Prom ID changes when scanned

[mpick819]

Does anyone have any idea why my Prom ID would change during a real time diagnostic scan. I am using the auto x-ray 5000 and the ID changes about every 5 or 6 seconds
:confused

 

[Magmotor]

I've got an e-mail into a guy that's been using diag software for years. Will let ya know what he has to say about the changing number. Right off: I'd say it's the prom & not the ECM. Does the car run good at all or?? Usually when a scanner can't receive any data or can't connect to an ecm period, it means the ecm is no good. I don't think that's the problem in your case cause it's reading out info. I knew my ecm was bad when i had "Average mpg", "Instant" mpg, "Trip" od & "Range" readout as '0' on any or all the above.
I've never heard of anyone putting a '94-5 computer in an '86 but what the hey, ya learn something new everyday..

 

[mpick819]

There is a company that makes an esay install harness to convert the 94-5 PCM to the 86 vette. The harness costs about 400 dollars. The car runs fine most of the time, although I just sent the cluster off for repairs.
I am having trouble keeping the fuel mixture correct, and the car wants to fall on its face sometimes. I let it cool off and it is fine.
I have a custom chip for a 383 stroker that the guy I bought it from had put in.
Have been trying to find a shop manual so I can check all the grounds.
The car will be great eventually but it has been ignored way to much for a vette, if you know what I mean.

I redid all the vacuum lines already, replaced the oxygen sensors, and the temp sensor. I got bad readings for them, put the new ones and and still have bad readings

 

[vettenick]

What do you mean bad readings? Can you elaborate on what you scan tool read?

 

[mpick819]

Right now I have the dash cluster out and being rebuilt. I don't know whether I could do a scan or not.
But what I remeber is all of the reading indicated that it is burning rich, I never get a closed loop, the manifold temp is always negative and the rpm on the scanner changes constantly even when the car is idling
As soon as I get the cluster back I will scan it and download the results and make them available
Thank

 

[vettenick]

Closed loop means that the computer is in total control of the fuel delivery through the injectors. If you're in constant open loop, the computer is not getting the OK from the coolant sensor. The computer will be operating in a "fixed mode"and as a result you will be running richer than normal--not a good situation. There's one of two reasons for this: first, the thermostat is sticking open and the engine cannot reach operating temperture. Or something is wrong with the sensor, wiring, or the computer.
The fact that your air sensor is negative could be the result of an open circuit or a bad sensor. Either way, the computer looks at the coolant sensor to determine closed loop operation. What temperature does your coolant sensor read whan the engine is warmed up. A quickie check you should do before you start the engine is: when the engine is cold both the air temp and coolant temp should be almost the same (withina few degrees of each other) if not, there's something wrong with the sensors, wiring, or the computer. Let me know.