Erratic Idle ICP Fluctuation - Ford Powerstroke Diesel Forum
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Old 07-24-2013, 04:33 AM
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Erratic Idle ICP Fluctuation

I just recently replaced the head gaskets and put in arp studs in my truck, heads were machined and pressure tested. It has about 85000 miles. Everything went great with the install. The truck is tuned with bolt safe looney tune I never retuned after the studs. When I first started driving the truck after the install I started getting an erratic idle when the truck is warm. When the truck first starts cold, it idles great smooth and feels like its hitting on every cylinder. Once warm the idle starts getting a little choppy and then it feels like its dropping a cylinder out. The cylinder wont stay dead, it comes and goes..

I have checked all push rods and hot or cold at any throttle there is no misfire, it runs great. Only when you drop back down to idle it will start running funny. I have a livewire and a scanguage. With the scanguage you can watch the icp and the ipr. After a cold start I can watch the ICP start to drop and when it gets around 600psi the cylinder or cylinders drop out, and you can visible watch the computer raise ICP and pull the cylinder back up to a normal idle and then from there on its a constant balance of icp drop off erratic idle then the pcm pull icp up and cylinder back in.

I do not have any codes and when the injectors were out I checked the spool valves and the were varnish free. There is no stiction at cold start. I have installed the blue spring kit as well.

I have replaced the standpipe, dummy plugs and stc previously before head studs due to a long hot start which took care of that issue. Also has fresh rotella t6 and motorcraft oil filter. Fuel filters were changed within the last 4000 miles

Any help appreciated. It seems oil related or oil side injector related. Also, this happens on stuck or tuned truck.

Last edited by reilly828282; 07-24-2013 at 04:37 AM.
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Old 07-24-2013, 01:43 PM
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This afternoon I got the opportunity to get my hands on a snap on motis I watched all parameters and watched for misfires and could not get anything to act up. I started killing cylinders and it felt exactly like what I am experiencing but could never get it to coincide with the misfire because it is so random.

I watched all parameters and they seemed normal. The only issue that seemed to have an effect was when I would raise ICP the misfire got worse. With the scanner I could raise it as high as I wanted and it would make the whole truck rattle. When I brought it back down closer to desired ICP it would idle fine. Any help or anymore direction would be appreciated. I watched all 8 cylinders for misfire and none showed up when watching while raising rpm.

I do know when the misfire occurs the pcm raises the ICP to get it out of the misfire "feeling" I have. When the pcm starts easing the ICP back down it will start misfiring again, and just seems like a cycle.

Thanks Reilly

Last edited by reilly828282; 07-24-2013 at 05:35 PM.
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Old 07-24-2013, 04:03 PM
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Thats becuse that is exactly what is happening, the pcm is adjusting rpm trying to compensate for another sensors readings that do not quite compute. You need to epand your pids you are watching and see what else is out of wack.

The pcm constantly adjusts things just normally you do not notice unless watching actul values. This time it's adjustment swings are large enough to be nticable.
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Old 07-24-2013, 04:31 PM
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RIELLY828282,
I seem to be having the same problem, my RPMS will fluctuate maybe 75 rpms have replace just about everything involved and its driving me crazy. It will be interesting what you find. I have a 96 F350 7.3 almost 270000 miles with a few mods
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Old 07-24-2013, 05:09 PM
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I understand it is doing what it is supposed to, although the confusing part is the ipr regulates all 8 injectors. But when I watch contribution on the motus no cylinders are less than the other. I know the motis isn't as advanced as the rest but still shows a positive and negative real time on all 8 cylinders. So what other pids do you suggest I watch? Icp ipr ebp maf what else? Thanks

My rpm doesn't actually fluctuate much.. Just feels like a dead cylinder. Off and on... I have checked the harness and didn't find anything and ficm all three voltages are steady.

Last edited by reilly828282; 07-24-2013 at 05:35 PM.
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Old 07-24-2013, 05:45 PM
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I would watch all of those and mebe ficm sync[both] crank and cam sensors [actual readings] (graph mode if possible). Pulse width also and rpm mebe even.

By the way if you see a fuel pressure pid ignor it, it is not for a 6.0. The 6.0 has no fuel pressure sensor, only a mechanical gauge will read fuel pressure on a 6.0

Also a snapon modus is not a flyby night scanner it just isn't really programed for diesels.
That said I hear the newer versions have a better code base for dieselsand more pids.
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Old 07-24-2013, 05:57 PM
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Right I just installed a blue spring and have a fuel psi pressure test kit to watch fuel pressure. So ficm sync I can check on my scanguage but crank and cam ill have to check with the motis. Should cam and crank be stable readings? Thanks
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Old 07-24-2013, 07:50 PM
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Cam crank should change with rpm increase but should be not be choppy or sporadic, values should change smotthly in relation tothrottle input.
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Old 07-25-2013, 08:01 AM
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Since this symptom only happens when warm at idle, I'm wondering if one of the orings inside an injector is bad. Like a small high pressure oil leak that is pushing oil and not delivering at low icps. The only thing is how would one figure out which injector? Pull the icp and air test and listen for the leak? Thanks
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Old 07-27-2013, 10:50 AM
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I am having the same issue, and it only happens when mine is warm. Funny thing is I recently had all the headwork done just like you. My miss continues up to 12-1300 rpm though.
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