4 replies to this topic

[racer466]

The car runs fine for hour or so, then it completely starts misfiring, it's barely drivable.  You come in wait a while then it runs fine, for 10 or 20 laps then starts doing it again- its hit miss, but always once it's been driver hard for a couple sessions.   It usually idles ok, it's when you give it some throttle.  It's a new car for us, previous owner just used if for track days.  I pulled the fuel pump to maker sure the sock thing hadn't fallen off or there was something blocking - OK.  I hooked up a scanner and no codes.  So now I'm wondering if there's a faulty ground.  Can anyone point me in the right direction, checked and cleaned the one on throttle body and down by brake cylinder, and negative battery to bottom of frame.  Are there any others, and anything else I can check??

 

Thank you.

[ChrisA]

Could be the coil packs are shot. Get heat-soaked, resistance goes up and misfires start. Cool down and they are okay for a brief period. Though, could be a sensor dealing with heat soak. Electrical issues are often a real PITA to track down. I'd start with the coil packs and spark plug wires.

[bmarshall1]

I had a similar issue; bad cut out around 5k RPM if I recall.  It ended up being the crank sensor though.  It only did it as it heated up near the end of a race.  I also had a coil pack go bad but my symptom was the car only started on 2 cylinders.  After a few minutes it would start running on the other 2 cylinders and then be fine, go figure...

[Dan Twomey]

Cam position sensor harness.  Search it here.  Known issue with the 99.  Same thing happened with mine here a few weeks ago.  SCCA allows for you to solder in your own harness to help solve the problem for good.

[Carl]

This is a really unlikely solution, but it is super easy to check.  It has also been the source of problems for me twice (in two different cars) in the last few years.  Make sure the battery is not moving around allowing the positive terminal to ground intermittently. In the 99 it was grounding on the hold-down bar. 

 

Carl