Help! Check engine light on 81 vette

[BC-2011]

I am new to this site but i have use it and it is awsome. I bought a 81 vette 350 manual transmission for the wife(she always wanted one) Had to get it smoged well in the CA the check engine light has to work so i failed before i got in the door. I used this site with all the awsome support. I did all the things the posts said to do and ended up putting in a re-man ECM. The check engine light came on and when you started the car it went off GREAT all fixed. I had it smoged and the smog guy said it passed smog but the check engine light is on and we cannot get it to go off. The only thing he said he did was unplug the distrubitor plug with the engine running and the check engine light came on like its supposed to. He plug it back in tried to disconnect the NEG side of the battery to clear the code but it would not clear. I took it home jumped the plug under the ash try and it gave me a code of 15 and 55. I changed the temp sensor Code 15 and the 02 sensor code 55 and still the check engine light stays on. I cleared the code and still the check engine light stays on. I check the codes again and it still is giving the same codes 15 and 55. I have checked all the wires and they are good. The engine runs great with no problems. Any help i can get would be appreicated.

 

[bill81vette]

1st welcome to CAC! !!!
When I get home later this week,if nobody has answered your question about the codes I'll check them for you

 

[BC-2011]

Bill thank you...i think i know what the codes are i have read them on this site..excpet for the 55 code i have read two different things..I have read the 55 code is the o2 sensor and i have read another one saying it is the ECM so i replaced the o2 sensor but its still telling me the o2 sensor is bad and the check engine light stays on. I replaced the Temp sensor for code 15 but again the ECM is still giving me both codes and the engine light stays on. Any suggestion or help i can get would be great. I guess i could replace the ECM again just because its a new re-man does not mean a whole lot. Im frustrated because i thought i fixed it so i could smog it and after i smoged it the check engine light is on and it was working fine before i had it smoged. now i have more problems that i did before i smoged it...but again thanks..

 

[BC-2011]

Bill... This is a great site i found the correct codes in the CAC knowledgebase for the 81 vette. I guess it is both correct on code 55 it says o2 sensor or faulity ECM..so i guess i will try to get another ECM and see what happens... any other help or suggestion from anyone would be appreicated.

 

[SVO]

After you installed the O2 sensor, did you clear the codes from the computer? You should be able to clear the codes via a code reader or by un-hooking the a battery cable and waiting for 30 minutes before re-connectiong the battery cable.

 

[BC-2011]

I changed the Temp sensor and the o2 sensor un hooked the battery on the Neg side for about 30 minutes started it back up and i still have a check engine light and when i checked the codes again it still gives me the same codes 15 and 55. I tried to un hook the battery again to try to clear the codes again and i get the same thing. I guess the last thing to do is change the ECM again...thanks for the reply

 

[VetteV8]

Look at Rockauto; had just the same symptoms, and a new one was about 45$, but prices vary, depending what they have on stock.
It cured my problems completely.
Note, that there is a series of compulsory checks you must make on your car, before you install the new ECM, otherwise you could get the same defect back.
Cor

 

[BC-2011]

VetteV8...Thanks for the Info...do you know or can you point me in the right direction as to where i can find the compulsory checks you are talking about?

 

[VetteV8]

Those were included with the part: an instruction leaflet, which is likely not read, because it is so simple to install the new ECM; just plug in and go.
Don't do that , the checks are simple and explicit, if you would not get it with your set, I could scan and copy it here. After you have done the checks, and found something wrong, you must first correct that, a defective sensor for instance, or a short in a wiringloom.
Success.
Cor

 

[BC-2011]

VetteV8...I do not have those if you could scan them so i could do the checks that would be great Thanks

 

[VetteV8]

OK, here you go!

http://img.photobucket.com/albums/v631/vdl/ECM-test0001.jpg
http://img.photobucket.com/albums/v631/vdl/ECM-test0002.jpg
http://img.photobucket.com/albums/v631/vdl/ECM-test0003.jpg
http://img.photobucket.com/albums/v631/vdl/ECM-test0004.jpg

Just print them of, and put them in the right page sequence, fold in center...........
Just ignore the pencil marks; they related to my car, prior to installing the new ECM
Cor

 

[22229stingray81]

Did you check and clean the connectors? In my case I kept throwing codes, but the car ran fine. I sprayed some electrical contact cleaner in there, reseated the connectors, and the codes went away. Just a thought...


