TLDR at the bottom, appreciate any input from the TB hivemind.
Car is a 1985 760 Turbo, LH2.2 and EZK. I am diagnosing a slight misfire at idle and stalling when cold. When warmed up, the car runs just fine. When the car is cold, the symptoms are as follows:
- The ignition timing jumps between 15-20 degrees. The harmonic balancer is new, and there are no cracks to indicate separation.
- The car pulls low vacuum at idle even with all the leaks fixed.
- When applying throttle, if you let off the gas pedal too sharply, the car will stall. Restarts instantly. You can keep it from stalling by releasing the gas pedal very slowly.
This seemed to indicate an incorrect mixture being computed somehow.
I then did the following:
- Replaced the wiring harness with new due to other issues.
- Tested ignition/FI components per Brickboard's FAQ. Replaced Coolant temp and hall sensors since they were out of spec. Knock sensor is torqued to the correct 7 lb/ft
- Performed a vacuum leak test with compressed air. Found dozens of small leaks and fixed them.
- Re-set the base idle when cold. Symptoms still present.
I performed another leak test last night (pressure tester fits in the hose between MAF and Turbo), and I can hear another leak. I can only hear air escaping from somewhere on the passenger side rear of the head, where there are no vacuum lines I can see. I suspect the head to manifold gaskets are done.
TL
R- My question is this- I've had these gaskets fail before on other redblocks and its usually just a minor annoyance, but it is possible that the leak is so bad that the 02 sensor would get a false reading from it?
Car is a 1985 760 Turbo, LH2.2 and EZK. I am diagnosing a slight misfire at idle and stalling when cold. When warmed up, the car runs just fine. When the car is cold, the symptoms are as follows:
- The ignition timing jumps between 15-20 degrees. The harmonic balancer is new, and there are no cracks to indicate separation.
- The car pulls low vacuum at idle even with all the leaks fixed.
- When applying throttle, if you let off the gas pedal too sharply, the car will stall. Restarts instantly. You can keep it from stalling by releasing the gas pedal very slowly.
This seemed to indicate an incorrect mixture being computed somehow.
I then did the following:
- Replaced the wiring harness with new due to other issues.
- Tested ignition/FI components per Brickboard's FAQ. Replaced Coolant temp and hall sensors since they were out of spec. Knock sensor is torqued to the correct 7 lb/ft
- Performed a vacuum leak test with compressed air. Found dozens of small leaks and fixed them.
- Re-set the base idle when cold. Symptoms still present.
I performed another leak test last night (pressure tester fits in the hose between MAF and Turbo), and I can hear another leak. I can only hear air escaping from somewhere on the passenger side rear of the head, where there are no vacuum lines I can see. I suspect the head to manifold gaskets are done.
TL
R- My question is this- I've had these gaskets fail before on other redblocks and its usually just a minor annoyance, but it is possible that the leak is so bad that the 02 sensor would get a false reading from it?