I have low power/low mpg?

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Old 05-17-2017, 03:04 PM   #45
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

You wouldn't be alone, attempting to understand live data without any knowledge of EFI systems, how sensors operate, what each does when sending signals to the PCM and how the PCM uses all signals to run the engine in every possible real world situations. I'm familiar with EFI systems since my first sports car was a first generation EFI system in a Japanese car. I was terrified and bought the factory manual so I could at least have some info on how it worked. I already know about basic two stroke, four stroke and diesel engine basics so marrying EFI to engine mechanics was one way to stay informed.

Personally, I think anyone unfamiliar with basic engine fundamentals, EFI systems and reading live data is on a steep learning curve. Unless I'm given more info, I can't determine where to look. I use baseline data gathered before engine problems while becoming familiar with scrolling thru a reader, recording data for review at any time. Having a 'map' of normal engine values allows me to compare good values against an engine with error codes if data comparison can help determine where fault lies. Not everything will be spelled out with error codes where knowing how an engine runs and how sensors operate and fail to show symptoms is all part of diagnosing and troubleshooting on a diy level. Having an expensive GM scan tool would be near perfect but that's a pipe dream.

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Old 05-17-2017, 05:50 PM   #46
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

What you said makes sense and now that I've had a look at some of it, it's kind of what I was leaning toward.. there's SO much info that, beyond "oh, look, my TPS signal jumps, maybe it's a bad TPS", I'd be doing a LOT of guesswork.

I think that I'm going to take my PCM off (it's big and near the battery.. is that hunk of metal a heat sink? OMG) and check the connection for security, give it a little more time, the take it to the shop.
We have one near work that doesn't seem bad and I have no reason to NOT trust them. I've settled myself that it could be something expensive like injectors clogged (remember, bad gas started all of this) or catalytic clog or something.
Once you've accepted that it could be the expensive option, then bringing it in isn't as painful cuz, hey, maybe they find something far less expensive. :-)

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Old 05-18-2017, 08:00 PM   #47
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Minor Update - With the scan tool in use, my idle speed jumped to 2700. Sure enough, my TPS was reading 6% with my foot not on it. This is one reason I want to check the connection and maybe grounds on my PCM - since this is the third TPS with this problem, is it the TPS or the connection?

As a side bit - This ONLY happens when my engine is hot (~50% on the gauge) and is more likely if my radiator cooling fan is on.

I'll be ordering a throttle body from a local junk yard - the body comes with IAT and TPS.

Question - since my TPS reads 6% but is actually closed, my PCM may be putting more fuel in, but does it have to open the IAC a bit as well? I mean, my throttle isn't letting much air in.....
any thoughts/ideas?

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Old 05-18-2017, 10:00 PM   #48
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2003 L-Series 3.0L Sedan
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Throttle plate position is mechanical, to set idle speed to around 500-600 rpm with the bypass air port in front of the throttle plate blocked. The bypass air port has passages to allow supplemental air around the throttle plate. This supplemental air is controlled by the idle air control valve as commanded by the pcm. When the bypass air port is unblocked, the ocm uses the iacv for all idle speed adjustments, not the throttle plate position. Read the previous description as many times until its understood. Do not try to meddle with the throttle stop screw as all you'll do is make more problems. You can block the bypass port any time after the engine is fully warmed up and verify factory set low idle. When the port is unblocked the extra air raises idle rpm to around 650-800. Any higher and either the iacv is sticking or something else is causing the intermittent high idle. Use a finger to block and unblock the bypass air port for testing.

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Old 05-19-2017, 07:10 PM   #49
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

heh.. I've known about the "Do NOT mess with that screw!" for a while. The first time I read it, I said, "OK, won't touch".
I'm a bit confused about the blocking/unblocking though.
If my throttle plate is closed and I block the bypass, how is air getting into the engine to help us get that 500-600 rpm? Does it go around the plate itself (I notice that it's not exactly a hermetic seal)?

This is just curiosity, btw.

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Old 05-19-2017, 07:56 PM   #50
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Throttle plates are never fully closed on S-series engines. If you see the throttle plate in fully closed position, this is already incorrect. No throttle is factory set at closed position.

As described previously, factory throttle plate setting is always slightly open. This allows blocking off the little bypass air port in front of the throttle plate for testing factory idle speed before testing the iacv. If throttle is completely closed, the engine will die immediately as soon as the bypass air port is blocked. This would indicate someone previously meddling with the throttle stop screw. Its not the end of the world but adjustment would have to be made to 'undo' someone else's misguided attempts to make idle speed adjustments.

All EFI systems similar to the S-series, L-series, Auras, Outlooks, Ions, and Vues (as well as many other GM vehicles using EFI systems) are all electronically controlled idle speed for every temperature condition. This simply means instant starting without touching the gas pedal in all weather conditions with a properly maintained engine. The EFI system provides automatic idle speed control and how much fuel is needed. No choke, no pressing pedal several times to force gas into the engine, no pedal needed to raise engine speed during starting - its all done by computer control.

Last edited by fdryer; 05-19-2017 at 08:03 PM..

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Old 05-23-2017, 12:59 PM   #51
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

New Throttle Body Assy - Well.. used. :-)

Thanks to Chuck & Eddie's in Connecticut, I have a brand-spanking used dirty throttle body assembly just waiting for me to clean and install it. I know not to shoot carb cleaner onto the pintle, so I'll be spraying a cloth and wiping it. :-)

I recall, in my troubleshooting, reading something about the IAC needing to be in a particular position. Someone said to reset it by doing something involving disconnecting the IACV, turning the key to run (not start), letting it stay that way for 15 seconds, reconnecting the IACV, repeating the 15 second thing, then turning the key off. After that, start the car. This is supposed to 'set' the IACV to the desired, "Just starting" position.

