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Computer dead?

pdege

Member
Joined
Jul 23, 2006
Messages
8
Location
savannah, ga
Corvette
81 Beige coupe, no computer, '80 Beige coupe
I just purchased an 81, still waiting for the service manual. Previous owner removed all emissions stuff. While driving it home you could tell there was a miss that seemed very much like a timing issue.

Put the light on it to discover an initial timing at 22 Adv! Ran it up to 2100rpm and no further increase in the timing. The carb has no ticking sound. If I have to I'll go with a pre 81 dist and carb but I'd like to be sure that the computer is, in fact, dead.

The only mod I know of is the sticker from Crane on the air cleaner saying the cam is ok for use in Calif. The check engine light has been removed.

What should I test next?
 

Sensei

Well-known member
Joined
Apr 5, 2004
Messages
393
Location
Jacksonville, Fl
Corvette
'81 dark blue
First, I would re-install the check engine light (is it just the bulb missing?). Then you can check for trouble codes with a jumper wire. If you a need more detailed explanation of how to do this, let me know. If you would be up for a two hour drive, I've actually got the computer to check it here in Jacksonville. There may be a simple fix, but even if the computer is down, you can get them used for around $50, much cheaper than an aftermarket carb and distributor. God bless, Sensei
 

pdege

Member
Joined
Jul 23, 2006
Messages
8
Location
savannah, ga
Corvette
81 Beige coupe, no computer, '80 Beige coupe
Do you mean drive the vette there or put the computer in my dependable car and drive it down?
 

Sensei

Well-known member
Joined
Apr 5, 2004
Messages
393
Location
Jacksonville, Fl
Corvette
'81 dark blue
Unfortunately, it would have to be on the car. You can check trouble codes fairly easily though without the computer. Under your ash tray is the 5 pin ALDL. Once you have your check engine light working, use a metal paper clip to short the last two terminals on the right (D and E) together. The engine light will then flash once, pause and then flash twice (code 12, this one always flashes), it will repeat this 3 times, then it will flash any other trouble codes 3 times each. 52 and 53 are the bad ECM codes. Try this first and let me know what happens. God bless, Sensei
 

Sensei

Well-known member
Joined
Apr 5, 2004
Messages
393
Location
Jacksonville, Fl
Corvette
'81 dark blue
According to the description it would probably be right, but you might need to buy a chip ($120 for a performance chip at Autozone). First step, be sure that is the problem. God bless, Sensei
 

pdege

Member
Joined
Jul 23, 2006
Messages
8
Location
savannah, ga
Corvette
81 Beige coupe, no computer, '80 Beige coupe
Finally got the check engine light in. I jumped the 1st 2 contacts (the ones with no barrier between them) and nothing! The light just continually burns, no dots no dashes no code!!!
 

Sensei

Well-known member
Joined
Apr 5, 2004
Messages
393
Location
Jacksonville, Fl
Corvette
'81 dark blue
Disconnect the test wire and check for a blown ECM fuse.
If it still does not flash code 12 with a good fuse, ground terminal 5 on the ECM connector. If it flashes, repair the test lead to terminal 5.
If it still does not flash: disconnect the ground from term 5 and check voltage from terminals "C" and "R" to "U". See if they are over 9 volts or under.
These are the first steps on the diagnostic littany for your problem. If you get an original GM service manual (a must have for the do it yourselfer), the full chart is on page 6E1-16. The problem will be a bad connection somewhere or possibly a bad chip. If you do the above tests and still don't have the manual and have not found the problem, let me know and I will post the next steps. God bless, Sensei
 

xlr8shn

Member
Joined
Jun 29, 2006
Messages
22
Location
Ames, IA
Corvette
his: Blown 99 C5 Z51, hers: 81 Charcoal Metallic
I JUST replaced the ECM in my wife's 81. Bought the car for her last month. SES light was on, and jumping the ALDL retrieved nothing. Unplugging battery did not reset the SES light.

$87 for a rebuilt NAPA ECM and light went away and all is good... Car runs much better and no more light.

I did pick up an OTC 2000 scanner from ebay for future SES lights....

:cheers:
 

Sensei

Well-known member
Joined
Apr 5, 2004
Messages
393
Location
Jacksonville, Fl
Corvette
'81 dark blue
It's good to know the ECM is available from NAPA at a reasonable price, but I would be sure that is the problem before replacing it. It could well be as simple as a corroded multi pin connector at the ECM (it is right next to the battery, what a great idea that was!). You can fix it by just replacing parts, but it is an expensive way to go. I much prefer to trace the problem down and fix it right the first time. God bless, Sensei

P.S. The OTC Monitor 2000 is great, everybody with an '81 should keep their eyes on ebay and pick one up! (got mine for $25 a while back.)
 

xlr8shn

Member
Joined
Jun 29, 2006
Messages
22
Location
Ames, IA
Corvette
his: Blown 99 C5 Z51, hers: 81 Charcoal Metallic
I followed the troubleshooting tree in the manual...
 

pdege

Member
Joined
Jul 23, 2006
Messages
8
Location
savannah, ga
Corvette
81 Beige coupe, no computer, '80 Beige coupe
Well, I gave up. The service manual arrived and supported my decision. The car was highly modified by Bubba. No real additions but plenty of subtractions. Lots of wires with no terminals, broken terminals, or simply just cut. I traced what I thought I needed and neatly bundled the rest.

A '79 Qjet and a Summit non-computer dizzy and I am in business. It now runs just fine. Not sure just how the transmission was controlled but I know nothing about automatics.

Still looking for an '82 with low, low miles. Were 4 speed available in '82?
 

Yoda

Well-known member
Administrator
Joined
Oct 12, 2000
Messages
4,885
Location
Amarillo, TX
Corvette
1981 UL5
Sorry to hear of all the problems you are encountering with your 1981. Amazing isn't it how some folks can mess something up and actually believe they are "Fixing" it :eyerole ... Sounds like you are on the road and hopefully enjoying your :Steer ;)

Nope .... NO 4-speeds in 1982 all were Factory built Automatics ;)

Bud
 

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