carb issues? 1981
Thread Starter
Safety Car
Joined: Sep 2009
Posts: 4,964
Likes: 28
From: Pittsburgh PA
carb issues? 1981
car starts right up, choke works, idles ok. let engine get warm and shut it off. and immediatly start it back up and the idle is a lil rough and low. keep it running with the accelarator and after about 1 min it smooths out and the idle returns to where it should be. will do this everytime i shut it off and start it back up. i dont hear the mc sol clicking all the time. should it click all the time? no codes
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The '81 C3 was the first year for an ECM system. Is yours still intact and working? If so, you should have a Check Engine Light that illuminates when your ignition key is turned to "ON" (not "START"). Then, when engine is started, that CEL should not be illuminated. If you never see the CEL symbol, your ECM system is not functional....OR the CEL bulb is burned out (or removed!).
We need to know if your engine is still using the original ECM system or if that stuff has been removed and re-configured like non-ECM engine.
We need to know if your engine is still using the original ECM system or if that stuff has been removed and re-configured like non-ECM engine.
Thread Starter
Safety Car
Joined: Sep 2009
Posts: 4,964
Likes: 28
From: Pittsburgh PA
The '81 C3 was the first year for an ECM system. Is yours still intact and working? If so, you should have a Check Engine Light that illuminates when your ignition key is turned to "ON" (not "START"). Then, when engine is started, that CEL should not be illuminated. If you never see the CEL symbol, your ECM system is not functional....OR the CEL bulb is burned out (or removed!).
We need to know if your engine is still using the original ECM system or if that stuff has been removed and re-configured like non-ECM engine.
We need to know if your engine is still using the original ECM system or if that stuff has been removed and re-configured like non-ECM engine.
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Brett Foote
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If the ECM system is working correctly, your CEL light should be illuminating (maybe intermittantly) when you have problems after restarting. If it does not come on, then your problem is likely a bad (or going bad) sensor on the engine....maybe a bad temp sensor.
For the ECM to throw a 'trouble code' on a sensor, it would need to be defective for a period of time. Yours may only read improperly after a start-up for only a few seconds. Such a problem might force the ECM to revert back to default mode and cause the engine to run poorly until the sensor recovers and puts ECM in normal operating mode.
At least, that seems plausible to me. You can try to download any captured trouble codes. If there are any, they might give you a clue as to what may be faulty. From the symptoms, it would not seem to be a 'serious' problem with the engine.
For the ECM to throw a 'trouble code' on a sensor, it would need to be defective for a period of time. Yours may only read improperly after a start-up for only a few seconds. Such a problem might force the ECM to revert back to default mode and cause the engine to run poorly until the sensor recovers and puts ECM in normal operating mode.
At least, that seems plausible to me. You can try to download any captured trouble codes. If there are any, they might give you a clue as to what may be faulty. From the symptoms, it would not seem to be a 'serious' problem with the engine.
Last edited by 7T1vette; Jun 29, 2015 at 06:12 AM.
Thread Starter
Safety Car
Joined: Sep 2009
Posts: 4,964
Likes: 28
From: Pittsburgh PA
If the ECM system is working correctly, your CEL light should be illuminating (maybe intermittantly) when you have problems after restarting. If it does not come on, then your problem is likely a bad (or going bad) sensor on the engine....maybe a bad temp sensor.
For the ECM to throw a 'trouble code' on a sensor, it would need to be defective for a period of time. Yours may only read improperly after a start-up for only a few seconds. Such a problem might force the ECM to revert back to default mode and cause the engine to run poorly until the sensor recovers and puts ECM in normal operating mode.
At least, that seems plausible to me. You can try to download any captured trouble codes. If there are any, they might give you a clue as to what may be faulty. From the symptoms, it would not seem to be a 'serious' problem with the engine.
For the ECM to throw a 'trouble code' on a sensor, it would need to be defective for a period of time. Yours may only read improperly after a start-up for only a few seconds. Such a problem might force the ECM to revert back to default mode and cause the engine to run poorly until the sensor recovers and puts ECM in normal operating mode.
At least, that seems plausible to me. You can try to download any captured trouble codes. If there are any, they might give you a clue as to what may be faulty. From the symptoms, it would not seem to be a 'serious' problem with the engine.
Burning Brakes
Joined: Nov 2013
Posts: 889
Likes: 13
From: Jax/St. Augustine FL
Im a former 81 owner, had the system fully in tact after I had to overhaul the entire thing.
You may want to check the MAP sensor, it too has a say to the ECM with the Dizzy and Carb for proper mixture, esp at Idle. There is an awesome tool you should get as an 81 owner, its an OBD1 scan tool specific for 81 owners..Called an OTC Monitor 85. I grabbed it on eBay for 20 bucks - best investment I made for my 81!! Tells you the dwell, mixture, if you have any codes, lots more...its awesome !..just look like the calculators we had growing up in the 80's
here is the video of how it works:
You may want to check the MAP sensor, it too has a say to the ECM with the Dizzy and Carb for proper mixture, esp at Idle. There is an awesome tool you should get as an 81 owner, its an OBD1 scan tool specific for 81 owners..Called an OTC Monitor 85. I grabbed it on eBay for 20 bucks - best investment I made for my 81!! Tells you the dwell, mixture, if you have any codes, lots more...its awesome !..just look like the calculators we had growing up in the 80's
here is the video of how it works: