1981 computer help
Thread Starter
Pro
Joined: Aug 2007
Posts: 645
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From: Mississippi
1981 computer help
Just recently purchased this car and it Cranks, idles and runs great. It is almost all original and I would like to keep it that way if possible. The only issues at this time are: At WOT at about 4000 rpm the car just shuts down like it runs out of gas. It will catch back up when you let off the gas. I was reading about the 1981 ECM on the forum and someone stated the ECM also controls the manifold pressure switch stating it is there so when you go to WOT the manifold pressure drops and releases lock up solenoid. Could this cause the shut down? Also I have included pictures to see if someone can tell if I have the correct carb and dizzy. The dizzy has no vacumn advance. I checked the timing today and it is set at 8 degrees at idle when you give it gas the timing advances like on any other car. Checked with a timing light. I was under the impression this distributor would not advance the timing when unplugged. As you can see in one of the pictures the 4 prong plug coming from the Dizzy is unpluged. When I plug it up it kills the engine immediately. Thanks for any replies. Mike
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
That looks like the original carb. The ECM has nothing to do with WOT operation except opening the power valve all of the way. It will not cause the symptom you describe. Most likely the fuel filter is dirty or the fuel pump, float valve, bypass, etc. is not right. It has something to do with fuel delivery.
Burning Brakes
Joined: Feb 2000
Posts: 763
Likes: 281
From: Middleton, Id
Your timing is set with that connector unplugged then plugged in when finished. I have mine set to 12 degrees btdc. Lockup solenoid is in the transmission. Looks to be the correct carb. As stated do the basics on fuel delivery first then let us know.
Drifting
Joined: Apr 2008
Posts: 1,992
Likes: 56
From: Antioch IL
That looks like the original carb. The ECM has nothing to do with WOT operation except opening the power valve all of the way. It will not cause the symptom you describe. Most likely the fuel filter is dirty or the fuel pump, float valve, bypass, etc. is not right. It has something to do with fuel delivery.
sound like it may be a fuel filter.
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
The carb is an E4ME one....correct for an '81.
With the ECM unplugged the advance is limited and there is no control of the primary metering rods...they are at full rich position. There is no power valve in a E4ME carb.
Do not mate the ECM connector with the engine running. Does engine start with ECM connected? If not, then check to make sure the ECM connector is on the ECM. ECM is located behind driver's seat, open battery door and look on the forward wall. That is the ECM. It may be bad. Good thing is that they are about $100. Bad thing is if the PROM in the EMC is bad, OEM is no longer available, have to go aftermarket of which last I checked there was only one part available...another $80.
I have a spare OEM ECM with OEM PROM that I may be able to loan to you if you cannot find one. I keep one as a spare even though the rebuilt one I have had for over 10 years with zero problems.
With the ECM unplugged the advance is limited and there is no control of the primary metering rods...they are at full rich position. There is no power valve in a E4ME carb.
Do not mate the ECM connector with the engine running. Does engine start with ECM connected? If not, then check to make sure the ECM connector is on the ECM. ECM is located behind driver's seat, open battery door and look on the forward wall. That is the ECM. It may be bad. Good thing is that they are about $100. Bad thing is if the PROM in the EMC is bad, OEM is no longer available, have to go aftermarket of which last I checked there was only one part available...another $80.
I have a spare OEM ECM with OEM PROM that I may be able to loan to you if you cannot find one. I keep one as a spare even though the rebuilt one I have had for over 10 years with zero problems.
Thread Starter
Pro
Joined: Aug 2007
Posts: 645
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From: Mississippi
Thanks for the help guys. I have a bad battery or my altenator is bad. I noticed when I drive it for a while that is when I was having what I thought was a fuel issue but it is the battery getting low. I can charge it up and the car rus at WOT with no issues. Any ideas why the low battery would cause this?
I hooked up the 4 prong wire going to the dizzy and it will not start. If you look at the picture of the 4 prong from the dizzy someone put one of the blue splicers on it. The type that connects 2 wire together. Any idea why they did this? Anyway I removed it but it still will not start with it plugged up. I thought the timing advance was controlled by the ECM but as I rev the car my timing is advancing with the 4 prong unhooked. Is it also mechanical advance? It is definately getting poor gas mileage and I think it is running rich at idle also. It does start and run good. Thanks for the help as I would like to get it back to factory specs. Mike
I hooked up the 4 prong wire going to the dizzy and it will not start. If you look at the picture of the 4 prong from the dizzy someone put one of the blue splicers on it. The type that connects 2 wire together. Any idea why they did this? Anyway I removed it but it still will not start with it plugged up. I thought the timing advance was controlled by the ECM but as I rev the car my timing is advancing with the 4 prong unhooked. Is it also mechanical advance? It is definately getting poor gas mileage and I think it is running rich at idle also. It does start and run good. Thanks for the help as I would like to get it back to factory specs. Mike
Thread Starter
Pro
Joined: Aug 2007
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From: Mississippi
Hi and thanks for the responses. Today I tried to check for fault codes but when I grounded the 2 terminals under the ashtray I could not get the check engine light to come on. If the ECM is bad would the check engine light still come on? The check engine light has never been lit since I have had the car. Any way to check and see if it even comes on to make sure the bulb is not blown? Thanks, Mike
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Drifting
Joined: Apr 2008
Posts: 1,992
Likes: 56
From: Antioch IL
Mike, when you turn the ignition switch on the check engine light should turn on. If it does not turn on then the bulb maybe burnt out.
this may also help
this may also help
Last edited by larryg3; Mar 7, 2013 at 08:30 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
You should disconnect and clean all the computer connectors and any connectors on engine sensors; also clean the ground line(s) for the ECM. Put some dielectric grease on all connector terminals before hooking them back up. Then, try it again. All those metal connector terminals will corrode over time and the ECM is sensitive to that. If you clean all the electrical connections, verify you have good 'ground', and run the codes to find no CEL again, the ECM is likely to be defective.
