Jerky Saturn problem narrowed down to EGR valve. What next?

[1996SL11.9L]

How can the exhaust deliberately being put in the air stream lean out the fuel mixture?

It is already a dead, spent, inert gasses. It takes place of some of the combustion air and lowers the volume of intake air with O2 in it. The fuel injection doesn't measure the amount of combustible gasses in the air stream. So it is adding fuel according to the fuel map that is skued for current operating conditions. There is a lower volume of combustable air in the cylinder then is expected and there is more fuel then avaliable O2 to burn it because some of the intake air got displaced by exhaust from the EGR. And his LTFT was -14 or whatever. It was rich and almost coding for an excessive rich condition.


Most engines under acceleration cut out / kill the EGR for performance propose. The fact that acceleration adds more volume to the exhaust stream creates more back pressure because the CAT can only flow X amount of air. That lifts the valve seat of the EGR and allows exhaust to spill over into the combustion air.

Blocking it off makes it happy. Replacing the EGR valve didn't fix it but blocking it off always does..............

[fdryer]

Here's a partial reprint from the FSM;

EGR System Operation
The exhaust gas recirculation (EGR) system is used to decrease the emission levels of oxides of nitrogen (NOX). NOX is a group of chemical compounds containing nitrogen and varying amounts of oxygen, which in large quantities, can have harmful environmental effects.

NOX forms during the combustion process in amounts that are dependent on the concentration of oxygen in the combustion chamber and the duration that the combustion process exceeds 822°C (1512°F). Decreased NOX levels are accomplished by reducing the peak combustion temperature through the dilution of the incoming air/fuel mixture with exhaust gas. Exhaust gas, largely non-reactive carbon dioxide and water vapor, reduces combustion temperatures because of lower oxygen content.

Correct amount of EGR depends upon the geometry of the combustion chamber and the operating condition of the engine. Too little EGR can yield:

High NOX
Spark detonation
Engine overheating
While too much EGR can yield:

Reduced engine power
Engine stalling at idle
Rough idle

My interpretation of diluting the incoming air/fuel mixture with egr is to lean out this mix overall. I've sent a pm to the OP to find out if the catcon will be replaced or left as is as this is part of your basis of the egr valve error that would alter my understanding of the P0401 code. I somehow ignored the catcon clog(?) since the OP did pass inspection. Further researching about the P0401 code made me read more about the map sensor data posted and possible discrepancy for or against your point of view. I see a lower than normal map number at idle and do not know whether its caused by the clogged cat or the sensor is faulty. I used info from here; http://www.aa1car.com/library/map_sensors.htm.

[quantumech]

BennySL2: Sorry, I went out for a backpacking trip to blow off some irritation and steam before the job hunt begins (again...sigh), didn't see your message, but glad that it looks like you figured out your problem.

1996SL11.9L and fdryer: perhaps we can take a quick look at the chemistry involved. The main point of EGR is to reduce NOx emissions, which are very environmentally unfriendly (contribution to greenhouse gas, acid rain, etc). What happens when it's recombusted is the N and O's dissociate from each other, forming elemental nitrogen and oxygen, which then can go off and react with hydrocarbons that are present. Or the monotomic oxygen reacts with the nearest hydrocarbon, it would really depend on what it runs into first. The formation of N2 is a very energetic and exothermic process (why compounds containing nitrogen tends to be used in explosives), which can drive the oxygen and hydrocarbon reaction for that split second after the spark.

In the end, there is probably a small effect on lean/rich, but if the system is working correctly (notice the "if"), it shouldn't have a dramatic effect in either direction. I would imagine that during one cycle it could be lean, the next rich with the EGR in operation, depending on what the oxygen sensor is reading.

But that's just a guess (what the car is thinking, that is), I'm just a chemist, not a mechanic afterall. I'm just thinking about the chemistry of the situation to try and help you guys out.

[BennySL2]

Here's an update. This info probably won't help the immediate discussion, but will be useful if anyone has a similar situation.

I called around, and found that what I was quoted at Midas ($913 for a direct fit catcon and exhaust pipe, O2 sensor, plus 10% tax, plus $40 shipping of a particular part) was on the high end. I ultimately went to a regional emission specialist shop. They tested the rear oxygen sensor and said it was fine. Parts, labor and tax for the flex exhaust pipe and a universal Catcon was $390.

