Good luck with that one!! 
1981 runs without computer / ecm?
Thread Starter
Racer
Joined: Nov 2011
Posts: 319
Likes: 12
From: South Chase WI
1981 runs without computer / ecm?
In the process of evaluating my recent buy, a 1981; it appears to be stock, air pump, lines, solenoid on the carb, etc. Did a vacuum line diagram check, many were on wrong / off etc but it still ran, just very rich at idle. The vacuum line re route seemed to resolve this, it now runs at an acceptable idle in gear and not. Auto trans. Trans does semm to drop into higher gear too fast unless you really foot it.
Check engine light only works if the ecm brown / white wire is grounded, no other time, not grounding the adl terminals, not on key up; so I figure bad ecm, right? I take it out, it's original. The PROM is in it, not loose.
The car starts right up with no ecm plugged in! Is this correct? The dist is all plugged in as well.....is it just running in a base mode, rich, awaiting the ecm to tell it to change?
My service manual is not here yet, does anyone have the test method / ohms at the ecm plug, to see what I've got? I do have a new ECM, but do not want to plug it in and let the smoke out of it right away.
Thanks all, great site!
Check engine light only works if the ecm brown / white wire is grounded, no other time, not grounding the adl terminals, not on key up; so I figure bad ecm, right? I take it out, it's original. The PROM is in it, not loose.
The car starts right up with no ecm plugged in! Is this correct? The dist is all plugged in as well.....is it just running in a base mode, rich, awaiting the ecm to tell it to change?
My service manual is not here yet, does anyone have the test method / ohms at the ecm plug, to see what I've got? I do have a new ECM, but do not want to plug it in and let the smoke out of it right away.
Thanks all, great site!
Last edited by maxmachz; Nov 28, 2011 at 07:31 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
The ECM has a "default" mode which sets a baseline operating strategy whenever the system cannot get the correct information from the sensors. Yes, it will run.....poorly. To get the kind of operation that the ECM system is capable of providing for you, that system will need to be operational, so that 'closed loop' behavior can be achieved.
The best advice I can offer is that you get a copy of the GM Chassis Service Manual for that model year. It has all the diagnostic information necessary to check out and adjust the engine management system. I know of no other manual that will provide all the info necessary to diagnose and repair your problem.
The best advice I can offer is that you get a copy of the GM Chassis Service Manual for that model year. It has all the diagnostic information necessary to check out and adjust the engine management system. I know of no other manual that will provide all the info necessary to diagnose and repair your problem.
3rd Gear
Joined: Nov 2011
Posts: 3
Likes: 0
the 81 I will not run with the ecu out of the car. I can only unplug one of the two connectors or it will die. I have a light on 24-7 key on engine off or key on engine running. I think there might be a short just havent figured out the issue yet. any insight on such issue?? thanks and sorry for getting off topic.
Instructor
Joined: Aug 2010
Posts: 233
Likes: 18
From: Monrovia Md
With no ECM plugged in the following will happen
1) The carb goes full rich at all times
2) the distributer goes into a test mode and will have no spark advance
Car will run really rich and be quite sluggish on acceleration, but should run and will idle fine.
Before you begin to debug the ECM, do you know that the carb and distributor are correct for the 81. Many people dropped the got rid of the ECM (even if it is still in the car) by changing the distributor and the carb.
Carb ID -- There will be two electrical connectors on the carb, one on the top, front, passenger side (Mixture solenoid) and one on the front drivers side (Throttle position sensor).
Dist ID -- There should be a 4 wire connector coming out of the drivers side of the distributor and NO vacuum advance diaphragm
There are a lot of people that can help you sort out an 81 on this forum. It is a unique year!
1) The carb goes full rich at all times
2) the distributer goes into a test mode and will have no spark advance
Car will run really rich and be quite sluggish on acceleration, but should run and will idle fine.
Before you begin to debug the ECM, do you know that the carb and distributor are correct for the 81. Many people dropped the got rid of the ECM (even if it is still in the car) by changing the distributor and the carb.
Carb ID -- There will be two electrical connectors on the carb, one on the top, front, passenger side (Mixture solenoid) and one on the front drivers side (Throttle position sensor).
Dist ID -- There should be a 4 wire connector coming out of the drivers side of the distributor and NO vacuum advance diaphragm
There are a lot of people that can help you sort out an 81 on this forum. It is a unique year!
Thread Starter
Racer
Joined: Nov 2011
Posts: 319
Likes: 12
From: South Chase WI
Very good info, yes it has the correct E4ME carb and distributor. Runs as described, with the ecm plugged in or on my kitchen table. Will wait for manual to test everything the right way before destroying my new ecm on first plug in.
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Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Yes, 81pilot...but, if I recall correctly, you pulled all the original engine control guts out and opted for a prior vintage carb & dizzy set up. We wouldn't want to mislead someone that yours is a 'normal' '81 engine and works fine without the ecm...would we?
Thread Starter
Racer
Joined: Nov 2011
Posts: 319
Likes: 12
From: South Chase WI
Ha! I read all of 81pilot's posts weeks ago, nice try though. I try to search on my issues and read up first, then post if I don't find what I'm looking for.
I'll get mine running prime WITH the right carb, ecm, dist, and sensors. I have all winter, by spring I will have this thing running smooth and quiet, getting the best fuel mileage possible when not having fun with my foot..... I will change the exhaust to a true dual no cat, and the air pump is off but carefully put away.
