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Thread: Surging At Idle

  1. Top Of Page | #1
    Mjhockey155's Avatar

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    Surging At Idle

    I started having some surging at startup when cold.

    So I’m thinking of some fueling issues.

    I have an MM3 and monitoring some rail pressure.

    See the image, for example.

    There’s actual, desired, and rail pressure rationality for the PIDs.

    What does rationality mean?

    Also, what does the FCS fuel Control State mean?

    Numbers go from usually 8 up to 96.

    I will do some data logs to see fluctuations between desired and actual. So I’ll report back on that. I don’t have any codes.

    The truck only has 60k, 2017 with exhaust and EGR upgrades”.

    It sounds a little more “ rattled” throughout all RPMs.

    I also notice at idle; the actual pressure seems to jump around and doesn’t stay constant.

    I know many things to consider, but right now, I am just trying to understand correct rail pressures and how to diagnose them.

    You can see on the monitor picture that the actual rail pressure hit 28,045. Seems too high?

    Also, notice so far that it is always lower than desired.







    2017 3500 CCLB DRW 4x4 3.73, Shocker Nightmare train horns, 5gallon on board air with Viar compressor and regulator, mag-hytec diff cover

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    Teflon's Avatar

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    Surging At Idle

    Any update?

    2016. Laramie 2500, 68RFE, CC 4x4. DRD Medical plan. factory rear air. 2” lift/level. 35x12.5, Revmax vb with deep pan. ARP 425 head studs.

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    Nito6two's Avatar

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    Surging At Idle

    My 2015 does it to.

    Pretty frustrating problem to chase.


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    Abgunnar's Avatar

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    Surging At Idle

    There is another thread talking about this.

    I don’t know how to post it.

    But it is most likely the grid heater pulling the voltage down, and you get the surging till the alternator can keep up.

    I’ve done some testing, and if you disconnect the positive wire to the grid heater relay and start the truck, the surging goes away.

    I have tested it several times, and it works every time.

    Watch your voltage; when you start it in the cold, you’ll see it drop to 11.4 when the grid heater is on, and as soon as the voltage goes up, the surging will stop.

    2014 2500 on Fuel rims, custom aluminum grill emblem, mm3 DRD tuned, 4” jamo tbe exhaust, led fog lights, steering box brace, took Vinyl off doors.

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  9. Top Of Page | #5

    Surging At Idle

    Not sure if you found the issue, but I had a similar problem and replaced the fuel pressure relief plug with a solid one.


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