How does the car run? Like a dream. The EGR-related jerking is completely gone (while driving and idling). And the car has incredible pick-up. It's like it's a different car.

A note about the P0401 code: There's a chance the P0401 was caused solely by blocking the EGR valve. While diagnosing the problem, I never reset the codes because I needed to try to pass the OBD-based emission inspection in short time, and it can be problematic to quickly complete the drive cycle. So, when I blocked the EGR valve I would have a P0401 code and a SES light. When I unblocked, the SES light would turn off, but I would still have a P0401 code. When the car passed inspection (prior to fixing the catcon, with unblocked EGR valve, NO SES), my code reader said it has a P0401 code, but the state's computers clearly stated that there were NO codes. So, I don't know what's happening there.

I wanted to post some new freeze frame data, but the car still has the same data as before (and the P0401 code). I reset the codes, and I'll know more after our weekend trip.

[1996SL11.9L]

bet your LTFT is back to normal instead of -14.

with 160,000 on mine I should do it as well but cant justify it yet.
If I play hard sometimes I will get the 1406 pintle home code. it only happens when I wood it and run it through the gears hard.

The 1401 is expecting to see a rich condition with egr open if it doesn't see it......SES.

[quantumech]

I believe the state only is concerned with codes that are active, not codes that are stored in the history. They may also be interested in pending codes, I'm not sure. I obviously don't know your reader, but is it possible that it is showing currently active and past codes at the same time?

Where did you get the new exhaust (for future reference)?

[fdryer]

Originally Posted by 1996SL11.9L

bet your LTFT is back to normal instead of -14.

with 160,000 on mine I should do it as well but cant justify it yet.
If I play hard sometimes I will get the 1406 pintle home code. it only happens when I wood it and run it through the gears hard.

The 1401 is expecting to see a rich condition with egr open if it doesn't see it......SES.

I'm sure you mean P0401 (easy to transpose numbers) and I have what may be considered another reason for the egr valve code being separate from the clogged catcon; many here with definite clogged cats have never posted any egr error codes. All have posted the same symptoms; inability to accelerate, poor engine running, fuel starvation, ignition problems, etc.. None posting anything related to the egr valve. Once its determined that a stuffed catcon exists by removing the front O2 sensor, power returns from the temporary alternate exhaust outlet bypassing the normal route. The catcon is replaced.

I too am interested in the new freeze frame data.

[1996SL11.9L]

yea, I meant the 0401.

FYI my innova scanner has an amber light for pending codes and red for actual codes.

My scangaugeII thinks both the pending and actual codes are the same. It tells me there is a code, but with no SES its a pending one, or recently corrected and not enough start cycles happened with no problems related to the trouble code to clear it from memory. (I think the Saturns also do this)

[fdryer]

The FSM describes the pending codes staying in history (with the SES light OFF) so a programmed number of engine cycles without the same error coming back will reset the history. Some error codes requires up to 40 cycles while others much less like the loose gas cap. With the SES light OFF all cars are supposed to pass emission inspection. Some shops may confuse pending codes as not allowable but the SES indicator being OFF means the car has passed all federal and state requirements to issue a new tag. Other than the bulb being burned out, no error codes (including pending ones) just means PASS.

I was surprised when my first inspection with my L300 didn't require the anal probe (tailpipe sniffer used for pre OBD I[?]) vehicles and passed immediately before the inspector plugged my car into the NYS DMV for the paperwork. That first inspection took less than 15 minutes. Now that my car is older the same inspection station takes 15 minutes to do the walk around for the mechanical inspections.

[BennySL2]

Originally Posted by quantumech

I believe the state only is concerned with codes that are active, not codes that are stored in the history. They may also be interested in pending codes, I'm not sure. I obviously don't know your reader, but is it possible that it is showing currently active and past codes at the same time?

Where did you get the new exhaust (for future reference)?

Yeah, I think it is possible that my coder (Pro-Series CAN OBDII Code Reader, http://www.diydiagnostics.com/ ) doesn't distinguish between past and current codes. It does distinguish between pending and current codes though.

I got the exhaust work done at Walt's Emissions (the shop on Aurora). I'm happy with their service.

