I recently purchased a C5 model vette. The car has a vortec supercharger on it and it also has long tube headers with no catalytic converters. I drove the car for about 250 miles and it started acting up. It stuttered at 70 MPH once and at idle stalled. I was able to get it re-started and driven to my house but it has gotten worse. Now it will not run long at all. I can get it started but it will just idle for a minute or two, all the time stumbling, then it will stall. It seems that if I let it sit for a couple of hours it will almost go away, but after a couple minutes of running it will stall again.

Here is what I have done so far to no avail:

1. I had it towed to the dealership and they let it sit for 3 days before working on it. They then performed a factory recall on the column lock and checked it out for the rough idle issue and came up with nothing. I then went to pick it up and it did the same ol thing over again.

2. I drained both fuel tanks thinking I had bad gas. I replaced the drivers side fuel pump, and removed the passenger side unit just to be sure I had completely drained both tanks. I then added fresh 93 octane, and the problem was the same.

3. I saw a lot of posts from Bill C and others on here about bad grounds, water leaks, etc and thought I'd tackle some of them to see if they solved the problem. I cleaned the four (4) major grounds in the engine compartment completely.

4. I removed the passenger side inner fender to gain access to the AC drain. I cleaned the drain tube completely. It had some debris in it, but nothing major. I also cleaned the drivers side three tubes since I was at it.

5. I checked the firewall drain tube by squeezing it, and it is soft, no crunching or hardness as if it were clogged so I left it alone.

6. I removed the panel in the floor on the passenger side and inspected the area for burned/shorted wires, water, etc. But, no signs of anything suspicious.

7. I cleaned the key and the key slot with alcohol well.

8. I inspected the wiring harnesses that go to both doors as Bill C noted on his excellent posting but there were no signs of any problems, they actually looked in really good condition.

9. While I had the passenger side inner fender panel out I found the largest problem of suspicion. One of the previous owners had broken the bracket that holds the PCM to the frame and had actually used large zip ties to secure the unit back in place. I had driven the car in heavy ran both times that I have driven it and noticed that the bottom of that panel goes up under the car somewhat and has a drain in it for water that gets into that area. However, the "jury rigging" of the PCM by the previous owner had allowed the PCM to slide down to rest on that panel bottom and water was collecting there. When I removed the panel, I found that all the wiring to the PCM which is on the bottom of the unit was soaked. I am suspicious most of this area as the cause of my problems, but am not sure how to proceed further without just replacing the PCM unit. I assume that if I do that, I'll have to send it out to get a temporary flash of the unit until I can get it to a Dyno for proper tuning.

Questions I have:
- Can I do any inspection of the PCM without loosing the tune on the car such as disassemble it?
- If I buy a new PCM, can most tuner shops put a temporary tune on it just so that I can get it running to bring it to their shop, or can I run it on the stock tune just to get it onto a trailer ?
- Can I completely remove the battery without problems or loss of the current programming ?
- I have read of a procedure for resetting the computer idle and WOT settings by pulling the #16 and #23 fuses, will this screw up the current program of the fuel system.
- Has anyone else had this problem ?

The local dealer that looked at it before is supposed to be coming to get the car today to take it back to their shop. They will again run a diagnostic on it. With the problem now occurring regularly, it should do it for them.

Any help from you guys would be great.

Here are the codes that are currently showing:
58-SDM B0026H
60-IPC B05126 and U1064H
80-Radio U1064H
99-HVAC B0338H & B0361 H C
AO-LDCM 1064H
AO-RDCM 1064H
BO-RFA U1096H, U1064H, & U1016H

The check engine light has never come on except when inserting the key to start the car as normal when in the ACC position.

As I said, this is my first corvette, I have always wanted one, but this is not the way I wanted to start my relationship with them. I am very mechanically inclined and can tackle just about any part of this car, I just don't know where else to look for answers. Thanks in advance for any help you guys can give me.

Thanks,

 

no thoughts guys ? This is driving my nuts.

 

As far as the codes ....
I'd be much more suspicious of the water around the PCM. I'd remove the PCM from the car and carefully dry and clean all the wiring connectors. I'd do the same to the connectors on the wiring loom. ANY WIRING GLITCHES in the cooneections to the PCM can easily cause the problems you're describing.

If after cleaning/drying everything and putting it all back together and the engine still runs badly, you may have to let the dealer do the work. Replacing a PCM requires the use of a Tech2 scanner to not only program the PCM with the VIN, but the BCM has to be "re-synched" to the new PCM and a Tech2 is required to do that.

Simply removing and cleaning the PCM should not cause you to lose your "tune", but a new PCM will (duhhh ... ) end up with a stock tune after the dealer has loaded it with the Tech2.

HTH

 

Thanks for the reply. I was beginning to think I would be going this alone. I'll delete the ones you recommend below and will get into cleaning the PCM this evening. I plan to use simple compressed air to blow dry the plugs on the PCM and then electrical cleaner. I'll get it back together by morning and touch base back then so anyone else that has the problem can follow the steps I took. Worse case scenario, if this doesn't work I may have to go the new PCM route then take it to be re-tuned.

Thanks again.

 

half of the stuff you checked has nothing to do with how the engine runs. I would check for a vacuum leak first and foremost.