So, since I have read that the IAC needs to be in the right position (the manual and new IAC instructions say to make sure it's at 18mm or something), how do I get it to do that?

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Old 05-23-2017, 01:33 PM   #52
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

This may help but instructions are for using GM's scantool to power and retract the pintle before installing it into the throttle body. Try turning the pintle shaft in any direction or press it towards its housing. Another way would be powering it manually to retract it.

If the pintle doesn't allow screwing it in/out or pushing/pulling it, maybe installing it will work. Idle air control valves are commanded into position by the pcm according to engine speed, coolant temperature and other sensors. Since the EFI system relies on feedback, engine rpm from the crank sensor allows the pcm to adjust the iacv to extend (reduce high idle) or retract (increase idle) by modulating the air flow thru the bypass air port in front of the throttle plate.
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Old 05-23-2017, 04:23 PM   #53
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Excellent, thanks! I plan to do the work this Sunday. :-)

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Old 05-30-2017, 04:43 PM   #54
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Got the used throttle body in on Saturday and so far the random high idle is gone (I even tried stuff that consistently caused it). Now I can accent on the low mpg/low power problem.

Secondary - "I'm curious" question. I was digging into this problem and found a Richpin06 suggestion for testing the EGR.
Basically - you remove the EGR valve, put an aluminum sheet over the holes, and reinstall the valve. If the problem you face is reduced/eliminated, this is a pretty strong indicator that the EGR may be contributing.
Cool. Quick and easy, right?

Here's where it gets odd. I noticed, some time ago, that when I get to about 4200RPM, particularly in 4th or 5th gear, my consistently-weak engine suddenly drinks a bit of Go Juice and my power goes up sharply.
When I did the Richpin06 EGR test.. it doesn't happen at all. My engine is still weak.

It made me wonder how the EGR is supposed to operate. I know it recirculates exhaust gases to reduce the burn temperature and, with that, reduce emissions (or something like that). So, is it always open, or only when I've got the down hard or what?
I mean, PCM control seems to me to allow for varying it the way we might vary the IACV. :-)
Maybe, for some reason, when I'm climbing a hill in 4th or 5th and get to 4200RPM, my EGR shuts and doesn't reburn exhaust gases?

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Old 05-31-2017, 12:29 AM   #55
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Egr valves only operates during normal acceleration and cruise conditions. It's off at idle and wide open throttle. Adding exhaust to the intake air manifold at idle simply kills the engine and who wants exhaust gases interfering with wide open throttle?

The blocking gasket made with aluminum (soda can) is only temporary as the thin aluminum will melt. To run a test lasting more than a day, make the gasket from soup can sheet metal. If you notice zero improvement is engine performance, it's not an egr valve problem.

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Old 05-31-2017, 10:55 AM   #56
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Off at idle and full throttle, that makes sense!

Yes, I did the block thing only long enough to get both city and highway miles down and monitored my mpg with the OBD2 and Torque. Fortunately, the Torque app's average mpg gage doesn't turn off when you stop the engine, so I just drove one of my usual routes and, when I got home, checked it. Still very low.

Thanks for the info!

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Old 06-02-2017, 07:19 PM   #57
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

IACV Update - I have replaced the entire throttle body w/ TPS and IACV from Chuck & Eddies.
I still face a 'slowly drops to stall at intersections when warm' engine, I recalled BV22's suggestion about the IACV -

"Further to the good advice above, the proper way to DIY diagnose the IACV is to remove the air intake snorkel with the engine running at idle. With your thumb, cover the hole at the bottom of the throttle body, just in front of the throttle plate. Idle should drop to 450-500 rpm. Remove your thumb and the idle will jump up higher than normal and quickly settle back to normal. If this behavior is observed, chances are pretty good that the IACV is working properly."

I don't remember if I did that or not, so tonight when I got home, I did (replaced TPS and IACV with the junkyard throttle body the other day). I slid a piece of aluminum can over it. My engine died. So, I think the IACV is working in the sense that it was idling (very rough) and it died when I covered the bypass hole.

So, any thoughts?

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Old 06-02-2017, 09:57 PM   #58
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2003 L-Series 3.0L Sedan
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Read post#50 again. Someone meddled with the factory adjusted throttle stop screw. Adjust it (keep the bypass air port blocked off) until the engine idles around 500-600 rpm. When the bypass air port is unblocked, idle will jump up and then return to 650-800 rpm, the EFI system idle speed setting (warmed engine).

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Old 06-06-2017, 05:10 PM   #59
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

My brain in action: "I'm pretty darned sure this 'block the port and it dies' thing was mentioned in a previous post, so I think I'll look!" - orders eyes to look thoroughly.
2 hours later
Eyes: "Sorry, Charlie, I've looked and looked and can't find it"
fdryer: "Look at this exact, numbered post"
Brain (scowling in eyes direction): "looked and looked, huh???"
Eyes: "oooops"
Thanks. Wow, this was the new/from a junk yard throttle body.

time to have some 'fun'!

thanks for the info.
PS - I replaced the EGR as a means of testing (some of the problems were less so when it was blocked). I've got some power back, but not the mpg. yet. :-)

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Old 06-06-2017, 05:19 PM   #60
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Join Date: Jan 2006
Location: NYC
Posts: 39,325
 

2003 L-Series 3.0L Sedan
Default Re: 2000 SL2 - MPG and power dropped. A lot.

With so many posts and members contributing ideas and suggestions, distractions are part of public forums. As long as you're able to progress, in baby steps sometimes, to address each suggestion and follow up with "nah, that wasn't it", "the pink balloon didn't solve the spark issue but is a great visual", "I'm lost!", whatever, keeps everyone informed on the same page, several pages later.

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