This is for those who are having problems with the C4 corvette related to the PCM or ECM. An update on my costs so far in getting this PCM replaced. The original one was sent out to Module Experts for repair. It could not be repaired. They charge me 150 for their diagnosis. They wanted 1100 for a rebuilt one, I said no thank you! I went to several web sites looking for a rebuilt PCM 16181333 for the 1994 -1995 corvette. Corvette parts dealers have them but they are very expensive. The corvette parts dealers mostly have a rebuild service which is expensive as well, mine could not be rebuilt! Rock Auto is out of them as are several other major parts dealers. On ebay you can buy one rebuilt for 750-800 which are plug and play, more than I wanted to spend! Junk yards have them but the prices are all over 400 and up with little warranty if any, and who knows what you are getting? Then I found the part advertised from O'Rielly auto parts on-line. With the on-line discount the part was 97 dollars, with an 84 dollar core charge. I went for it. It says the the computer will need to be flashed. The part arrived quickly and looked good! I am sending it out to Oklahoma to have it benched flashed to my Vin. Hoping it will be the answer? So all total the rebuilt PCM has cost me 150 for the diagnosis of the old one , 100 for the rebuilt PCM and 100 for the flashing plus some shipping. around 375 so far.

I also learned that if you do not deal with a big company or web site you have no recourse when something goes wrong. If you are dealing with a big parts dealer, ebay or Amazon you can file a complaint and you get results.

This car has been a real learning experience so for whatever it is worth I wanted to pass this information on!

Thank you,
Rich Harris

 

I am back with new information but no repair as of yet. I received my rebuilt PCM flashed and ready to plug and play. I plug it in ready to experience a normal running corvette. It started out well but as soon as it went into closed loop it acted the same as it did with the original PCM. So here we are again! sooooo disappointing!

The car would not accelerate until I disconnected the MAP sensor. Once the MAP sensor was disconnected the car went into open loop and ran awesome. I am researching how to check the signal wire from the MAP sensor. The MAP sensor gets 5 volts, has a good ground and turns out a proper signal from the sensor.

After that I am lost! Everything else has been replaced or rebuilt. since the car runs well in open loop I have eliminated several major systems. Closed loop gets feedback from the sensors, MAP, MAF, TPS, O2, all have been replaced or tested. Fuel pressure is good even under load. I feel it is a fuel starvation situation. Is there another sensor that should be checked?
Thank you !

 

Yeah? Matthew already responded to this in a very professional way. I'm simply going to ask; Who's eating crow now??

 

If the car is still producing DTC's I'd pick the most likely one and start down the flow chart for that DTC. Then move onto the next.

I'd DEFINITELY have a scan tool on the thing and have it in data stream mode when it's going form open to closed loop. The only thing that really changes when going to closed loop is that the ECM starts reading to O2 sensor(s)...so I guess I'd be focusing on them....I can't remember all the codes the car previously generated.

 

Hi Richard, I've been following this thread. Sorry you're having so much trouble but I'm afraid it's inherent in these 25+/- year old cars with their antiquated EFI and electronics. Since I got mine this spring I've been spending most of my time with it learning about these 2 systems as I expect that eventually I'll have to deal with a problem.

A few who have posted have mentioned data logging and I think that could prove useful for you. There was discussion about interpreting the data you'd collect so I thought I'd take this opportunity to post this page I saved from my copy of the '92 FSM as a PDF. Have a look at it and see if it makes sense to you and is something you might consider doing. You have a copy of the FSM so I assume you'll find the same information (mostly the same maybe) on the same page in your manual. I've learned a lot from the data logs I've saved even though, in the end, I didn't have any problems.

Good luck with this going forward.

 

I think we should hold off on the crow eating until this car is fixed! It could still be the PCM. I may be dealing with rebuild and repair companies that are out to scam us! Since this post has over 4000 readers I will fix it just to see who really will have the crow dinner. Thank you for making this a fun experience! I enjoy the forum!

 

I have decided to buy a scan tool to read the real time data.I borrowed one way back in this process but it did not work well in real time I want a tool that can read both OBD1 and OBD2 data since I like to buy used corvettes 1990 on up. The 1994 is an OBD1 system but has an OBD11 16 pin port. I would appreciate some advise before I buy the scanner. Which one would be best for my situation? Actron 9680 or 9690 has these models that may meet my needs as well as INNOVA. I need a good one that will last but not break the bank although I am willing to spend what is needed. Thank you, I am over 4000 readers on this post and going strong!

