Misfire help.
#1
Misfire help.
I have a 90 with the FMII installed with a misfire that I can not solve. Its driving me crazy. The car starts and runs fine for awhile. Then the misfire starts during long drives usually after 30 to 40 minutes into it. Its like something is getting too hot and starts to miss. I've changed the plugs, wires, igniter and coil pack. Tried different heat range plugs and made sure they're gapped properly. I can smell unburnt fuel which leads me to believe its spark. I also check the ground wires which are fine. If I lets the car cool off its stops for awhile but then starts missing again. When its starts its sporadic but gets worse as you drive. Happens under throttle and while idling. Any help would be great. Thanks Brian.
#3
Its kind of hard to say. Before it starts it reads 14.8, 14.9. When it starts it bounces all over. It will go lean then right to rich but happens so fast I can't get a good read on the numbers. The misfires happen so fast it doesn't give the guage a chance to settle. I guess I could log it and know for sure.
#7
If we had a traditional crank trigger setup I would say its time to replace the crank trigger because the next step of this problem would be the car not starting when its just been running. But we don't have an internal crank trigger wheel and VR sensor and idk if the CAS shows the same signs at failure.
#9
bman, I've had a very similar problem with my car. It would start and run fine, then begin to stumble very violently at cruise speeds. Basically like the engine completely quit for a second. The RPM's on the guage would drop to zero for a split second. So an electrical problem somewhere.
I replaced the coil pack, which helped a bit, but the problem came back. Plugs, wires, grounding wires.
This was several years ago, and the car has sat (kids). Now I'm rebuilding the motor, and upon install I noticed that one of the wires to the CAS plug was broken at a connection. Looks like the install of the FM2 required this to be spliced, and my splice was failing. I'm betting that was the problem. Check that area really well.
I replaced the coil pack, which helped a bit, but the problem came back. Plugs, wires, grounding wires.
This was several years ago, and the car has sat (kids). Now I'm rebuilding the motor, and upon install I noticed that one of the wires to the CAS plug was broken at a connection. Looks like the install of the FM2 required this to be spliced, and my splice was failing. I'm betting that was the problem. Check that area really well.
#12
I'm assuming you are running a hydra but even if you not , Check your set up options and make sure the trigger and sync pull ups are enabled. We had something very similar happen on a friends Fm II . We spend weeks chasing a miss that would show up as soon as the car got hot. His car would start and run fine until it got hot and then it was almost undrivable. I think it had something to do with the resistance in that circuit increasing as things got hotter to the point that the signal was lost. Maybe someone that knows ECUs better can chime in one what exactly the pull ups do . Some thing to check anyways. Fred
#13
Thanks for the info Fred. I do have the hydra and that sounds just like the problem I've been having. I did check my setup options and the trigger and sync pull ups where not enabled. So am going to give that a shot. I also e-mail a trigger test and log to FM but yet hear back from them. I hope to get this figured out soon so I can go out and enjoy the car.
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