bley49

Updated
Maf
Fuel pump
CTS
Fuel filter
O2 sensor
EGR valve gasket
Minimum idle and TPS adjustment
ECM is replaced with factory PROM
Throttle body gasket is done and tb is clean
New IAC
Spark Plugs AC delcos and Wires
Intake manifold gaskets
EGR is brand new
Air Filter cleaned

1985 L98 stock minus exhaust
Probably a couple things I'm missing

Everytime I replace something it seems better but goes back to its old ways in a day

VikingTrad3r

The next thing i would check for is a vacum leak ahead of the o2 sensor but after the manifold, which artificially makes it look to the o2 sensor that its running lean (cause more air has been added after the combustion), and secondly i would do a leak down test on your fuel rail, it is possible that your injectors are leaking like seives dumping fuel into the system.

but I am not an expert, just learning, and this is what I would do if it were me based on what I have read on here by the experts.

Also I'd remove the chip.

Hope this might help you.

bley49

thanks for the imput i forgot to add all the vaccuum lines are new without any leaks

VikingTrad3r

its good those are new. my understanding is that a vacum leak ahead of the combustion creates high idle (u dont have) and that vacum leak in exhaust(?) after combustion (but drawn into the system as it flows out the exhaust system) may cause an o2 sensor to read high o2 (cause of the fresh air mixing with actual exhaust gas) and therefore instruct more fuel to be input, causing a rich condition which is what your describing.

have u verified your plugs are being fouled by pulling a couple from the easy side? (driver).

and i would do the leak down test for the injectors.

bley49

Plugs are new and all good also forgot to add those to the list

Cliff Harris

The ECM controls the AFR based on the CTS (Coolant Temperature Sensor) mounted on the front of the intake manifold under the throttle body. If the sensor/connector pins/wiring is bad the ECM will think the coolant temperature is -40°F and will richen up the mixture.

Check for error codes in the ECM:

http://forums.corvetteforum.com/1574918379-post18.html
http://corvettephotographs.com/c4vettes/codes.htm

What they mean:

http://forums.corvetteforum.com/1576116036-post35.html

bley49

sensor and connector pins are new and all good now no codes on the ECM

pcolt94

Fuel injectors seems to fit the symptoms of the problem. On these years cars injectors are always getting replaced. I would get them checked or replaced.

viii

many years ago I had similar issues. stumble, unpredictable cutting out, turning really rich, (soot on the bumper rich), car was possessed. turns out it was the ECM that was bad.

l98tpi

How do you know it is running rich and not starving for fuel?

First thing I would do is put the stock chip back in. If it still runs rough, I would check fuel pressure and then injectors.

bley49

funny thing Viii my mechanic said it was possessed, I already got a new ECM with a PROM on its way

HlhnEast

I think you are on the right track here. One thing you mentioned is the car runs fine for about 10 minutes. If this coincides with a battery disconnect, the reset ECM goes back to square one and then starts getting input from all sensors to make adjustments to engine function. If the aftermarket chip is causing issues I would think it might take a bit for the car to start showing up. I dunno but its a thought.

You did miss the boat a little bit by not upgrading to a later ECM tho. Theres nothing wrong with the 85 computer but the 86 and later ones are smarter and are more tuneable. If mine kicks the bucket I am planning on doing this. At the rate my car is puking parts I figure it wont be long.

Since no one has suggested it I would check your fuel pump relay and the wiring there. The insulation shrinks away from the connectors and sometimes these wires get frayed and start losing their full current potential or strands cross over to other wires. Not necessarily saying this is the smoking gun but something to look at as a preventative item.

Good luck and keep posting when you have solved the issue. I am having fueling issues with mine so I will be very curious as to your results.

bley49

I appreciate the help gentleman yeah, I wouldn't have jumped the gun on the ECM and PROM so fast if it wasn't so hard to find a factory PROM

Capt Mike

Let us all now your results with the new ECM 7 PROM

Also, try removing the top plate on you Throttle Body. Make sure the gasket is good and the airways are clear & clean,,

Good Luck

bley49

airways are clean gasket is new thanks for all the tips though I'll be glad to update when the new ECM is in because I heard some others are having a similar problem

bley49

Newish ECM swapped in with a FACTORY PROM what a difference! For now... did the swap at midnight after work tonight drove it about 20 miles with multiple starts seems like a new car one start did throw up a a check engine light will investigate further so far so good. I appreciate all the tips and help from this threads and it predecessors you guys are the best! Will update after driving it to class tomorrow.

HlhnEast

Sounds like you may have it licked. Wait a couple days and report back. For some reason, my car fools me, running great for two days, then reverting back to its bad habits.

Capt Mike

Great News,

Alex does my PCM Tuning, does a fantastic Job !
\
http://www.pcmperformance.com/

Turbovette LT1

Pull a plug and post a pic, a lean condition can fool you. Burn you eye and stink up the garage badly

86C4Z51

I put a chip in my ECM years ago and thought I'd lost the original chip. Never throw that stuff away. I found it in a box of stuff after we moved. Whew! Mine's an early 86 with iron heads and auto, so it's a pretty specific chip. I guess they all are, but try to find the factory chip ha ha.