1981 ecu
Thread Starter
Race Director
Joined: Oct 2019
Posts: 10,735
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From: Deep in the Pisgah National Forest
The connector being 180 deg out is normal. Not sure why it was done like that but it is.
The ECM grounds to two locations on the engine. One on the intake at the coolant outlet, one on the back of the passenger side head. (That's where they are on mine anyway). You should be able to find them by following the wires from the two 6 pin connectors on the passenger side.
A bad ground to the ECM could cause all sorts of problems.
There is a diagnostic chart to follow for no code 12 that i can post later but since you have a potential problem to solve first then I'll wait to see what you come up with.
The ECM grounds to two locations on the engine. One on the intake at the coolant outlet, one on the back of the passenger side head. (That's where they are on mine anyway). You should be able to find them by following the wires from the two 6 pin connectors on the passenger side.
A bad ground to the ECM could cause all sorts of problems.
There is a diagnostic chart to follow for no code 12 that i can post later but since you have a potential problem to solve first then I'll wait to see what you come up with.
One of the connectors had some crud on three of the pins, looked like undercoating. Cleaned it up and got good grounds at the correct terminals.
One of the battery bolts was rounded off and I had to use a plumbers pliers to remove it. Made new ones from my collection of ARP bolts.
I removed the ECU, picture of the label here:
And the PROM. I don't see 0075 anywhere.
Thread Starter
Race Director
Joined: Oct 2019
Posts: 10,735
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From: Deep in the Pisgah National Forest
I also cleaned up the test connector, getting to it by removing the seats and side carpet/ cardboard. Got a good ground there as well.
How the hell did some PO get a piece of hard candy in there?
Next step is to reinstall the ECU and battery and do the basic test again in post 9. Maybe tomorrow night.
Thanks everyone for your help here.
How the hell did some PO get a piece of hard candy in there?
Next step is to reinstall the ECU and battery and do the basic test again in post 9. Maybe tomorrow night.
Thanks everyone for your help here.
Le Mans Master
Joined: Jul 2000
Posts: 6,663
Likes: 162
From: columbia city in
I do not know how to set the timing on a 1981. I have only set the timing on a 1982.on a 82 you disconnect the one brown wire to the computer.you leave the 4 pin connector connected when setting the timing.If disconnecting the four pin is the proper way to set the timing then please ignor this post.
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
I do not know how to set the timing on a 1981. I have only set the timing on a 1982.on a 82 you disconnect the one brown wire to the computer.you leave the 4 pin connector connected when setting the timing.If disconnecting the four pin is the proper way to set the timing then please ignor this post.
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
I also cleaned up the test connector, getting to it by removing the seats and side carpet/ cardboard. Got a good ground there as well.
How the hell did some PO get a piece of hard candy in there?
Next step is to reinstall the ECU and battery and do the basic test again in post 9. Maybe tomorrow night.
Thanks everyone for your help here.
How the hell did some PO get a piece of hard candy in there?
Next step is to reinstall the ECU and battery and do the basic test again in post 9. Maybe tomorrow night.
Thanks everyone for your help here.
Thread Starter
Race Director
Joined: Oct 2019
Posts: 10,735
Likes: 63
From: Deep in the Pisgah National Forest
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
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Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,027
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
6084FN - M/t Fed (1st Des.)
9108OK - M/t Fed (2nd Des.)
5839CF - M/t CA (1st Des)
8014OJ - M/t CA (2nd Des)
6079FO - A/t Fed (1st Des)
8118OD - A/t Fed (2nd Des)
6092FR - A/t CA (1st Des)
8114OH - A/t CA (2nd Des)
Not sure what the difference is between the 1st and 2nd designs.
Race Director
Joined: Jul 2015
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From: SW Florida.
your first post you said it seems to be an unresolved issue. apparently you don''t need the ccc for emissions as it wouldn't pass without a cat. the reason it is unresolved is the ECU is a POS. if anybody repaired one, they would signal trace it and find-replace the faulty component. LEAVING THE REST OF THE 40 YEAR OLD COMPONENTS IN THERE WAITING TO FAIL!!! it was a bad design that barely worked to pass new emissions specs when new. they did not care how it would age. this setup is part of the reason all emissions stuff has to be warrantied for 10 years. take that ecu down to the river and float test it. return the distributor and buy a correct carb.
Thread Starter
Race Director
Joined: Oct 2019
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From: Deep in the Pisgah National Forest
In my opinion the emissions stuff that suck are the air pump and EGR. Since the catalytic converter is so old and the car has been running so rich, it is junk.
Emission controls that make a lot of sense and I absolutely will keep are the PCV and carbon canister systems.
No, this car doesn't have to pass emissions testing. Here in NC our State government doesn't penalize us for owning old cars. Anything 25 years and older is exempt. If its 35 years or older you can register it as an antique and it will be exempt from all inspections. Antique tagged vehicles also have a value of $500 or less for property tax purposes.
Emission controls that make a lot of sense and I absolutely will keep are the PCV and carbon canister systems.
No, this car doesn't have to pass emissions testing. Here in NC our State government doesn't penalize us for owning old cars. Anything 25 years and older is exempt. If its 35 years or older you can register it as an antique and it will be exempt from all inspections. Antique tagged vehicles also have a value of $500 or less for property tax purposes.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
In SC, whether to tax Antique Tagged cars is left to individual counties, some do some don't ... FloCo no tax Antique Tagged cars-trucks-mtc ... a pal has a couple warbirds ... $5 annually.
