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- #41
zzyzx
Steve
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Re: CEL - "random misfire" (recurring)
Ok, time for a possible helpful update on new findings.
I went out today to put more break-in miles on the Boss (at 980 now), and have figured out the exact conditions that throw the CEL.
In 4th gear @ 4000-4200 RPM (around 60 MPH) for about 10 seconds or more, causes the CEL to start blinking. Upshifting to 6th to bring the revs back down, and the blinking CEL goes away in about 5-10 seconds. At this point it either turns off, or stays on. If this is the first run after a code reset, the CEL seems to simply turn off. If you let the car sit for a hour or so, then go back out and reproduce the same behavior, the CEL stays on. All codes to date are just P0300.
I've paid close attention to all the various noises the Boss makes, and it's pretty obvious that right around 4000 RPM, the engine has some distinctly noisier harmonics at play. My guess is that this is what ultimately leads to the misfire detection.
Note that I haven't once actually felt anything when this happens; no hesitation, nothing.
The current engine in my race car also has a "noisy" region in the RPMs that has lead to false knock detection. The stand-alone engine management system has a sophisticated set of parameters to adjust that can help avoid these false positives. I had to datalog the sensor inputs and graph the raw knock sensor values against RPM to figure this out. Once identified, I adjusted the parameters to suit, which worked.
All that said, this doesn't necessarily reduce the possibilities of what could be the root cause, but it is great to now have identified a repeatable procedure to demonstrate to the Ford dealership as well as to do as an after-fix litmus test to confirm that the issue has been resolved.
Ok, time for a possible helpful update on new findings.
I went out today to put more break-in miles on the Boss (at 980 now), and have figured out the exact conditions that throw the CEL.
In 4th gear @ 4000-4200 RPM (around 60 MPH) for about 10 seconds or more, causes the CEL to start blinking. Upshifting to 6th to bring the revs back down, and the blinking CEL goes away in about 5-10 seconds. At this point it either turns off, or stays on. If this is the first run after a code reset, the CEL seems to simply turn off. If you let the car sit for a hour or so, then go back out and reproduce the same behavior, the CEL stays on. All codes to date are just P0300.
I've paid close attention to all the various noises the Boss makes, and it's pretty obvious that right around 4000 RPM, the engine has some distinctly noisier harmonics at play. My guess is that this is what ultimately leads to the misfire detection.
Note that I haven't once actually felt anything when this happens; no hesitation, nothing.
The current engine in my race car also has a "noisy" region in the RPMs that has lead to false knock detection. The stand-alone engine management system has a sophisticated set of parameters to adjust that can help avoid these false positives. I had to datalog the sensor inputs and graph the raw knock sensor values against RPM to figure this out. Once identified, I adjusted the parameters to suit, which worked.
All that said, this doesn't necessarily reduce the possibilities of what could be the root cause, but it is great to now have identified a repeatable procedure to demonstrate to the Ford dealership as well as to do as an after-fix litmus test to confirm that the issue has been resolved.