LittleNo

first of all, why i post this here: i think this is really EFI-related so the DFI-Forum should be the best position for this

i have here 2 Firebirds with the 3.1L V6, one is a 91, the other a 90

Both have exactly the same problem: when warm and in closed loop their idle becomes rough and finally after about 30 secs they stall. This only happens in closed loop, with disconnected O2-Sens they run fine all the time.

So i looked for the BLM and INT values on the Tech2, when the issue occurs the Long Term value goes down to about 100.

My first guess was a vacuum leak, so at one of the cars i replaced the intake gasket and checked (and temporarily disconnected) all vacuum hoses, but the problem is still there.

My next guess would be the Air injection Pump, but i don't know enough about how it should work so i don't know where to start. My guess is that wrong fresh air in the exhaust manipulates the O2-Sens-Value. What do you think about that theory?

RBob

iTrader: (1)

I would start by replacing the O2 sensors. When silicone poisoned they report rich. Which in turn drives down the BLM (long term fuel trim) until the engine cuts out.

When you pull the O2 sensors see if they have any white fluffy deposits on them. That is a sign of silicone.

AIR in the exhaust would do the opposite. Make the O2 report lean and drive the BLMs up.

RBob.

LittleNo

sorry, i didn't gave you a list what new parts i've put in, the O2-Sensors are new in both cars, when i pull them out right now they're black but seems to be normal

i also put new pickup-coil, EST-module, cap&rotor, new TPS, new CTS and new Injectors into one of them. That car also got new Spark Plugs

RBob

iTrader: (1)

What does the Tech2 show for O2 values? While in closed loop does the O2 swing rich/lean. Or does it just sit high. If it sits high I would then check the O2 signal from the sensor. It may be that the ECMs are bad, or that there are bad grounds, or something else.

Do the ECMs have stock GM calibrations in them. May be an issue with modified calibrations.

RBob.

LittleNo

both have stock cal's, in the car where i put a lot of new parts in is a reman ECM from Standard and a new MEMCAL from ACDelco

the O2 value jumps around like it does on all cars when in closed loop.

From what I can smell they're running good in closed loop and too rich when the O2's are disconnected, so I agree, it looks like the VE tables doesn't fit the Engine, but there's nothing changed from stock on both cars, they even have good compression and accelerating power

If it wouldn't be exactly the same symptom on two individual cars I would invest a couple of hours of work to edit the VE-tables to make them running smooth, but in this case here there must be anything going wrong and I want to find out what it is

RBob

iTrader: (1)

Certainly a strange issue. I am running out of ideas, but the last one would be to check the fuel pressure. And, check the FPR for fuel leakage into the vacuum line. It may be that there is a pin-hole in the FPR diaphram.

Not sure if the cars have auto transmissions. But if they do an idle learn is required whenever the battery is disconnected or the IAC is changed. The Tech2 has this built into it for a fast learn.

Can also do a slow idle learn without the Tech2. I found out about the idle learn procedure the hard way after a battery disconnect. Stalling, rev'ing up, surging, all kinds of issues at low throttle openings and at idle.

RBob.

LittleNo

good to see I'm not the only one running out of ideas, this is really something strange

Actually I did most of my tests with the Fuel Pressure Gauge connected, so I can say for sure the Fuel Pressure is in a good range (40-45 psi) all the time.

The Vacuum-Line of the Fuel Pressure Regulator I had fully disconnected while my search for vacuum-leaks.

One of them has a slight play in it's thottle blade shaft and had a high idle due to a steady TPS angle reading of some %, I turned the TPS a bit to make sure it reads 0% with closed throttle, that fixed the high idle issue and after that I did the idle relearn. But I don't think this problem here is related to the idle learn because in open loop the idle is fine (regardless of cold or hot engine)

Today I guessed for a clogged Cat and measured the pressure inside the exhaust, but it won't exceed 1 psi (not sure what this exhaust system should have, but 1-3 psi I think it should have, so maybe the Cat is not clogged but no longer present but that shouldn't be related to my issue)

RBob

iTrader: (1)

The less then 1 psi on exhaust backpressure is OK (pre-cat).

Without being there it becomes difficult to troubleshoot. However, it appears that the problem is only when the car(s) is in closed loop. That is where I would start.

At the same time how does it run and drive with the O2 disconnected. I guess what I am trying to say, is the problem being caused by being in closed loop. If so, it is fully on the signal from the O2 sensor.

The ECM will adjust the INT & BLM to get the O2 voltage within the correct range. Nothing more to it.

Maybe the new O2 sensors are bad? Won't be the first time anyone here has seen new parts that don't work.

If you have a 4 or 5 gas analyzer that can also tell a lot about the AFR. Can check what it reports against what the O2 sensor reports.

RBob.

LittleNo

yep, the problem is only there when the O2 is connected, without the O2 it stays in open loop and runs fine all the time

ok, i will try to hook it up to our State Emission Tester to see what's the real O2-value when the problem is there

JJx91camaro

i would check the egr, seems to cause alot of problems like this

LittleNo

well, yes, thats the only thing i haven't eliminated yet, that can be a good idea, i'll try

LittleNo

damn, that EGR really was the culprit, i put a piece of metal between the EGR and the exhaust manifold and everything is fine since that

the strange thing is, on my search for a solution i thought about the EGR every now and then and looked at the Tech2 if it is activated when the problem happened but it never was ... so the only explanation is that the EGR becomes leaking when getting warm

one2burn

I have a 91 rs 3.1 v6 that has the same prob. no codes but when gets hot stalls and won't restart but I took out the prom chip put it in the freezer because a guy wrote to me that his chip was bad and same prob. he replaced the chip and alls fine so I think I might have the same prob. as him but thanks for posting because EGR is controlled and I am going to dis. con. the o2 sensor just to check it out can't seem to find a stock complete memcal with chip for it right now anyway. Thanks George.

LittleNo

well, I already got headaches only from the presense of this bad word E-G-R ...but: was there question contained in your post? if yes, please say it more clear and I will do my best to answer it ;-)