I have just put a lot of work and money into my 2008 6.4 power stroke. (155k miles). NOW, the engine has a intermittent skip every 20-30 seconds when the AC is turned on. AND IT BOTHERS THE #### OUTTA ME.
My diesel tech has ran a contribution test and it doesn't show any injectors dropping out. It just shows a wave displaying across the screen across all when it "Skips". A compression test was done also and passed. My fuel pressure is showing 5,500psi at idle. NO codes are shown. The truck runs great once your on the road.
Why would the AC cause this somewhat power imbalance and engine idle skip with the AC on? Anyone else experience this?
Recent mods in the past 2 months:
1. New fan clutch
2. Whole new AC system.
3. New Up-pipes. And CAC Pipes.
4. New exhaust header manifolds. 4" turbo downpipe.
5. NEW FORD PCM.
6. Replaced the old H&S tune with new SCT GTX monitor.
Truck is already has full EGR delete. Straight pipe exhaust and cold air intake. with the new SCT tunes.
Could the diode be an potential issue even if the brand new ac system works perfectly fine? Could a failed diode cause the engine idle to skip? Like i said, the contribution test just displays a odd "wave" no complete drop outs.
When the ac coil de energizes, that stored energy has to go somewhere. Most vehicles have one installed from the factory in the fuse block or inline with the coil power supply. The diode prevents that energy from backfeeding back to the PCM or causing interference with the CKP (right next to ac compressor)or CPS sensors. A glitch in one of those sensor readings can cause a stumble. And voltage back feeding on circuits it shouldn’t can also cause this type of problem.
FWIW that odd wave you see is likely a disruption in the CKP sensor signal, or a result of voltage backfeeding the the PCM when the coil de enegergizes.
Is your mechanic using the IDS and VCM II for his testing?
This diode will likely have zero effect on the function of the compressor even if it’s bad.
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