Frustration with 87 coupe - idle/fuel problems
03-14-2012, 04:58 PM
#21
Instructor
Thread Starter
Member Since: Mar 2010
Location: Saint Louis MO
Posts: 130
Likes: 0
Received 0 Likes
on
0 Posts
Nice weather today means several tests on the car, and I think we may have found the main issue.
Using a compression gauge, we checked compression on each cylinder, and found the following results:
1 - 145
3 - 145
5 - 140
7 - 148
2 - 140
4 - 148
6 - 140
8 - 120 ***
Note each cylinder is almost the same, with the exception of #8. According to the service manual, this may indicate a bad piston ring. We added 3 squirts of oil to the cylinder, and re-checked. The result was compression that shot up to 140 immediately, like the others. On following tests, the compression was lower, like before - 90, jumping to 110, then 120, but no higher.
We have done the following recently - replaced distributor rotor and cap, and re-checked timing. Curiously, when using the distributor wrench to adjust the distributor, it seems to have no effect, both with the timing wire by the brake booster connected and disconnected... - we are worried that the distributor may be "one tooth off" in its installation, but since the distributor is seated correctly and the car starts, wonder if that could be the problem or not.
Recall that the original problem was a blown head gasket on the passenger side, near the #8 cylinder.
If the piston ring is in fact bad, we have reached the end of the road. Please provide feedback to help us confirm if that is the issue with the compression readings or are we missing something else.
-david
Using a compression gauge, we checked compression on each cylinder, and found the following results:
1 - 145
3 - 145
5 - 140
7 - 148
2 - 140
4 - 148
6 - 140
8 - 120 ***
Note each cylinder is almost the same, with the exception of #8. According to the service manual, this may indicate a bad piston ring. We added 3 squirts of oil to the cylinder, and re-checked. The result was compression that shot up to 140 immediately, like the others. On following tests, the compression was lower, like before - 90, jumping to 110, then 120, but no higher.
We have done the following recently - replaced distributor rotor and cap, and re-checked timing. Curiously, when using the distributor wrench to adjust the distributor, it seems to have no effect, both with the timing wire by the brake booster connected and disconnected... - we are worried that the distributor may be "one tooth off" in its installation, but since the distributor is seated correctly and the car starts, wonder if that could be the problem or not.
Recall that the original problem was a blown head gasket on the passenger side, near the #8 cylinder.
If the piston ring is in fact bad, we have reached the end of the road. Please provide feedback to help us confirm if that is the issue with the compression readings or are we missing something else.
-david
03-25-2012, 10:31 AM
#22
Team Owner
One thing you may want to look at (again) is a possible vacuum leak. There are some vacuum lines under the plenum that are plastic and given the age of the car and the fact that you most likely moved them around during the disassembly/assembly process, it's possible that one of the lines have become cracked or broken. Doesn't take much of a leak to cause idle issues.
Look at the lines under the TB and the EGR valve. Note that some of these line attach to "T" fittings. One small line (and a larger one) goes from under the plenum down to the EEC canister. The small line on my 87 is broken just above the valve cover and I think it's going to be a problem to find replacement pieces.
The one cylinder that shows low compression is something that you shouldn't focus on right now. The engine should run OK with that level of compression in that hole.
I would pull the distributor and re-install it. Make sure that the #1 piston is up on the compression stroke and that the timing mark on the damper is right at the 0 (TDC) mark on the timing tab. Install the distributor making sure the rotor is pointing at the #1 plug wire stud on the cap. Disconnect the tan wire, start the engine and set timing at 6 degrees BTDC. Re-attach the tan wire and go thru the process for setting TPS voltage. And as mentioned, check the plug wires so that they match the firing order. Get one plug wire off by one and the engine may run at higher RPM but idle will suck.
Look at the lines under the TB and the EGR valve. Note that some of these line attach to "T" fittings. One small line (and a larger one) goes from under the plenum down to the EEC canister. The small line on my 87 is broken just above the valve cover and I think it's going to be a problem to find replacement pieces.
The one cylinder that shows low compression is something that you shouldn't focus on right now. The engine should run OK with that level of compression in that hole.
I would pull the distributor and re-install it. Make sure that the #1 piston is up on the compression stroke and that the timing mark on the damper is right at the 0 (TDC) mark on the timing tab. Install the distributor making sure the rotor is pointing at the #1 plug wire stud on the cap. Disconnect the tan wire, start the engine and set timing at 6 degrees BTDC. Re-attach the tan wire and go thru the process for setting TPS voltage. And as mentioned, check the plug wires so that they match the firing order. Get one plug wire off by one and the engine may run at higher RPM but idle will suck.
