ejcorvette

I have 81 vette and I have check engine light on. I tried to retrieve the code but for some reason the light would not blink and I even tried disconnecting my battery to see if it will go away...no luck! What do you guys think is wrong and how can I make it blink to get the code? Thank you in advance for all feed back.

a1sensei

I have an old OTC Monitor 2000 that reads the codes, but there is a way to short two of the terminals on the connector and make it blink the codes. I don't remember off hand exactly how to do this. If you tried this and it did not work, I would double check that you have the right proceedure. If you need me to, I'll look it up for you.

God bless, Sensei

Mark Hawkins

i have an 81 also. Does your car still have the computer (ECM). I'm new to the site, however, it sounds like you may not have the ECM connected. How is the car running, rich? I take it that you know where the ALDL connector is located, it is under the ashtray. Code 12 (one long and two short blinks) is the standard everthing is okay code. All you need is a flat head screw driver. I will help if you need some more info.

Mark (still a learning rookie)

maxmachz

First look behind the driver seat, in the battery area, and the ecm is right in front of the battery.
The connector under the ashtray, 5 terminals, from left to right A thru E....the 2 right most terminals, D and E are for diagnostic; the last one, E, being chassis ground. Touch these 2 together, D and E, with the key on, no engine running. Wait, it takes a few seconds, listen for clicking, light should begin to flash. If it stays on, use a wire to known chassis ground and touch it to the second terminal in from the right, D. See if it goes into diagnostic. If yes E is no longer grounded. Just use the test wire ground, or look for why E is no longer grounded, broken, corroded, etc.

If not, pull ecm out of bracket, leave plugged in, look closely at the plugs, they are labeled... and ground terminal "5" on the ecm plug (still plugged in). Also check for 12v+ on terminal "R" on the ecm, this is the power to it, should be continuous. Should go into diagnostic, code "12" 3 times, then your trouble code(s) after that. Let us know what you get.

Hope this helps.

ejcorvette

Ya I grounded the terminal and no blink.

ejcorvette

Yes I still have the ECM, no mods on this car and everything is stock. I noticed its a bit running rich lately. I disconnected the ECM next to the battery and light still on.

I know where the connector to get the code and I grounded the terminal to get the light to blink but no luck.

ejcorvette

I'll try this one when I get home.

thanks and I will let you guys know.

jr105

If you disconnected the ECM and the light is still on then it sounds like you have a short to ground somewhere between the light and the ECM. The light has 12V applied to it all the time and the light is lit by the ECM completing the path to ground. Check the wire from the ECM to the light for continuity to ground. If memory serves me correctly it is G on the ECM connector or B (2nd form the left) on the connector under the ashtray.

ejcorvette

Sorry for the mistyped, I disconnected the ECM and plug back in and still light ON. I checked for continuity between connectors (under ashtray) and connector on the ECM side and it was good. I'm assuming my ECM is bad because when I pulled it out and disconnected it, I can see that inside is corroded.

How much usually a ECM go for this car?

maxmachz

Not much. Get a new one, not used, and pull the PROM out of the old one to put in the new one. Just did mine, $100.

Maintenance free sealed battery is a must, the ones with caps that gas when charged / not maintained will corrode the ecm.

VetteV8

Had the same; light would stay on and would never blink, whatever I did.
Had the ECM tested in another car, and in that car also the light would not blink, but stayed on.
A new ECM resolved the problem.
Cor

ejcorvette

I finally replaced the ECM back in early January this year and its been good since till the other day. The check engine light came on and I pulled the code and it was code 51 which is bad PROM. Also my car is misfiring when its running on gear and hesitating, but when i put on neutral and floor it, it runs ok...no misfire.

So guys think the prom is causing it? Where can i get a new prom replacement?

1yy07

try k&b products.

Mark G

Have you tried removing the prom and re-installing it? There might be a bad connection on one of the pins. Make sure the battery is disconnected when you do it.

Mark G

RC81

Only prom I could find was from Hypertech.

commander_47

Zip Corvette seems to have the parts for about 300 to replace the ccu and the prom.

http://www.zip-corvette.com/GroupDet...2+Rebuilt+ECM&

Then again, the whole mess could be thrown out and the Rochester retuned for an increase in performance and much cheaper.

ejcorvette

I did removed it and reinstalled it but still runs bad when its on gear.

7T1vette

Now that you have changed the ECM, have you [again] tried to retrieve the trouble codes stored in the [new] ECM? You should do that.

And, if you still can't retrieve them, your PROM is likely defective.

Vette5.5

Know this is an older thread revived, but since you're talking 81', assume the car has an electronically controlled carburator. These carbs have M/C(mixture control) soleniods, that tend to go bad over time. There's rubber tipped metering rods in these that can harden and break off. Car will run ruff, and though a code. Alcohol infused gas certainly isn't helping things here.

7T1vette

It is an older thread, but the OP is still trying to resolve the problem.