81-No timing advance when revs increased
Thread Starter
Instructor
Joined: Nov 2006
Posts: 122
Likes: 0
From: TX
81-No timing advance when revs increased
UPDATE:
Problem solved. First, my timing did not vary off of the initial 6 BTDC. I have only had the car a few months, and have not been driving it while I painted it and installed a new interior. Engine was struggling to get any RPS's.
First, I found that the ECC fuse was missing. Installed a fuse, and the timing now will advance under computer control.
Second, still had no check engine light when ignition turned on. Removed the instrument panel, and found the check engine bulb had been removed.
Replaced the bulb, and now the check engine light comes on with the ignition, and goes out after the engine starts. NO codes. The car runs fine with the ECC, much better than it did with it turned off.
I have no idea what problem someone was trying to cure by turning off the ECC, and removing the check engine bulb.
Original Post:
I understand that it is the only year model with this particular carb/distributor setup, controlled by the ECM.
It has the stock carb and distributor.
The car drives, but feels underpowered.
The timing is set at 6 BTDC, and doesn't advance as revs increase.
The check engine light is not on, but I don't know yet if the bulb is burned out or not. The light does not come on when the ignition is turned on.
I don't think I can pull any codes until I can get a check engine light working.
Is there a quick way to get started, like maybe looking at the voltages on the 4 pin distributor connector that controls the distributor advance, to see if the ECM is working?
The car will run up to 70-75 with no problem, except the sluggish feel from lack of timing advance. Is this an indication that the ECM is working, and controlling the carb properly? I'm not sure if the ECM controls the carb mixture throughout the throttle range, or only at idle.
Where do I start??
Thanks,
Dennis
Problem solved. First, my timing did not vary off of the initial 6 BTDC. I have only had the car a few months, and have not been driving it while I painted it and installed a new interior. Engine was struggling to get any RPS's.
First, I found that the ECC fuse was missing. Installed a fuse, and the timing now will advance under computer control.
Second, still had no check engine light when ignition turned on. Removed the instrument panel, and found the check engine bulb had been removed.
Replaced the bulb, and now the check engine light comes on with the ignition, and goes out after the engine starts. NO codes. The car runs fine with the ECC, much better than it did with it turned off.
I have no idea what problem someone was trying to cure by turning off the ECC, and removing the check engine bulb.
Original Post:
I understand that it is the only year model with this particular carb/distributor setup, controlled by the ECM.
It has the stock carb and distributor.
The car drives, but feels underpowered.
The timing is set at 6 BTDC, and doesn't advance as revs increase.
The check engine light is not on, but I don't know yet if the bulb is burned out or not. The light does not come on when the ignition is turned on.
I don't think I can pull any codes until I can get a check engine light working.
Is there a quick way to get started, like maybe looking at the voltages on the 4 pin distributor connector that controls the distributor advance, to see if the ECM is working?
The car will run up to 70-75 with no problem, except the sluggish feel from lack of timing advance. Is this an indication that the ECM is working, and controlling the carb properly? I'm not sure if the ECM controls the carb mixture throughout the throttle range, or only at idle.
Where do I start??
Thanks,
Dennis
Last edited by fastcw; Sep 30, 2010 at 04:47 PM. Reason: Update on problem
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Although I have had many Corvettes, this is my first 81.
I understand that it is the only year model with this particular carb/distributor setup, controlled by the ECM.
It has the stock carb and distributor.
The car drives, but feels underpowered.
The timing is set at 6 BTDC, and doesn't advance as revs increase.
That's why it feels underpowered
The check engine light is not on, but I don't know yet if the bulb is burned out or not. The light does not come on when the ignition is turned on.
This is a good place to start- No CEL, you can't tell if the ECM is working at all.
I don't think I can pull any codes until I can get a check engine light working.
Not unless you have access to a scan tool
Is there a quick way to get started, like maybe looking at the voltages on the 4 pin distributor connector that controls the distributor advance, to see if the ECM is working?
The car will run up to 70-75 with no problem, except the sluggish feel from lack of timing advance. Is this an indication that the ECM is working, and controlling the carb properly? I'm not sure if the ECM controls the carb mixture throughout the throttle range, or only at idle.
Where do I start??
Thanks,
Dennis
I understand that it is the only year model with this particular carb/distributor setup, controlled by the ECM.
It has the stock carb and distributor.
The car drives, but feels underpowered.
The timing is set at 6 BTDC, and doesn't advance as revs increase.
That's why it feels underpowered
The check engine light is not on, but I don't know yet if the bulb is burned out or not. The light does not come on when the ignition is turned on.
This is a good place to start- No CEL, you can't tell if the ECM is working at all.
I don't think I can pull any codes until I can get a check engine light working.
Not unless you have access to a scan tool
Is there a quick way to get started, like maybe looking at the voltages on the 4 pin distributor connector that controls the distributor advance, to see if the ECM is working?
The car will run up to 70-75 with no problem, except the sluggish feel from lack of timing advance. Is this an indication that the ECM is working, and controlling the carb properly? I'm not sure if the ECM controls the carb mixture throughout the throttle range, or only at idle.
Where do I start??
Thanks,
Dennis
The ECM, after it's warmed up and in closed loop, controls timing and mixture. There's also a knock sensor that will retard the timing if it "hears" any detonation. It will also retard the timing if the fuel pump is ticking.
If you don't have one already, you need to get a factory service manual. Good investment for the CCC cars- they have procedures for troubleshooting and setup stuff for the carb . Haynes and Chiltons are ok for general stuff, but the FSM is the needed bible.
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
I assume that you used a timing light to check the spark advance, right?
If the check engine light does not light up at start then either the bulb is out or the CCC system is not working.
Need to put the CCC system into diagnostic mode, but is uses the check engine light to displays codes.
Another way is to see if the mixture control solenoid is moving or not. Do you know where this is?
If the check engine light does not light up at start then either the bulb is out or the CCC system is not working.
Need to put the CCC system into diagnostic mode, but is uses the check engine light to displays codes.
Another way is to see if the mixture control solenoid is moving or not. Do you know where this is?