I'll get mine running prime WITH the right carb, ecm, dist, and sensors. I have all winter, by spring I will have this thing running smooth and quiet, getting the best fuel mileage possible when not having fun with my foot..... I will change the exhaust to a true dual no cat, and the air pump is off but carefully put away.
Instructor
Joined: Aug 2010
Posts: 233
Likes: 18
From: Monrovia Md
Keep the faith -- I love my 81 and the CCC runs great (it took a lot of luv, but its really not that hard). You will feel great when you understand, repair and get it all to work the way chevy intended. It is really a nice system for when and what it was.
There are a handfull of us that can help you get it sorted out. Before you took the ECM out, did you check to see if it reported any codes? Let me know if you need any help reading the codes or interpreting what they mean.
Good luck -- Bless the e4me!
There are a handfull of us that can help you get it sorted out. Before you took the ECM out, did you check to see if it reported any codes? Let me know if you need any help reading the codes or interpreting what they mean.
Good luck -- Bless the e4me!
Thread Starter
Racer
Joined: Nov 2011
Posts: 319
Likes: 12
From: South Chase WI
No light at all....checked the bulb, it was fine; grounded the brown / white at the ecm and the light lit up, so the ecm was getting power and the light and wire is good. Could not get codes because it is dead. I have a new ecm, have swapped the PROM, but don't want to install it until I can check everything else first. Waiting for manual to do just that, then we get ecm in, hopefully can pull codes and start the process of elimination.
Thanks for the offer, this site is great for sure. Hope fully I can help others in some way.
Thanks for the offer, this site is great for sure. Hope fully I can help others in some way.
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
No intent. I knew you would clarify it. It was directed to you. My apologies to the op if he was misguided. LOL
Last edited by 81pilot; Nov 29, 2011 at 10:27 PM.
Thread Starter
Racer
Joined: Nov 2011
Posts: 319
Likes: 12
From: South Chase WI
81pilot, your exhaust system....did you ever get the pics of the under the bumper area?
That is a must have, those straight pipes chrome slash cut. My pipes are getting a trip to the trash..... how'd you run the duals, right next to each other where the old single cat was? Mod the cross member or no?
Very nice, mine will have that by spring
That is a must have, those straight pipes chrome slash cut. My pipes are getting a trip to the trash..... how'd you run the duals, right next to each other where the old single cat was? Mod the cross member or no?
Very nice, mine will have that by spring
Drifting
Joined: Apr 2006
Posts: 1,911
Likes: 2
From: gold coast queensland
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
81pilot, your exhaust system....did you ever get the pics of the under the bumper area?
That is a must have, those straight pipes chrome slash cut. My pipes are getting a trip to the trash..... how'd you run the duals, right next to each other where the old single cat was? Mod the cross member or no?
Very nice, mine will have that by spring
That is a must have, those straight pipes chrome slash cut. My pipes are getting a trip to the trash..... how'd you run the duals, right next to each other where the old single cat was? Mod the cross member or no?
Very nice, mine will have that by spring
Burning Brakes
Joined: Oct 2011
Posts: 956
Likes: 86
From: McDonough Georgia
I have an 81. These are one of the best deals on the market today.
The CCC is an unwanted abomination. A horrid Frankenstein created by smog fanatics that lasted all of one year in production.
The good news? 81's are beautiful, plentiful and cheap. They are not collectible and are the perfect vehicle to customize. Anything you do is an improvement.
The car has low compression, less horsepower than a Honda and a pathetic TH 350 transsmission.
Pull off all the smog stuff, ditch the Rochester and dist. Then you can throw out the CCC. BUT, then the transmission won't lock up properly.
I have a 383 with Vortec heads and BW 4 speed. 81 is PERFECT for building your dream better.
The CCC is an unwanted abomination. A horrid Frankenstein created by smog fanatics that lasted all of one year in production.
The good news? 81's are beautiful, plentiful and cheap. They are not collectible and are the perfect vehicle to customize. Anything you do is an improvement.
The car has low compression, less horsepower than a Honda and a pathetic TH 350 transsmission.
Pull off all the smog stuff, ditch the Rochester and dist. Then you can throw out the CCC. BUT, then the transmission won't lock up properly.
I have a 383 with Vortec heads and BW 4 speed. 81 is PERFECT for building your dream better.
Thread Starter
Racer
Joined: Nov 2011
Posts: 319
Likes: 12
From: South Chase WI
How did you get your trans to shift right with that set up? Without a button you have to push?
Mine, it's fine the way it is, I can get plenty of tickets in it with all of those shortcomings.
If I want a power and speed thrill, I put my helmet on, get on my V65 Magna in the summer or my Mach Z in the winter and go 120 mph or more for as long as I want..........and in 10, 20, or 30 more years, when it's still all original, the 81 may be a collector, and I'll have one.
Mine, it's fine the way it is, I can get plenty of tickets in it with all of those shortcomings.
If I want a power and speed thrill, I put my helmet on, get on my V65 Magna in the summer or my Mach Z in the winter and go 120 mph or more for as long as I want..........and in 10, 20, or 30 more years, when it's still all original, the 81 may be a collector, and I'll have one.
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
A B&M Lock up controller device will lock the converter. As for the speed, I also have a Vulcan 2000 and it is plenty fast when I need it, but I am about ready to sell it to put the money in the Vettes new motor, I enjoy it more these days....I know Pete, I should not get rid of it.....and in 30 years I will be 78 and most likely won't care what I did to the 81, it is getting the treatment I want, not the next owner, I don't care what he thinks. 