6.4L Rolling Idle @ Start & Stalling

Keith Browning · November 20, 2009

This one was potentially going to go wayyyyy off track but we were on our toes today. This F550 would start and immediately the idle would roll from 300 to 800 RPM for 5-10 seconds and then straighten out. It also was reported to stall after stopping, the tech verified that once.

DTC's P20e2, P0297 & P1000. Fuel pressure 6+ psi. Passes self tests. The tech corrected the P20E0 by replacing EGT 1-1 but the rolling idle remained. We suspected the HPFP and I recommended pinpoint tests M and perform the high pressure fuel system test. The fuel pressure test would not initialize and the error message said to release the throttle. No APP DTC's - so we started Data Logger looking at fuel and APP pids. We noticed that the APP MODE PID showed "PT" but all of the other APP pids indicated closed throttle. I pulled up on the pedal and the symptom went away. So we played with this a little and apparently you can cause the MODE PID to read "PT" with LESS THAN a 0.1-volt change in any APP PID and no change in percentage. Yes, the pedal is bad but man! Talk about splitting hairs.

Bruce Amacker · November 20, 2009

Wow, good info! Some IH's have a similar problem when the "up" stop on the pedal wears out from heavy city driving. If idle voltage falls below about .38v on an older IH, the ECM won't recognize the voltage, won't set DTCs and the throttle won't work. Cycle the key and all is fine.

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GregKneupper · November 21, 2009

I have replaced 3 failed pedals on 6.4's. Mine did not surge like yours did though, they just had high idle concerns. They would idle at about 2500 rpm. Pulled up on pedal and concern went away. Of course a new pedal fixed all of them. I submitted a gcr on it and the pedals were sent to engineering to investigate.

Aaron · November 21, 2009

My personal truck idles up and down real fast (about 100rpm) and the VGT actuator goes back and forth really fast when it's up on the cold idle warm up strategy, or up on the PTO, but only when it's warming up.

Not sure if this is the same concern you were having. I have no DTC's.

Wierd, and hotline says i should compare to like unit, suspect normal operation - I didn't spend an extra $8k to have it idle like shit when it's cold. From time to time it idles like it's got a really big cam in it when it's cold.

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