The best diagnostic document for that car is the 1981 Chevrolet Chassis Service Manual. It has tests to check the various system components and to troubleshoot the system.
The best diagnostic document for that car is the 1981 Chevrolet Chassis Service Manual. It has tests to check the various system components and to troubleshoot the system.
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
Oh comon' now.....what fun is that! It is a challenge to get the CCC to work.
If the Check Engine Lite bulb does not lite when ignition is switched on, then either the bulb is bad or the ECM is really dead. Going to have to pull the gauge panel off to get to the CEL bulb.
As far as igntion advance, yes there is some advance in the 7 pin module within the distributor, just not full.
Running rich at idle is due the primary needles being a full rich positon.
The battery not charging is why the car does not run very well, battery runs out of charge pretty quickly. Need to check alternator output and fuseable links. Alternators come in two sizes, regular or heavy duty and are interchangable, just different physical sizes.
The carb will likely need to be rebuilt at some point; let me know, I have done several...not hard, just requires a few special tools. All the info is in the Service Manual.
If the Check Engine Lite bulb does not lite when ignition is switched on, then either the bulb is bad or the ECM is really dead. Going to have to pull the gauge panel off to get to the CEL bulb.
As far as igntion advance, yes there is some advance in the 7 pin module within the distributor, just not full.
Running rich at idle is due the primary needles being a full rich positon.
The battery not charging is why the car does not run very well, battery runs out of charge pretty quickly. Need to check alternator output and fuseable links. Alternators come in two sizes, regular or heavy duty and are interchangable, just different physical sizes.
The carb will likely need to be rebuilt at some point; let me know, I have done several...not hard, just requires a few special tools. All the info is in the Service Manual.
Last edited by LannyL81; Mar 9, 2013 at 06:26 AM.
Thread Starter
Pro
Joined: Aug 2007
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From: Mississippi
Thanks Lanny, Bad battery and will be replaing it today. PO said carb had just been rebuilt. Who Knows but the gaskets do look new. I checked the ECM fuse and have power to both sides of fuse. Every thing that has to do with the ECM seems to be hooked up except the 4 pin prong to the dizzy. I still cant get the Check engine light to come on anytime. Next step is to pull center dash and check bulb. I do hope to get the computer working as factory. If I can get the check engine light to function I may purchase a ECM form autozone. Checked today and they are around 80 dollars. Could be that is the only problem as the 4 pin from the dizzy looks very clean inside the connectors telling me it has been unplugged recently. Thanks, Mike
Le Mans Master
Joined: Feb 2011
Posts: 5,943
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From: Southern NH
When i bought my '81 the CEL bulb was burnt out. When you unplug the distributor to set the timing, the light will come on until you plug it back in if everything is working fine.
My '81 is the first CCCarbed vehicle i have owned. And it runs 100x better then all my other carburetored cars put together.
My '81 is the first CCCarbed vehicle i have owned. And it runs 100x better then all my other carburetored cars put together.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
When you unplug the dizzy, it sends the computer into "default" mode and to an 'open loop' status where a base operation program is used...rather than closed-loop operating with O2 and other sensors and actually managing the ignition and fuel flow. The system will operate...rather poorly for performance and economy...but will function, nonetheless.
Check the CEL bulb and/or replace it to see of you can get it working. When you are in there, also check for power to the bulb [when ignition is set to ON...not START] to eliminate that possibility. With power and a new bulb, it should work--either sporadically or ON the entire time. If the bulb still stays OFF, the ECM is likely to be 'toast'. New replacements are readily available for reasonable money.
Also, if you can get the CCC system up and running properly, you will be better off than just trashing the CCC and sticking another carb & dizzy on your engine. Just my .02.
Check the CEL bulb and/or replace it to see of you can get it working. When you are in there, also check for power to the bulb [when ignition is set to ON...not START] to eliminate that possibility. With power and a new bulb, it should work--either sporadically or ON the entire time. If the bulb still stays OFF, the ECM is likely to be 'toast'. New replacements are readily available for reasonable money.
Also, if you can get the CCC system up and running properly, you will be better off than just trashing the CCC and sticking another carb & dizzy on your engine. Just my .02.
Last edited by 7T1vette; Mar 8, 2013 at 02:04 PM.
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
Thanks Lanny, Bad battery and will be replaing it today. PO said carb had just been rebuilt. Who Knows but the gaskets do look new. I checked the ECM fuse and have power to both sides of fuse. Every thing that has to do with the ECM seems to be hooked up except the 4 pin prong to the dizzy. I still cant get the Check engine light to come on anytime. Next step is to pull center dash and check bulb. I do hope to get the computer working as factory. If I can get the check engine light to function I may purchase a ECM form autozone. Checked today and they are around 80 dollars. Could be that is the only problem as the 4 pin from the dizzy looks very clean inside the connectors telling me it has been unplugged recently. Thanks, Mike
Be careful with the gauge cluster removal. There is a flexible printed circuit board that has a large connector plugged into it....remove this connector with care so as to not tear the contacts. Of course new "flex" is available...will cost $100 or so.
Expecting to read that CEL bulb is out, and that you will need to replace ECM and PROM. Getting the ECM out is a lesson in working with a mirror and flexability....any kids around that you could have crawl into the luggage area?
Keep the thread going with what you find.
Burning Brakes
Joined: Oct 2011
Posts: 956
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From: McDonough Georgia