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Topic: Check Engine light on '81 help needed

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Re: Check Engine light on '81 help needed (2/12)
 12/1/14 5:47pm
Sarge81Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.


Joined: 12/3/2001
Posts: 2379

It would be best if Roy could find someone with a old OBD 1 scanner that shows live data. 
I kept my old '80-'95 GM OBD 1 scan tool that shows live data feed just for those occasional oldies that come by the shop. It takes the guess work out of it.

Now I'm just guessing at this. 
 It could be the ECM is failing or has a bad driver in it. It also could be a lazy O2 sensor, or dirt in the carburetor, float going bad, MC (metering control) solenoid going bad. 

If the O2 sensor looks original or has over 30,000 miles on it, I would change that out first. They are cheap and are technically part of a tune up on those cars from that era. 

Check the primary throttle shaft for slop. Grab the throttle linkage where the throttle cable hooks on to, try to move it front to rear or top to bottom and see it there is any play/slop. If so, the carb will have a vacuum leak possibly causing the ECM to put more fuel into the engine. 

Let us know what you come up with and we'll continue from there if needed.  


______________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


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Re: Check Engine light on '81 help needed (3/12)
 12/1/14 11:45pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

Thanx Darryl.Big smile
I suggested that he clean the corrosion off of the terminals on the ALDL connector, and try to pull codes again. It does kinda sound like the ECM is bad, but he needs to make SURE it will/will NOT pull codes. Seems like every time I've seen the problem of the Check Eng light not flashing codes, it has been a problem with the ECM, whether the PROM is bad/pins bent, or something else in the ECM is damaged. Also possible there is a wiring problem between the ALDL connector and the ECM....so many possibilities....Disapprove

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Joel Adams
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Re: Check Engine light on '81 help needed (4/12)
 12/2/14 7:25am
Sarge81Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.


Joined: 12/3/2001
Posts: 2379

If it does turn out to be a failing ECM, Roy needs to remove the PROM chip from his ECM and transfer it to the new one. Replacement ECM's don't come with a PROM chip. Hopefully it is the corrosion at the ALDL connector as you mentioned being the culprit for no blinking Check Engine light. 

Or if he want to rid himself of this problematic archaic system, just buy a non computer controlled HEI distributor and Rochester carb. Wink


______________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


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Re: Check Engine light on '81 help needed (5/12)
 12/3/14 1:07pm
rolasprint
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Thank you so much for your comments. Unfortunately I am in my final exams period and do not have the time to keep up with the car.

However I did order a cleaning spray for the contacts on the connectors and will try to pull the codes. But, as you say, I will order a o2 sensor and change it because the one that the car has seems old.

I also will search for slop in the carburetor and check if there is a vacuum problem.

Nevertheless I will also consider in replacing the ecm. Is it very difficult to do? I do not own a shop, only a craftman set and good will doing mechanics.

Thank you very very much.

Roy

ps: changing to a non computalized system seems like a great idea.

Re: Check Engine light on '81 help needed (6/12)
 12/3/14 5:40pm
Sarge81Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.


Joined: 12/3/2001
Posts: 2379

rolasprint said:Nevertheless I will also consider in replacing the ecm. Is it very difficult to do? I do not own a shop, only a craftman set and good will doing mechanics.

Thank you very very much.

Roy

ps: changing to a non computalized system seems like a great idea.



If it turns out your ECM is the problem, its easy to change. Your Craftsman tools will work fine. 
You'll have to remove the battery to access it. It's bolted to a bracket in front of the battery against the bulkhead. Once you get it loose, gently unplug the wiring harness from it. Then there is a small panel on the ECM that needs to be removed to remove the PROM chip for transfer to the new ECM. 

Good luck on your exams! 


______________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26
Re: Check Engine light on '81 help needed (7/12)
 12/17/14 3:14pm
rolasprint
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Hello Sarge and Joel, I finally finished my exams and got time to get my hands on the vette.

I changed the o2 sensor for a bosh one. The old one seemed to be very old. The results were as follow: car improved lightly, still feeling it a little "fat" but I feel as I have no fair judgment since it has been a while since I last drove it. But it definitely improved.

nevertheless, the check engine light is still on and I can not pull the codes. Cleaned the contacts with nail polisher and special contact aerosol.

I was thinking in reset the module to see if that clears the code and the light won't show no more. I guess that is be unplugging the battery, but for how long?

Other alternative I was considering is go ahead and change the ecm. When I bought the car, the alternator was overcharging the battery and gases really came out of it, maybe that produced some damage in the ecm since it is right next to the battery.

I could really use some advice as to which steps to take to identify the problem and solve it.

thank you so much for all the help.

roy 

Re: Check Engine light on '81 help needed (8/12)
 12/17/14 11:20pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
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Disconnecting the battery for 30-40 seconds will clear the code(s), and ECM memory. That will at least give you a clean slate starting place for further diagnosis.
An overcharging alternator can absolutely damage the internal electronics of the ECM. Depends on how high the charging voltage got, and for how long. Anything over 16v for very long will definitely fry it. 15v is pushing it.

______________

Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Re: Check Engine light on '81 help needed (9/12)
 12/18/14 11:11am
rolasprint
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Yeah, I will probably change the ecm and see if it fixes it and if not change the prom as well.

Now, I have seen some ecm and my best choice is a holley remanufactured one in 69 on ebay. I gues I will get the chip from summitR. What do you think?

Thank you very much.

Re: Check Engine light on '81 help needed (10/12)
 12/25/14 10:45am
rolasprint
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I ve finally fixed the problem.

By replacing the ECM with an ebay listed holley remanufactured $69 ECM and using the same prong not only does my car ride excellent but also the light is gone for good.

Thank you once more to all.

Merry Christmas.

Roy

Re: Check Engine light on '81 help needed (11/12)
 12/26/14 12:17am
Sarge81Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.


Joined: 12/3/2001
Posts: 2379

Awesome Roy! Glad it's up and running. Thumbs Up




______________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26
Re: Check Engine light on '81 help needed (12/12)
 12/26/14 8:15am
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

 Thumbs Up Clap Thumbs Up Clap
Have you already corrected the overcharging problem?


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Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

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