-Tatortot

 

[BC-2011]

VetteV8.... Thank you for the instructions you guys are awsome with all the help....I will try it before i install the new ECM...stingray 81.... Thank you for the help... I did do that the last time I put the new ECM in a week ago.... Im puzzled through all this...I installed the new ECM the check engine light worked like it is supposed to and NO codes thought I fixed it... But after it was smoged now all the codes...does anyone know if unplugging the distributor connector while the engine is running throw the ECM for a loop...that is the only thing the smog guy did and that is when the check engine light come on and now it is throwing all the codes...it was fine before that... I replaced the engine temp sensor yet it is still throwing that code and it won't clear... Right now it runs great even with the check engine light on...again thanks to everyone for all your help it is very much appreciated

 

[BC-2011]

VetteV8...i did the checks like the instructions said...when i checked C to B i got less than 20 ohms do you have any idea what sensor those two control...HELP... i dont what to put a new ECM in if its only going to fry it...or does that mean there is a short in the wire somewhere

 

[VetteV8]

When you look at my scan, you see, that I too got a value of less than 20 Ohms, namely 4,8 Ohms.
I verified this with my car wiring schematic, and found that there MUST be a value of less than 20 ohms; this has to do with the AIR pump operation, but since I wanted to remove that pump anyway, I just cut the wire to the AIR pump next to the ECM adapter.
In a way I am pleased that you too found this same thing, because you just confirmed my logic !!!!
There got to be an error in the leaflet.

There is no make or manufacturer on this document, but it came in a box prominently labelled
"Federal Mogul" and "Carter Fuel Systems ECM" printed on that box.
I meant to enquire about this "error", but never got round to it, the more because I cut the wire, and removed the AIR system already.
Also, my ECM now works fine, but I am pretty convinced that it would have with the low resistance reading which I measured.
Once again, you just confirmed that my interpretation of the Corvette wiring schematic was the right one.
What you do is up to you of course, if you have no problem code related to the AIR than you could just leave it;
I have no idea why you have the other codes again.............sorry
Cor

 

[BC-2011]

VetteV8...well im happy to report that all seems to be good..I put it all back together with the new ECM..(what's the worst that can happen beside let the smoke out of it) and it is working like it is supposed to NO CHECK ENGINE LIGHT it is working like it is supposed to...I had 8.1 OHMS when i jumped C To B and after you posted your response i put if back together... all other reading were good so i guess it is a miss print on the instructions but never the less i thank you for your quick responses and helping me through this problem....the car runs great and it seems to be fine..for now...again thanks to everyone for all the help...save the wave

 

[Peer81]

Great to see this problem is solved!

Greetings Peter

 

[berry1133@bellsouth.net]

I have a question in regards to the temp sensor. Is this sensor located on the right side of the engine block with two prongs sticking out? If so, are the wires that suppose to connect to it blue and black? If so let me know, if not help me with this one. I have what I believe to be the temp sensor sticking out of the block on the right side with no wires attached. Thanks.

BBerry

 

[bill81vette]

The temp sensor is on the right side head,with one prong sticking out.
between the back two cylinders.
I forget what color the wire is but it grounds itself elsewhere on the vette.

 

[Peer81]

The L81 has four temp switches.


In random order the first about the oil filter for oil temp. Second on the intake at the front, coolant temp for the ECM, third on the lift side between the first and second cilinder, coolant temp for the gaugecluster. And last is a original two prong temp switch on the right side between the two last cilinders, that one is for the aux fan. If I remember correctly yes the connectors are black and blue. Blue one is ground wire from the fan to the switch. As the old switch isn't self grounding the black wire goes from the switsh to a ground location at the transmission housing. When replacing the old (higher temp) switch for a new (lower temp) switch you'll get a one prong self grounding switch

Greetings Peter