02 Dodge Ram 2500 w/ 24 Valve Cummins VP-44

Hi all, this is my first time using this forum but I am at the end of my rope with my pickup truck. The Cummins runs great when cold but once she heats up the idle gets to be extremely choppy and erratic. She runs strong under a load and never misses once you get up off idle. I was finally able to put a current probe on my U-Scope and monitor the VP-44’s metering solenoid while it was acting up. Unfortunately I was unable to capture a shot of the current dropping out but the video clearly shows the waveform dropping out sporadically. Any thoughts? I’m skeptical of a problem with the metering solenoid itself and more concerned with the control side of the issue but I’m just not sure! Any help would be much appreciated! Please see attached videos.

There are no videos attached.

Hey PK! Sorry, but your videos didn't make it into the post. Let me know if I can help with that.

The metering solenoid (or Fuel Control Actuator, I think) on those pumps is normally open, meaning that with no current flow through the solenoid, that the pump defaults to max pressure. i.e. disconnect the solenoid, and the pump goes to it's highest output. The dropouts in current that you're seeing could certainly be a solenoid/wiring issue, but it could also be the PCM struggling to get the fuel pressure it's looking for, and turning the solenoid off to get it.

Do you have access to scan data? I'd be interested in looking at the fuel rail pressure actual and fuel rail pressure desired during the erratic idle. If it seems like the actual is 'chasing' the desired (they almost never agree), then definitely look closer at the FCA or low side fuel pressure. I've seen this symptom show up with a sticking FCA, causing idle and starting problems.

Hey Tyler and Pole71 thanks for getting back to me. I’m sorry I can’t seem to get the videos to attach from my phone. I’ll try on my computer and see if that makes a difference!

Ok so I was unable to get the videos but I do have photos of the waveform acting properly and then a shot of the Peak and Hold when the "Hold" seems to disappear! Tyler I hear what you're saying about desired not matching actual pressure but this is not a common rail system. The VP-44 is an actual injection pump that meters fuel as well as controls timing. There are two solenoids on the injection pump (Metering and timing) and they are controlled by the FPCM (Fuel Pump Control Module) which is mounted directly on top of the injection pump. I clamped a low amp probe around one of the wires coming out of the module and going to the metering solenoid and the pictures revealed that a peak and hold type circuit was being used. As I mentioned earlier the truck skips very erractically with no real rhyme or reason only when at idle. I found that the solenoid does still seem to get its initial spike of current (Albeit the spike is not quite as high, but a spike nonetheless) but the "hold" portion is clipped right off, cutting the injection event short and I believe therefore causing the misfire. I am just concerned with why the "hold" portion of the waveform is missing. I assume it to be a decision being made by the FPCM but why so sporadic??? and why only at idle? Am I dealing with a mis-reporting input signal causing a sporadic output control? Or could it be a problem with the solenoid and wiring? I shy away from a problem with the wiring or solenoid only because I have an acquaintance that had a very similar problem yet he threw a brand new built pump at the problem and it continued to display the same symptoms!!! Needless to say I don't want to make his mistake and throw a bunch of money at it for no solution. Thanks again for any input! Two of the photos are more zoomed in, but there are two pairs of "good" and "Bad" waveforms.
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