Need help with misfire
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
Need help with misfire
I have a 1991 manual with the 6-speed. Its idling really rough, and when I try to drive it sounds like its running on two cylinders. It jerks terribly and makes an awful noise. However, it revs in neutral like nothing is wrong. The misfire is also not as bad above about 2,000 RPM as long as I keep the pedal light. Seems to be related to load. This problem came on very suddenly while I was driving.
I replaced the plug wires, and the ignition coil, as both were older than me. When I changed the coil it cleared for 10 minutes or so, then came back full force (I also tried a third coil which I found in my garage with no difference.) The coil has 12v on the battery cable. I have also checked the spark plugs, which are in great condition (they're pretty new). Cylinder #6 had some corrosion on the threads, enough to set it apart from the rest, but the electrodes were clear. The misfire also cleared once after removing a vacuum hose temporarily. But after I shut the car off it returned.
I also checked fuel pressure, which is a steady 40psi at all RPM. All injectors are clicking.
I've tried to find where the misfire is with an IR thermometer but have had no luck. All headers seem to be very close in temperature.
I'm not really sure what else to do. Anything is appreciated
I replaced the plug wires, and the ignition coil, as both were older than me. When I changed the coil it cleared for 10 minutes or so, then came back full force (I also tried a third coil which I found in my garage with no difference.) The coil has 12v on the battery cable. I have also checked the spark plugs, which are in great condition (they're pretty new). Cylinder #6 had some corrosion on the threads, enough to set it apart from the rest, but the electrodes were clear. The misfire also cleared once after removing a vacuum hose temporarily. But after I shut the car off it returned.
I also checked fuel pressure, which is a steady 40psi at all RPM. All injectors are clicking.
I've tried to find where the misfire is with an IR thermometer but have had no luck. All headers seem to be very close in temperature.
I'm not really sure what else to do. Anything is appreciated
Racer
Joined: Jul 2023
Posts: 256
Likes: 87
Was the vacuum sourced connected to the Fuel Press Regulator when you checked your fuel press? If Yes, the pressure should fluctuate a bit with on/ off throttle blips. It may be a bad FPR if it just stays at 40psi 🤔 good luck 👍
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
It was connected. How should it fluctuate? The needle did move a bit, but was always around 40PSI. I figured that it was designed to maintain about 40 pounds under all conditions.
There are no codes.
There are no codes.