 

For my old 94 the old Snap On “brick” as they called it worked well. I think it’s MT4500.

 

I bought a bluetooth dongle that connects to my ALDL connector and I downloaded a free phone app. ALDLDroid. I have the price of the bluetooth dongle tied up on it, that's all. I've posted a number of my logs here if you want to see what it captures.

 

lol not me, I never said the ECU was working, and it was indeed broken as confirmed by the vendor OP used. The cpu was fried. So the ECU was indeed bad, what is still yet to be determined is how or why the CPU got fried in the first place bc it seems like the car is going to fry this chip too. Seems like there is some bad wiring/grounding in the harness that is causing the ECU to fck up.

Not trying to pick any fights or anything like that. My sentiments are based solely on the fact that the OP was maligned for his working diagnosis and some members were pretty condescending in their advise. No one likes to be wrong, but it stings even more when wrong and also a d!ck about it too lol.

 

Actually, the OP sent it to a shyster outfit that told him the PCM was fried and couldn't be repaired, and they wanted to sell him a replacement for $1100. Doesn't seem like a trustworthy diagnosis to me! The OP then bought a replacement PCM from O'Reilly and got it reflashed by an outside vendor. And now that he's put this new PCM into the car...he still has the same problem. That's exactly what we said would happen, because the PCM isn't the problem and never has been. Something else is going on, but the diagnostics to suss that out haven't been done. Grounding issues won't "fck up" the ECU in a car, btw. But by all means, please keep telling us how it still has to be the PCM and that "the car is going to fry this chip too"...

Uh huh:
Definitely not picking a fight with that!

Quote:

Y'all treated this man like a noob and he was right, all along.

We aren't eating crow, the OP is a noob when it comes to diagnosing these issues (which is not a crime, btw), and the insistence that the PCM is the problem was most definitely not "right all along." Some folks here did get frustrated because after multiple suggestions to stop jumping to the PCM conclusion and to start with a real diagnostic process, the OP insisted that it would cost too much to do that and that the PCM must be the problem. There's nothing wrong with being a noob at something and asking for help and explanations. It can get a little aggravating when that advice and explanation is ignored, though. That said, he is heading in the correct direction now, and I suspect this will be a valuable learning opportunity for a lot of us. OTOH, you aren't helping by continuing to say that the PCM must be the problem.

 

 

still waiting on him to check all the connectors for good contact and continuity from the sensors to the ECM like I asked back in Aug

 

Indeed....and that is where frustration stems from (that Matthew was referring to). Give good advice and some people don't want to follow it. Then I become a dick...I guess? Didn't think that happened in this thread, but maybe...

 

Well maybe if he buys a scanner then reads his FSM a light will click and we can get this figured out

 

Just a side note to clear some things up. I bought this car last year because the past owner could not get it fixed. He spent several thousands (7000) on repairs. It was a low mileage car he owned for over 25 years. The car was at four dealerships and they could not repair it. They have repair manuals, scanners and much more training then I do. I have spent so far 3800 for the car which is in great original shape, paint, interior, wheels, tires etc. So far I have spent about 800 dollars. The C4's in this low mileage shape are going up in value so I am not under water just yet. I have the money but do not want to go over 6000 total and I love the challenge. I will buy a scanner tool which will not up my cost on this car, it is a tool I can keep and use in the future. The problem is electronic and it is the hardest to repair! Eventually we will fix it and the dealership that it was at last wants to know what was the problem!

 

I bought a Innova 3140g. It was priced right on ebay and it works on obd1 and obd2 systems. I will chart real time data on all the sensors when it arrives.

 

Be sure to capture some logs and post them here. I would save mine in Excel workbook format as most people can open those.

 

I received my Innova scanner and the company on EBay pulled a bait and switch on me. I ordered a 3140g scanner and they sent me a 6100 scanner. The one I received does not record live data. I have notified ebay and I am returning the scanner. I emailed Innova co. and received a reply that none of the Innova products will chart real time data. I am going in another direction. I ordered a ALDL cable and will be using the EEhack program and a lap top to diagnose the corvette live data. I have read that this program and the person who created it have done a great service to the LT1 94-95 owners. Hopefully I can get it to work!

 

Correction: None of the Innova scanners will chart real time data on my 94 corvette!