computer problems still

2_bamboo · Posted: Fri May 30, 2008 10:57 am Post subject: computer problems still

Ive got a check engine light on
its been in the shop numerous times to figure out why.
new computer
new lamp driver
new prom chip.
mechenic said hes getting a prom chip failure code.Prom chip has been changed twice

any and all help will be greatly appreciated

1985 elcamino
stock 305

Harald K · Posted: Fri May 30, 2008 2:34 pm Post subject:

The only way to properly diagnose a problem related to the computer control system is to perform a scan of the system. There are a number of scanners that can do a good job even Auto Zone will do a basic diagnostic for you free.
Also keep in mind when you extract the code with the scanner or the check engine light that just identifies the system and not necessarily a bad component a bad connection loose contact will show the failure code the same as a bad TPS or MAP. If you have already changed the items you have listed you can pretty well rule out your ECM. You did not mention how the car was running if the car runs well and you just have the light all the time it may be a simple ground not making good contact. If there is a problem with the performance of the engine then you should be able to flash a code by shorting the ADL which will direct you in the right direction. I know that since you are in good old politicly correct California you can't do this, but I have know a number of guys who have had check engine light issues where they car was running fine and they simply remove the bulb to the light. Any way I think with a good code reader or proper scan you will be able to isolate the problem better than by changing a bunch of part without a plan. Good Luck

2_bamboo · Posted: Fri May 30, 2008 6:48 pm Post subject:

Harald
the car isnt running that bad,actually pretty good but the gas milage dropped down real quick,and it smells like its running very rich

Harald K · Posted: Fri May 30, 2008 9:30 pm Post subject:

The electronic feed back carburetor system was the earliest computer controlled fuel system. The computer actually only controls spark timing and idle and not much more. If it appear to be running rich there are two things I would check the TPS throttle position sensor and the oxygen sensor, both of thes would set codes if they are the problem.

2_bamboo · Posted: Sat May 31, 2008 9:07 am Post subject:

Harald,
The thing is he tried to scan the codes,at first he couldnt read any codes because he said ther wasnt any showing.He found a broken wire in the computer harness and fixed that but it still wasnt getting much.He put a prom chip in from a 85 olds and his scanner started reading but he gets a code 51 which is prom failure.Even with a factory prom chip from gm he gets the prom failure.Im at witts end here.Im almost thinking theres a ground off somewhere like you said.Im gonna jump under the dash today and look around.Oh i forgot to mention the code reader or computer isnt picking up the oxygen sensor.

Dave

Harald K · Posted: Sat May 31, 2008 12:05 pm Post subject:

Since there was a broken wire that you guys repaired I would go back to square one put your original prom back in and start over. very likely the Olds prom would show an error since it is probably for the Olds 307 etc. Not sure what other parameters are different but don't assume all GM's are created equal. Before I changed over to TPI fuel injection I tried a couple of different Prom's one from an 81 Vette and one from and 85 Monte Carlo SS the Vette ran strong once it built RMP probably due to a wider spark curve but did not like the torque converter lock up sequence. The Monte Carlo SS worked very well all around. I strongly suggest that you down load some trouble shooting procedures which you can find on line. Computer cars are extremely sensitive when it comes to the wiring connections and as I said grounds, a loose connector within a plug can cause your problem but first you need to find the circuit that has the problem, for that you need to be able to extract the code. You did not mention it but does the light stay on all the time or does it flash , come on after the car is driven ?

2_bamboo · Posted: Thu Jun 05, 2008 9:55 am Post subject:

the light stays on as long as the car is running.

hel98 · Posted: Thu Jun 05, 2008 2:21 pm Post subject:

The lamp driver module may be shorted. Should be a small green plastic box located above or to the right of the glove box, tied to the harness. The ecm controls this to turn on the ck. eng. light. With the key off, disconnect the ecm. Turn the key on. If the cel stays off the problem is in the ecm or the wiring. If it stays on the problem is in the lamp driver or the wiring. Have you checked all the fuses? I would suspect the lamp driver or wiring since the ecm is new.

From an 86 manual. Lamp driver wiring

yellow wire to cel
black to ground
white green stripe to ecm
1 ign hot wire probably pink/black
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