 

Mike, any ideas on where to start for the vacuum leak ? Are there certain areas or connections that are prone to problems that are known to corvette owners ? I'll check all the connections I can find in the morning.

Thanks again guys for all the help, I need it here.

 

ttt

Good luck, hope you find a fix soon.

 

I have look at your post and i have a few questions. What is the size of your injectors? What is you present fuel pressure? Do you have a meth kit? do you havd a booster pump? Have you checked for vacuum leak and how did you accomplish this feet?

 

JR,
- the car has 42# injectors that came with the kit.
- As for fuel pressure, I am not sure because there was never a fuel pressure gauge installed. I will be changing this ASAP.
- I do not have a meth kit on the car
- I do not have a booster pump that I know of. Is this a secondary fuel pump installed somewhere ?
- I have not checked for vacuum leaks with any gauge type device, only a visual of the hoses I could find. This was mentioned to me in a previous thread, are there key ones to look for that are troublesome?

Thanks in advance for your time. *****:

 

First, I would pull the plug on the PCM and make sure there isn't any water or corrosion. But these should be water tight.
Second, I would check all the vacuum lines, and the hoses for the charge tubes. And also, may try getting some MAF cleaner and clean the MAF. IF someone just cleaned the air filter, then may have put too much oil on it.
You really need to get a Fuel pressure gauge if you are running boost. And I would suggest a wide band also. It would also be a worthy investment to buy yourself a tuner software. One, you can upload and save your tune file. Second, you can do some monitoring with it yourself.
Good luck, and let us know what you find out.

 

I have an Innovate Motorsports, LM1 unt and have used it on my big block chevy, I just haven't gotten the chance to put the bungs into the exhaust on this car yet. I'll be going over the vacuum lines and PCM plug as you mentioned and will report back with anything I find. If it's as ugly as the "jury rigging" of the PCM that I previously found, I'll attach pictures for your amusement.

When you say "charge tubes", do you mean the hoses on the pressure side of the supercharger to the MAF unit.

Thanks,

 

Yes, all of the silicon hose connections between the blower (Or Turbo) and the intake manifold. Also, check to make sure your narrow band 02 wires hasn't got up against the exhaust and melted.

 

There are two (2) oxygen sendors in the exhaust, and the wiring to both of them seems to be melted sligtly due to poor routing and close proximity to the header tubes. I can't see any clearly bare wires but these are definately suspicious. I think I'll replace them.

Would a failure of the signal to the O2 sensor cause the car stumble and not run ?

 

Yes the O2 sensor I forgot about them. If they are melted thats a problem. Signal fail from the sensor will cause a problem and cause the car to run badly . also it won't idle good at all. Are they melted through? if so, please replace. Please keep us informed.

 

they're not melted through, but that cheap corrugated PCV wire looms that they us on the cabling is melted completely and the insulation from the wiring is slightly melted. I'm going to remove them and go get new ones in the morning.

Thanks again guys for all the support, it is great to know there is somewhere like this to go for answers that even the best of us can't seem to figure out some times.

 

Well, no update on the solution to the problem here. The GM dealer is lost at this point.

I checked all the vacuum lines, all the hoses to and from the supercharger with no signs of leaks. I managed to get the car to run for about 15 minutes one day, how I don't know, and checked for leaks on all the hoses with no signs of anything. The car does have a boost/vacuum gauge in the car and it has been registering 15-20 lbs vacuum at idle when I managed to get the car to start.

I have disconnected, cleaned with electrical cleaner, and reconnected both wire buss plugs that connect to the PCM, Mass Air Flow sensor, and the Throttle position sensor.

None of these have worked.

As of now, I am scheduled to take the car to CAM on Friday to see if they can figure it out.

Anyone have any experience with them in the past good or bad ?

 

If Jeff can't figure it out...........no one can

 

Thanks for the input on Jeff's team. I went by the shop yesterday just to check it out since I happened to be in the area. He definately seemed confident that he will be able to get it figured out, and I sure hope he can. He was kind enough to spend 30 min with me even though he seemed up to his eyeballs in work.

I'll keep you guys updated.

 

If you have taken it to the DEALER for a recall,,,,,did the dealer reflash the PCM?????? If the PCM was reflached, your back to a stock tune and that is NOT good for the MOD level that your at!

Check with the dealer and see if the specific recall that they did involved a PCM /BCM reflash. I bet you that it did! Hope you live close to the shop that did the tune.

Bill C

 

Bill,
I checked with the dealer and they did not reflash the PCM to do the Column Lock recall. I can't help but wonder if there is anything in the emissions control system or vacuum system that is stuck like a diaphragm somewhere that wouldn't throw a code but could shut the car down. What about a MAF unit failure, do these things crap out and cause the car to shut down without tossing a PCM code ? Is there some kind of vent or vacuum line in the fuel system that would cause the car do die ?

Here's a funny one. I was curious if I was even getting spark at the plugs. So, just like I do on my big block, I pulled one of the spark plugs, connected the plug wire to it and held it against a header bolt to ground it and had my wife turn the car over to check for spark. The plug sparked fine, and then the car started, ran crappy, but started !! It only ran for a couple seconds until I waived for her to shut it off. I put the plug back in and right back to the same old problem. What gives with that ?


Thanks for the thoughts.