Loping/Surging At Low RPM/Acceleration

[Gomez0918]

Any luck with an answer on this?

I know it’s been a while.

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[Bud2723]

I'm having a similar issue—the 2018 G56 truck.

In 4th, 5th, and 6th gear, anything past 50% throttle is hesitant/ surges; the truck kind of shakes a bit just because a black market cat fuel filter conversion issue is still there.

Any ideas?

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[kgharrin]

You need to monitor actual & desired rail pressure and report back.

It could be your fuel control actuator (FCA) or some other fueling-related issue.

As others have suggested, your VGT actuator could be another thing to investigate.

Without details on the rail pressure and VGT position error, it will be difficult to give helpful advice.

Is it only happening during cold weather?

All conditions?

Warm/cold engine?

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[Corkey]

Unplugging the FCA on the CP3 will give you max rail pressure.

If you're not shimmed or plugged on the rail, you may pop a code, fuel pressure relief activated.

This indicates that you are above your threshold of which the rail is limited.

This only dumps the excess fuel back into the tank until the pressure is relieved.

Unplug FCA, start the truck "with no throttle," check the numbers for actual v desired, and shut the motor off.

I forget what the deviated number is between the two.

They should be relatively close to one another.

You will notice a sound different than usual, as this is giving you max rail pressure at idle.

If the numbers are pretty close, I will look at the VGT van position as stated above.

If those are in good standing, I'm curious if, depending on how many miles are on the CP3, it's going out or not.

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[Corkey]

Any new update on the numbers?

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