[BennySL2]

Here's new freeze data and live data from idle. I'd be glad to get any other data, if wanted. The car is still running great. No EGR valve errors, no hesitate, great acceleration. (My smog pump/"secondary air injection system" pump blew last week with a P0410 code, but I'm going to start a new thread about it.)

In retrospect, the only test that I should had done but didn't was to remove the oxygen sensor and then driven the car. This would had told me earlier that the catalytic converter was clogged. It's an easy test, but I was myopically focused on the EGR valve...

One more note about the EGR valve. The pintle on my original valve would stick open when pushed in. Cleaning it didn't help. The used one I replaced it with works fine. I'm thinking that the EGR valve needed replacing anyway.

The data: "Old catcon/jerking car" → "New catcon/smooth car"

FREEZE DATA
fuel sys 1: "OLCL using HO2S" → SAME
fuel sys 2: N/A → SAME
load %:11.7 → 18.8
coolant F: 171 → 160
STFT RM1 (%):18.7 → 0
LTFT RM1 (%): -14 → 0
MAP (inchHG): 5.32 → 7.97
RPM: 2533 → 937
Speed(mph): 60 → 0
IGN ADV: - → SAME
air intake temp(IAT) F: not given → SAME
throttle pos(ABSLT TPS %): 0 → 0
OS211: not given → SAME
OS2S12: not given → SAME
Second Air: ERROR → SAME

LIVE DATA(idling after driving)
fuel sys 1: "OLCL using HO2S" → SAME
fuel sys 2: N/A → SAME
load %: not given → SAME
cooland F: 205 → 207
STFT RM1 (%): varies 0-3 → varies ~0-2
LTFT RM1 (%): -14.8 → -3.9
MAP (inchHG): 9.45 → 7.97
RPM: 850 → 850
Speed (mph): 0 → 0
Spark advance/IGN ADV: varies 10 to 20 → 2 to 20
air intake temp(IAT) F: 98 → 100
throttle position(ABSLT TPS %): 0.3 (pushing the gas all the way down gets 90%)→ SAME
OS211 :varies .1-.8 (0-3%) → varies
OS2S12: varies .6-.8 (n/a%) → varies
Second Air: ERROR → SAME

[mrbios]

Originally Posted by fdryer

Too many people become overly concerned about gunk/grease/oil/carbon deposits inside the intake manifold.....

I totally agree. I'm the original owner of my 1997 sw2. I finished replacing the head gasket last week. The intake had plenty of carbon crud. I didn't waste time cleaning it because it wasn't causing a problem. My warn out head gasket was dumping exhaust into the coolant bottle and even turned it black from exhaust. Replaced the HG not more bubbling over of the coolant.

I just found a 7/16" vacuum hose that was off just under the intake manifold and put it back on. I think it is for the Charcoal canister purge. No codes. Warm idle fell to 900 from 1100 or so. Yesterday, I removed and cleaned the throttle body and the IAC and installed a new gasket. I should have left it alone because it has never been cleaned or removed and worked perfect. After I started the car the motor reved up to 1800 rpms so now I know it is messed up and will replace it with another from the junkyard.

I just posting this to suggest leaving the IAC alone and address the real problems not just remove and clean parts in the hope that will be a magic cure.

Pe@ce Out.

[satmark]

I'm really glad this thread popped up. I have an EGR insufficient flow code that comes and goes. I've tried all the usual cleaning fixes/replacements but never thought it might be a clogged cat. Definitely something to check - thanks!

[1996SL11.9L]

Originally Posted by satmark

I'm really glad this thread popped up. I have an EGR insufficient flow code that comes and goes. I've tried all the usual cleaning fixes/replacements but never thought it might be a clogged cat. Definitely something to check - thanks!

Before taking the CAT route you first need to remove and clean the back side of the pintle on the egr valve.........

then while its off try and run a wire rope or what not into the hole that comes from #4 cylinders exhaust port. Of coarse get it in as far as you can to brake up the carbon deposits blocking the passage. then plug in your EGR valve and let it hang by the harness and start engine. It will rev pretty high let it for 4 sec and shut engine off........do this until no more black carbon comes shooting out of the hole where the EGR valve mounts.

Edit: The better way to clean that passage it to remove the exhaust manifold where you will have access to the passage inside #4 exhaust port........but you may get enough with the wire method from the other end.