Yesterday on my '84 Trans Am, the 'check engine' light came on. She's got a mostly stock 305 LG4 engine. The light came on when I stomped on the gas from a stoplight. It's never happened before, and the car wasn't acting any different. I turned the car off and the light went away. This morning when I took off from a stop sign at about 3/4 throttle, the light came on again. When I parked and shut the car off, then started it again, the light went off. The same thing happened when I went back home. The car has been 'dieseling' a little when I shut it down from time to time, but I don't believe the timing is off and the car isn't running hot. Is this telling me my car is running lean, or the O2 sensor is bad, or is there a knock sensor on the thing that I don't know about? Can anyone help?

 

read the code, either get it read at a shop, or do the paper clip thing in the tech articles

 

O.K. but where do I find that 'DLC' connector?

 

First, you'll need to acquire a GM OBD I ECM Diagnostic Trouble Code Retrieval Tool (commonly known as a paper clip to TGO members).

With the engine and ignition turned off, locate the ALDL connector under the dash, just to the right of the steering wheel in the driver's foot well area. There should be a small rectangular cover over the access hole in the lower dash trim.



Insert a tool as described above (paper clip) into the 'A' and 'B' terminals on the ALDL connector:



WITHOUT STARTING the engine, turn the ignition to the "RUN" position. Watch the Malfunction Indicator Lamp (MIL) - it will begin to flash. This is also commonly called the "Service Engine Soon" or "SES" lamp. The first code will flash three times, and will usually be a code '12'. This is encoded by one flash of the lamp, a brief pause, then two successive flashes of the lamp. Each code will repeat three times, so you should see a "Code 12" flash three times. Any other error codes will follow in numerical order, and each code should flash three times. After all codes have been displayed three times, the "Code 12" will again flash three times, then all other codes will follow as described earlier. This cycle will continue until the jumper is removed or the ignition is turned off.

After you have made a note of all error codes, turn off the ignition and remove the jumper immediately. If you forget to remove the jumper and attempt to start the engine with it in place, you could damage the ECM. For this reason you should remove it immediately.

Once you have a note of all error codes, check this file for the decoding:

GM Error Codes.pdf.

(You'll need Adobe Acrobat Reader to view/print the file.)

 

Thanks Vader! I've got to tell you that you are the MAN! I mean that seriously. You've been helping out people here ever since I registered on this board. I don't want to run over at the mouth, I just want to say 'thank you' for all of your advice both to me and everyone else on this board.

O.K. the computer is giving me a code 34.
MAP sensor voltage high - pressure high/vacuum low
Is this just telling me I've got a vacuum leak somewhere? Where should I be looking?

 

Anyone help? Vacuum leak or what am I supposed to be looking for?

 

A bad throttle position sensor can cause that too... the ECM is confused because it thinks the vacuum should be high (since it's being told by the TPS that the throttle is closed) but it sees that the vacuum is low. If it comes on when you stand on it, I'd suspect the TPS. It's inside the carb.

You should rebuild the carb.

 

Well, today the light came on at a stop light as soon as I stopped. Could it still be the same sensor?