Help! Corvette gone crazy

[airman]

I have a 1990 and it is driving me crazy everthin has worked great for years but now after running for a bout five minutes the temp control starts flassing and I can not cotrol the heat or air I turn on the air and it will turn on the heat after a little bit or it may turn on the fan and if I turn it off it will turn it self back on. At the same time the diggital dash will start blinking jiberish that you can't read it is so bad that I don't want to even drive it. I think it may be a computer but wich one and the one onder the dash well I can see it but can't get to it.Any Ideals ?ad

 

[Schrade]

It's not the computer. It almost NEVER is the computer.

You have grounds which are poorly connected / corroded, including some in the LCD dash panel.

5 minutes you say? Is it happening at about the same temperature? Answering this is a definite clue. When it goes to closed loop, at a SPECIFIC temperature, and all sensor circuits get energized, a failed ground in one of those circuits would be easier to find - especially if one ground serves several circuits.

Do you have a multimeter?

Do you have any check engine lights? If so, do you know how to pull codes with a paper clip?

If you break down your posts a bit (grammar / punctuation), it will help your thinking skills that you will need to solve this electrical problem - seriously...

 

[airman]

I have a Snapon scan tool there are no codes. I have checked all the grounds that i could find, I've even added a few direct to the computers with no change. I will hook up my scanner and watch to see if it starts at closed loop. Temp does not seem to mater. I have been working with this sense early spring trying to figure it out so my patience is kind of running out.

 

[Schrade]

First thing, unless you have made notes about the grounds that you've added - literal notes, I suggest removing them. If you forget what they are later, you're gonna' have even more problems...

If the dash lights and the temperature control lights start to flash at the exact same time, your solution will be easy to find, but finding the common circuit IN THE FSM will NOT be easy. You're gonna' need to find a ground circuit that grounds both readouts, and without the wiring diagram, it's a needle in the haystack.

See if you can borrow FSM from the local Chevy dealer...

 

[boomdriver]

First thing, unless you have made notes about the grounds that you've added - literal notes, I suggest removing them. If you forget what they are later, you're gonna' have even more problems...

If the dash lights and the temperature control lights start to flash at the exact same time, your solution will be easy to find, but finding the common circuit IN THE FSM will NOT be easy. You're gonna' need to find a ground circuit that grounds both readouts, and without the wiring diagram, it's a needle in the haystack.

See if you can borrow FSM from the local Chevy dealer...

One circuit that they share is the dimmer for the display lighting. Look at power supply connections and fusable links, as well as the G104 stack of grounds on the trans bellhousing.
Long shot would be the headlight switch.

 

[airman]

Found the problem

:L Back in the early spring I was trying to find a miss fire once the engine got warmed up,so I had bought a new capacitor with a new wire harness that goes from the ignition module. Well it did not plug in correctly,the black ground wire did not make good contact with the coil so it was trying to go to ground back through the computers. Everything is back working normal now, almost! I still have like a miss fire ever now and then when it is idling. But my radar detector goes nuts so I swapped out one out of my wife's car and it does the same thing. I'm going to pull the alternator and rebuild it,I hope that it is something to do with the charging system.

 

[boomdriver]

:L Back in the early spring I was trying to find a miss fire once the engine got warmed up,so I had bought a new capacitor with a new wire harness that goes from the ignition module. Well it did not plug in correctly,the black ground wire did not make good contact with the coil so it was trying to go to ground back through the computers. Everything is back working normal now, almost! I still have like a miss fire ever now and then when it is idling. But my radar detector goes nuts so I swapped out one out of my wife's car and it does the same thing. I'm going to pull the alternator and rebuild it,I hope that it is something to do with the charging system.

Pull spark plug wires one at a time until you find the one associated with the misfire. Then pull that plug and see if its wet, dark color, fouled or what. The cause may be the injector. If the ignition module was shorted it may now be damaged. Solid state modules don;t like inappropiate power or ground paths.
Electrical interferrence severe enough to mess with other things has to be very severe or a direct short. I have seen radiant interference in the wire harness cause misfire thru poor or diluted signal to the injector.

You could also be looking at the usual problem with Corvette electrical....grounds. There are many.

 

[airman]

New problem

ad Well now my gages work but the car will not run. It will start up and go dead. The vats has already been bypassed. I was able to pull some cades out last night before it started interupting the snapon scan tool. Codes are 31-33-35-37-54. If I turn the ignition on and leave it on everything starts cuting on and off fans ac compressor clutch and many others. Sometimes it will just shut off for a while and then start doing it again, I can slap the ecu and the will come back on. This is got to be the stupidist car I have ever seen. It is cutting power to the injectors and I sill have fuel preasure and spark. Any ideals?

 

[Schrade]

Did you remove the grounds that you added before? I think that is a starting point, if you really want to solve the problem. (ed.: I think the 54 is a computer code... If one of the 'computer grounds' that you added, was on a 5V PWM circuit, you might be in $light trouble. You should definitely remove them).

The radar detector might be 'reading' EMI radiation - same as a nuke, which will ALSO create false DTC's on solid state circuits. Mis-routed spark plug wires (wires out of the wire looms) will cause this, since they're high-energy circuits.

Were you able to get FSM from any local Chevy dealer? READ the diagnostic for each code, before doing anything, since any one code might say to check for another code FIRST. Solving one MIGHT solve all 4.

Do you have a multimeter?

When scanning, remember - if it's cold/open loop, some codes might not show up, not only not as H/history, but not at all.

 

[gmjunkie]

ad Well now my gages work but the car will not run. It will start up and go dead. The vats has already been bypassed. I was able to pull some cades out last night before it started interupting the snapon scan tool. Codes are 31-33-35-37-54. If I turn the ignition on and leave it on everything starts cuting on and off fans ac compressor clutch and many others. Sometimes it will just shut off for a while and then start doing it again, I can slap the ecu and the will come back on. This is got to be the stupidist car I have ever seen. It is cutting power to the injectors and I sill have fuel preasure and spark. Any ideals?

grounds,Grounds,GROUNDS Dude!~!! Clean and INSPECT ALL!~!! Including the crimp to the wire on eyelets!~!! Theres allot of them,Back of engine,above Oil Filter on block,below AC Housing rt side frame rail,Below H/L assys RT and LT frame rail,Behind Battery on frame to block,Behind Lt rear wheel on frame rail,there are a few inside the car too,usual places are under RT and LT Kick Panel,Rt and LT Lock pillar under carpet,Under Halo Trim Panel on inner steel reinforcement,Under rear hatch shelf by latch!~!!

 

[djsroknrol]

There is no code 31 for that year....very strange... code 33 is the MAF sensor circuit, code 35 is your IAC circuit. Those could account for your misfire. Again, there is no code 37 for that year, but code 54 is low voltage to the fuel pump circuit.....that could be something

could this be a low voltage issue? You would do well to have the alternator tested before you pull it, especially the regulator side as it might have been hammered.

I think you now have multiple problems, and to me it looks like you have the original problem along with a failure somewhere caused by that last grounding back.

May I ask, why did you change the ignition module wiring harness in the first place?

 

[airman]

Running good now

To clear up some confusion the codes I posted were from the CCU. I removed all the added grounds way on back. Today I bought a reman ECM and so far it is running better than it ever has sence I bought it,I just hope it keeps on. Thanks for the input.

 

[vetteoz]

Codes are 31-33-35-37-54. It is cutting power to the injectors

CCM code 54 is a fuel enable error which could explain that problem you had