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Old 08-19-2012, 05:20 PM   #1
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Default 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.
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Old 08-20-2012, 09:55 AM   #2
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What does your wideband show before/during/after the misfires?
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Old 08-20-2012, 01:24 PM   #3
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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.
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Old 08-20-2012, 09:33 PM   #4
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Misfire at cruise, WOT, both?
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Old 08-20-2012, 09:45 PM   #5
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Ask genesplicer. He had a similar issue on his early na. Not turboed, but very similar time frame. His would actually die, then spontaneously start again. Yours could have the beginning symptoms of his issue.
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Old 08-20-2012, 09:51 PM   #6
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Both, the hole rpm range. Its start with a miss here and there but gets worse the longer I drive it. It gets to the point that its almost undriveable. If I let it sit and cool off for awhile it goes aways but starts back up after awhile.
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Old 08-20-2012, 09:55 PM   #7
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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.
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Old 08-20-2012, 10:13 PM   #8
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I had someone else on another forum say it could be the cas. I wish I could borrow one from someone that lived close by. I would like to know if thats what wrong before I go buy one. Kind of tried of just throwing money at it.
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Old 08-21-2012, 02:54 PM   #9
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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.
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Old 08-21-2012, 06:45 PM   #10
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The FM 2 kit I installed did not require a splice into the cas. I think I'll try to find a used one here locally and see if it makes the difference.
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Old 08-29-2012, 10:24 PM   #11
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I e-mail Fm today and they asked me to send them a log of when the misfire happens. They also asked me to do a trigger test. Being a newb to this I don't even know what a trigger test is. So can someone tell me how to do this without to much bashing. Ok a little bashing is fine.
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Old 09-05-2012, 05:56 AM   #12
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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
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Old 09-05-2012, 09:25 PM   #13
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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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Old 09-07-2012, 12:54 PM   #14
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Were you able to solve the problem ? FB
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Old 09-07-2012, 03:07 PM   #15
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No it didn't fix it. FM e-mailed me back today. They said it will be a week before they can look over the log I sent them and get back to me.
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Old 09-07-2012, 03:22 PM   #16
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My only other suggestion , would be to get a fresh base map from Jeremy and go though all the initial setup again. That way youd at least know if your chasing a hardware or a programming problem. Good luck I've been there too FB
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