1980 Corvette engine light
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1980 Corvette engine light
Ok I finally got the CEL working, I ground the test terminal at the computer and get what looks like three flashes on the CEL. if I hold ground on the test terminal, it will repeat this. So hoping someone can help me decode what the three flashes is trying to tell me is wrong. Rusty
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The 12 code flashes to indicate that the diagnostic system is functioning properly. If you keep it grounded, it should flash the 12 code 2 more times, then after a longer pause, it will then flash any fault codes stored in the computor.
The fault code will flash in the same manner as the 12 code. So if you have a 33 code in the system, you will get three quick flashes, a pause and three more flashes. The fault code will then repeat 2 more times. If there is more than one code stored, the codes will flash in numerical order, starting with the lowest numerical code. All codes will flash 3 times, before flashing the next code(s).
You most keep the terminal grounded for the fault codes to flash.
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ok cool I will go and see what code it is telling me because the engine light stays on so, at least it seems that the comp is working going to go look at it now
Last edited by Rusty-one-1; Mar 19, 2011 at 07:44 PM.
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It apparently means that there is a manifold air temp sensor in the system and it is not working. Go to NAPA and ask them if they can get one and show you on a diagram where it's located. Change it out and your car should work...better. Be aware that, right now...with that sensor not working...the engine is running so badly that the ECM might not be able to determine if anything ELSE is not working right, either. So, when you fix that sensor, fire up the car and let it fully warm up, cycle it through the gears, then look to see if the CEL comes on again. If it does, do the trouble code download again. It may come up with one or more 'new' codes...now that the engine is actually running!
In any event, your ECM is working properly (so far, anyway), so all is NOT lost. In fact, you may have found a relatively simple fix to your problem.
P.S. Thought of something else you should check... You should first test (check out) any wiring from that air temp sensor to see if that is why the computer isn't getting the temp data. The ECM doesn't know why that data is not present...just that it isn't there. Bad wiring would 'read' the same as a bad sensor.
In any event, your ECM is working properly (so far, anyway), so all is NOT lost. In fact, you may have found a relatively simple fix to your problem.
P.S. Thought of something else you should check... You should first test (check out) any wiring from that air temp sensor to see if that is why the computer isn't getting the temp data. The ECM doesn't know why that data is not present...just that it isn't there. Bad wiring would 'read' the same as a bad sensor.
Last edited by 7T1vette; Mar 19, 2011 at 09:42 PM.
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Were did you get this information? My Corvette Shop Manual shows code 23 as an "Open or Grounded Mixture Control (M/C) Soleniod Circuit", not a Manifold Air Temperature Sensor. I took this from the 1981 Corvette Shop Manual, but I think the codes for all 80-82 GM cars to be the same.
The Mixture Control Soleniod was part of the carburetor. The M/C Soleniod changes the air/fuel mixture to the the engine, by allowing more or less fuel to flow through the carburetor. The Mixture Air Temperature (MAP) Sensor does basically the same thing, it monitors incoming air and changes the fuel mixture accordingly, but it's a sensor in the intake manifold, not the carb. Did the 80 Corvette have a MAP sensor, I don't see a listing in my Corvette Parts Book?
Below is the page from my Corvette Shop Manual on the diagnostic procedure for "Trouble Code 23 M/C Soleniod Circuit".
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Same strategy applies...just on a different component. That mixture valve/solenoid is a one-year-wonder in the Q-jet carb that may be difficult (or impossible) to locate. If you need to replace it DO NOT throw the old one away until you locate a good replacement and actually fix your problem. If that old component is not totally "toast", perhaps it is possible to get it rebuilt, so keep it "just in case". {For example: If the failure is due to a solenoid winding problem, a good electrical shop can rewind the coil without too much problem.}
Again, the problem with the mixture control unit could be wiring related or connector/contact issue, rather than with the mechanism itself. The Chevrolet Chassis Service Manual for 1980 has procedures for testing that unit for proper operation. If you don't have a copy, see if someone can reprint those particular pages for you. Good luck.
Again, the problem with the mixture control unit could be wiring related or connector/contact issue, rather than with the mechanism itself. The Chevrolet Chassis Service Manual for 1980 has procedures for testing that unit for proper operation. If you don't have a copy, see if someone can reprint those particular pages for you. Good luck.
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Hmm well shoot,, I was all prepared to call Napa, Kragen, Autozone, whoever to try to find this man air temp sensor. But this almost makes more sense, the Carb seems to be running full rich and is part of why the numbers were so high at the smog shop. I did stumble on a 1980 olds cutlass LS in the junk yard yesterday, while looking for my impossible to find AIR diverter valve. This car seemed to have the same carb with the same connections. Pick and Pull wants 45 bucks for a 4 barrel carb, but was reluctant to get an old beat up carb like that from the junk yard with all the same problems. Rusty
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For the older C3's, there were two manuals: a Chassis Service Manual and a Chassis Overhaul Manual. GM may have combined them into one manual for later years...but I'm not in 'the know' on that one. Who has the GM reference manual(s) for 1980? 
Oops! You beat me to it, Glenn...
Oops! You beat me to it, Glenn...
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Go with the nice $25 one. As I told you in the PM, new ones go for $110.00, so $25 is a good deal! You'll get it greasy enough, so start with one you can read. The 80 Shop Manual will give you instuctions on how to diagnose problems, and repair them. It will also give you illustrations of most of the ECM and emission parts that your dealing with, and trouble shooting illustrations, like the code 23 one I posted earlier.
Last edited by gbvette62; Mar 20, 2011 at 03:03 PM.
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Go with the nice $25 one. As I told you in the PM, new ones go for $110.00, so $25 is a good deal! You'll get it greasy enough, so start with one you can read. The 80 Shop Manual will give you instuctions on how to diagnose problems, and repair them. It will also give you illustrations of most of the ECM and emission parts that your dealing with, and trouble shooting illustrations, like the code 23 one I posted earlier.