Ok I have a 94 B4C camaro with a 355 lt1, cc 304, long tube headers, borla cat back, 3 angle valve job, ported and polished heads and throttle body.

The problem:

The car runs extremly rich. The o2 sensors are running around .948 and boucing around to .860mv. The trim is at 128 constant and all sensors are running and responding correctly. Now the car had 2 burnt wires for the o2 sensor (brown and black) melted together. I replaced those and 3 grounds on the harness that were not connected. New opti, o2's, map, plugs, wires, coil. I have been told by 2 master techs that its the pcm but theres no gaurantee thats the problem so I want more opinions on the matter. The key is the o2's are reading rich but cant cut back fuel. Pressure is right on and no leaks in the regulator. I am baffled on if its something kooky or just the shorted wires fried the pcm so it cant learn again or even get out of open loop. Any ideas?

 

is the pcm tuned for the cc304 and the headers?

 

no but it ran fine at one point all the way for 23,000 miles on the build. And if so I have a 22 inch vacum on it so the comp shouldnt be running full rich from the cam. Its a mild cam anyway.

 

Could the MAF be sending incorrect frequency, and, PCM fueling rich??? Does the car run OK (better) in speed density mode compaired with closed loop (the MAF is not used in open loop, only MAP). I've had a bad O2, and the car (97) fueled rich.

 

Which trim is at 128 (long term or short term)? Is the car not getting out of open loop? Are you getting an SES light?

 

The car on a scanner says it is going in closed loop. The short and long are 128 and not moving at all. No ses light at all just lots of gas out the pipe. 0 miles a gallon in my garage..lol..

Also my o2's are both new and working great. They see the rich gas and read it boucing between 850 and 950mv...The pcm just isnt cutting back...I have tried 3 mafs I have here and I know 2 of them work for sure...

 

Long and short fuel trims not moving is usually a sign the PCM is either in open loop, or power enrich mode.

What are you MAP sensor readings at idle? (kPa or volts)?

 

I'm not absolutely positive on this, but I think the 02's do not read raw gas if that's what you are referring to. The PCM may think the car is lean via 02's and will want to dump more fuel into the cylinders which is where you are getting your rich readings from.... If that makes any sense whatsoever.
Again.. I may not know what I'm talking about. I know zippy when it comes to fuel maps and spark curves...
I'm wondering if you have any exhaust leaks around the primaries and/or collectors?

 

the map was around 3 volts until warmed up then it was around 1.8. The scanner even shows it in closed loop but like everyone says, the pcm isnt in closed loop if the trim is in a neutral position basically. I am just wondering if burnt wires and missing grounds would cause the pcm to trip out a bit or disable learn all together. I had three 20 year master techs look at this thing and they all say computer. lol I shouldnt doubt them as they know more than me, but you cant help but wonder if its possible. I know these pcm's are very strong and I here if they are toast you wouldnt be able to even start the car. I dont know what else it could be.

 

The factory service manual and the book "Corvette Fuel Injection" both disagree with you on that.


Brown is power and black is ground. Shorting them should have just blown the O2 fuse.

However, since you also had grounds disconnected, it's possible that the O2s and PCM circuits weren't properly grounded and then the short sent power into the PCM on it's ground. That would be a bad thing.


Overall, it does sound like you have a PCM problem. For it to say it is in closed loop but lock the BLM/INTs at 128 seems to indicate that the PCM is messed up. Might be fixable with a reflash, but given the possible power-to-ground problem I'd just replace the PCM.

 

ok, I have 4 wire o2's but it was only those two wires melted. well I did order a pcm from pcmforless cause I think the same thing. Thanks for all your info, just needed to ease my mind a bit on spending money on this car. I read similar post were they threw all parts and sensors then the pcm and still running crazy rich so I was hoping the pcm fixes my issue but theres no gaurantee..Thanks again.

 

I would agree on the PCM seeing a false lean condition and adding more fuel, but, his long and short term fuel corrections are stuck at 128 (which indicates a 'perfect' mix). Basically, the problem he is having, is the car is running extremely rich and the O2's seem to picking up on it (hence the higher voltage), but the PCM isn't correcting for it (leaving the INT's and BLM's constant at 128). There was someone not too long ago with a similar problem and no one could figure out what was wrong. I would assume your PCM is bad, but I don't know for sure. Maybe Injuneer can chime in with an idea. I have no idea why the INT's or BLM's aren't moving. Do be careful running it that rich; you'll wash the cylinder walls down and the oil will become very thin.

 

O yes sir I know of washing my walls out. I been changing the oil every other day while its been just idling in the garage. As for why my trim isnt changing is beyond me. We shall see if the pcm helps cause I dont know what else to test. I have probed every wire on this car from front to the rear(found a rear harness ground disconnected to so the kid could kill his tail lights, very stupid) thats why I went through the whole car.

 

Do you know anyone that would let you borrow their PCM?

 

No I wish, I tried to find someone but its not easy to get someone to yank there pcm for testing purposes. lol...Hopefully mine gets sent quick, I overnighted it.