Rumble Strips Causing Misfire

#1

I have had this issue on two seperate race weekends with perfectly working race weekends inbetween. At Memphis last season I was out in a practice session when I hit one of the high curbs and the car began misfiring and acting like it had a fuel cut/rev limit that wouldn’t let me go full throttle or build the revs. It was not gear dependent or RPM dependent persay but got more upset the closer I got to WOT. I gave it a lap with no improvement before I came back to the pits and checked every electrical connector I could think of and then went back out in the next session and the motor worked great the rest of the weekend, but I tried to avoid the big curbs.

Well it happened again 2 weekends ago at NOLA. It happened once when I hit the rumble strips at the exit of the final corner in a Saturday race where it stumbled but then came right back on the straight away. I was kind of low on fuel and chalked it up to that even though I ran another 4 laps or so and it didn’t do it again. Then on Sunday on the first lap of a race I hit the same exact rumble strip and it stumbled again but this time it never came back. I gave it another couple laps of seeing if it would come back before I hit the pits. While going slow in 2nd gear a check engine light lit up but then went away before I got to my pit and parked it.

It cost me a whole race this time, so I would like to figure it out. Unfortunetly, I haven’t tried just turning the ignition off and then back on while out on track to see if that remedies it or pulling my kill switch and the starting the car again. It definitely only occurs when hitting large curbs or very rumbly rumble strips. I have my coil bolted in place and all my relays zip tied in place. I do have the diagnostic port cover in place on the round connector in the engine bay. Can anyone think of anything I should check that could vibrate enough to piss off the ECU? I currently have my ECU ziptied to my roll cage dash bar, but I think I am going to rubber mount it to the floor board now.

#2

I had a similar problem for a while in 2009. I found it by wiggling everything electrical while the car was idling. I kept at it until I finally found something that made the idle sputter when I wiggled it. So that was the key. Just keep wiggling things until you can trigger the symptom.

Turned out, in my case, to be a frayed CPS wire that couldn’t be detected until I removed the sensor to get a better look at the cable.

#3

I had a very similar situation happen to me this last weekend at CMP. Car was running great until I had an off at the last corner before straight away and went into the rumble strips. For those that know these rumble strips can attest to the fact that they will rattle your brain pretty hard. As I came out of the corner the motor was just not coming up to speed. Very similar to your description. Did this for a lap or two and finally leveled back out and seemed to run OK. As I came into the pits after the race, the car completely died. All electrical was off as if my cut off switch had been turned. I quickly turned the cutoff switch off and then back on but still nothing. Got out of the car and went to look at my battery only to find the ground wire had come off the terminal and was resting against the post. Put it back on and all was good.

I am not suggesting it is your battery cable, but it could be a ground wire causing this situation after bumps.

#4

Ditto ranger. Happened to me at NOLA too. CPS was rubbing on a pulley and frayed it.

#5

Main relay tie wrapped?

#6

Test or jumper across the kill switch. I’ve had two go bad on me.

#7

I think the CPS wire and a ground wire are both great candidates. My car has all new factory plastic pieces that go on the timing cover to run the 6th cylinder signal wire and the CPS wire and protect them from the pulleys. I will check any ground wire I can find and try jiggling things.

I am not sure which relay is the main relay. I have the three on the driver side fender well zip tied into place. Because the issue only seems to happen on track and when hitting bumps I don’t know that I can just jumper the kill switch as wouldn’t that be against the rules. The kill switch appears to work fine as the car is running fine currently.

#8

Middle relay is main relay. Most forward relay is fuel pump. Rear relay is O2 sensor heater.

#9

In my experience, on what I believe to be cars in the OE configuration, the main relay is closest to the bumper, then the fuel pump relay, and finally the O2 heater relay. But since the sockets just clip into the holder, past work on the car can have them in any order.

#10

Check your coil harness.

#11

Check it for what? Loose connector?

#12

There could be broken solder connections on the DME. Open up the DME and check with a magnifying glass. They can be reflowed if you’re handy with a soldering iron.

#13

What if I go to the National/East/West Championship and they see the tool marks on my DME though? :dry:

#14

What if I go to the National/East/West Championship and they see the tool marks on my DME though? :dry:[/quote]
You tell them that you opened your DME to make sure there wasn’t some aftermarket chip inside. That’s something everyone should do.

#15

Good question. I don’t how NASA polices it, but I hope they do more than just look at the tabs on the DME to determine if a chip has been installed. Certainly if I’m ever questioned I will explain why I opened mine and offer to re-open it for their inspection. It takes minutes and I’ve got nothing to hide.

#16

Good question. I don’t how NASA polices it, but I hope they do more than just look at the tabs on the DME to determine if a chip has been installed. Certainly if I’m ever questioned I will explain why I opened mine and offer to re-open it for their inspection. It takes minutes and I’ve got nothing to hide.[/quote]

That was a joke about Nationals a few years ago where they came down with a rule saying that your ECU had to look like it had never been opened.