ksphar

I'm fighting a problem with my car running rich at idle and popping through the exhaust. Car is fairly stock, but has 1.6 rockers on it. To watch it on Datamaster, the long term fuel trims always show about 118 on the left and 108 on the right. I have swapped injectors between sides on the engine with no difference. Plug wires measure around 5k, which should be good. Map sensor seems to be working ok. I checked EGR with a vacuum pump, and it seems to move ok. Also checked FPR to make sure gas wasn't leaking back through it into the intake. It has done this since I owned the car for about 6 months, and the car had sat for a long time before I bought it. Any ideas? Thanks in advance?

ittlfly

You might check out this thread.
http://forums.corvetteforum.com/show...25&forum_id=48

Alvin

If you send me a datalog I can give you some hints.. chips@pcmforless.com

ksphar

I have read that post and still can't determine my problem. Also forgot to say that I replaced the O2 sensors about a week ago, and it didn't change the problem. It runs great in open loop, and then idles rough and goes rich in closed loop.

Morley

Open loop is operation is affected by the TPS & MAP. The O2, EGR & ESC don't really come into play until the CTS reaches a specified temp. If the CTS is sending bad info to the ECM once it reaches closed loop temps the ECM's fueling will be incorrect.
Since you have datamaster up and working, take a look at the coolant temp readings in it as compared to your gauge. If there is a big difference you have found the culprit.

ksphar

This may be a stupid question, but doesn't datamaster get the same signal from the sensor that the dash does? Wouldn't they both read the same even if there was a problem?

I also noticed that on Datamaster that there is a 0 or 1 switch that says ESC ( i assume Electronic Spark Control) enabled. I have seen that switch between 1 and 0 when driving. Where should it be and what exactly does it mean?

brookman

Have you pulled the valve covers and checked to see that the intake valve on the side that is popping is actually opening?

ksphar

Yes, I have checked the valves. If it was a valve problem it would show up during open loop as well, wouldn't it?

Lichen

This would be my first guess. The temp reading on you gauge has nothing to do with the other engine temp gauge. It's a cheap fix.

ksphar

I got to thinking that my car is a 92 which is batch fire. According to the Datamaster manual, my readings for fuel trim aren't split left and right, only for the later SFI cars. I also read somewhere on here that's why they GM switched from Batch-fire to Sequential. The car runs great at upper RPM's. Am I just worried about nothing with a little popping in the exhaust? Is this normal for a batch fire car?

Morley

No, that is not normal operation for a batch fire system.
Your other question..The ECM doesn't get its temp reading from the same place as the dash gauge. The coolant temp sensor is located in, on / near the intake manifold. The temp sender for the gauge is located in the driver side cylinder head.

ksphar

I replaced the coolant sensor today and it does the same thing. In regards to the batch fire, I had read somewhere on here that 92's had a recall for idle quality and that is why they went to SFI. I wouldn't call the popping in my exhaust loud, more like it has a slight misfire at idle.

ittlfly

With the 108 BLM on the right side, the ECM is not in control of the fuel delivery. Your right side O2 is living well above 450mv....left side, less so. The upshot is that the ECM cannot substract enough fuel on the right side...and that is where (IMHO) that the popping is ocurring. The unburnt fuel is igniting in the CAT(s). My 92 has been doing that exact same thing for a couple of years ....however my BLM's are not as far out of range as yours. I really think the problem is in the valve train somewhere as I have replaced everything except the IAC and TPS over the last year. It may be a weak/ broken valve spring etc. Since I will be upgrading to a C-5 (or maybe a new C6 )....I'm just living with it. Like you said, it runs just fine in the higher RPM's.