SC DMV charges a one-time fee to register&tag as Antique ... thereafter, no further annual reg-tag fee ... again, annual property taxes are left to Counties.
I got lucky ... SC antique tag issued some 15 years ago is black-on-gold and its gold background is a close match to '71 war bonnet yellow.
Defunct SC mandated Vehicle Inspection system WAS ineffective and corrupt ... it Ended nearly 25 years ago ... and, AFAIK never tested emissions.
Number 1 industry in SC is Agribusiness at some $47B; Forestry segment of that about $17B and some 70% of SC remains Forested ... on the whole, our air is quite good ...
... for as long as we can maintain a healthy balance, perhaps the nouveau snowflakes won't inflict vehicle smog regs & tests.
SC DMV charges a one-time fee to register&tag as Antique ... thereafter, no further annual reg-tag fee ... again, annual property taxes are left to Counties.
I got lucky ... SC antique tag issued some 15 years ago is black-on-gold and its gold background is a close match to '71 war bonnet yellow.
Defunct SC mandated Vehicle Inspection system WAS ineffective and corrupt ... it Ended nearly 25 years ago ... and, AFAIK never tested emissions.
Number 1 industry in SC is Agribusiness at some $47B; Forestry segment of that about $17B and some 70% of SC remains Forested ... on the whole, our air is quite good ...
... for as long as we can maintain a healthy balance, perhaps the nouveau snowflakes won't inflict vehicle smog regs & tests.
Thread Starter
Race Director
Joined: Oct 2019
Posts: 10,735
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From: Deep in the Pisgah National Forest
Finally got back at it. Cleaned all the connectors and grounded terminal 5, same as before, no Code 12, just constant flashing. I went through Chart 6 in Chapter 6E1 and got all the way to the bottom right "faulty ECM connection or ECM". Since I have no way of testing the connector I will replace the ECM.
In order to make the Chart 6 tests you either have to be a blind contortionist or do what I finally ended up doing: removing both seats, rear section of console (armrest), removing the battery to access the ECM, removing the ECM, then re-routing the ECM cables to the floor under the driver's seat. Then re-installing the battery.
A much better design IMO would be to mount the ECM under the driver's seat. It's a better environment for a computer that next to the battery, and I don't have to disassemble half the interior to test. I may build a bracket and do that once I get this working.
In order to make the Chart 6 tests you either have to be a blind contortionist or do what I finally ended up doing: removing both seats, rear section of console (armrest), removing the battery to access the ECM, removing the ECM, then re-routing the ECM cables to the floor under the driver's seat. Then re-installing the battery.
A much better design IMO would be to mount the ECM under the driver's seat. It's a better environment for a computer that next to the battery, and I don't have to disassemble half the interior to test. I may build a bracket and do that once I get this working.
Thread Starter
Race Director
Joined: Oct 2019
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From: Deep in the Pisgah National Forest
Code 12 achieved. Whoo hoo! Now I can put all the trim back (just refurbished the gauge pack) and figure out what is causing the check engine light to stay on.
Thread Starter
Race Director
Joined: Oct 2019
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From: Deep in the Pisgah National Forest
I fired up the car today after an extended period, let it warm up a bit then plugged in the four wire connector to the distributor. This raised the idle speed and smoothed out the engine, so I worked the throttle to get on the lowest cam to reduce the idle speed to normal. I did not check the timing but that indicates that the ECU is advancing the distributor correctly.
I took the car for a short drive and lo and behold, the check engine light shut off. Comes back on during idle. I'm thinking it's the O2 sensor, dirty from running rich for so long, and I'll test that, clean it next time.
Car runs OK under low RPMs, bogs down under higher. I'm guessing the catalytic converter is clogged. I intend to get rid of it along with the Y pipe altogether, and install an H or X pipe for a true dual system.
I took the car for a short drive and lo and behold, the check engine light shut off. Comes back on during idle. I'm thinking it's the O2 sensor, dirty from running rich for so long, and I'll test that, clean it next time.
Car runs OK under low RPMs, bogs down under higher. I'm guessing the catalytic converter is clogged. I intend to get rid of it along with the Y pipe altogether, and install an H or X pipe for a true dual system.
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
how long at idle before it comes on?
Thread Starter
Race Director
Joined: Oct 2019
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From: Deep in the Pisgah National Forest
Maybe if I can figure out how to avoid traffic lights this wouldn't be a problem.
Safety Car
Joined: Jul 2005
Posts: 3,682
Likes: 829
From: WI
81's didn't use a heated O2 sensor. It needs to be hot to create a mV. During idle they cool down and often the system goes into "Open Loop" till ya come off idle, and light can flicker. Or there could be a slight vacuum leak, or the throttle (carb) bushing could be worn. Pull the code and see. Code 12 is normal (means no dist ref signal -- normal when the car's not running). The factory service manual has pretty good troubleshooting trees. For anyone looking to really understand the CCC is to get GM training books SD-211 & SD-212 (ebay).
Here's a link on the print-out I did from a 81 Caprice last week:
https://www.corvetteforum.com/forums...t-example.html
.
Here's a link on the print-out I did from a 81 Caprice last week:
https://www.corvetteforum.com/forums...t-example.html
.
Last edited by Mark G; Mar 11, 2020 at 11:15 PM.