Help - Trucks Fuel Rail Pressure Drops! - 2015 6.7L Cummins

[JosiasMorales97]

Hello, everyone, I have a 2015 6.7L Cummins, and I’ve noticed it has a lope or drop when it idles.

Like fuel is not getting fed continuously.

Well, I ran it on the highway yesterday, and suddenly when I was above 75mph, my truck started sputtering.

Fuel rail pressure would drop from 22 to 14-10 and jump back up.

This was all very quick.

I’d let off the throttle and speed back up. It would struggle around, then all of a sudden, it would surge and speed typically.

I don’t know if my lift pump is going out, my FCA, or maybe my tunes.

Which I didn’t get them from a reputable tune writer.

Mind you; I didn’t know any better. I change fuel filters religiously along with my oil.

They are never dirty, and I’m running Docs fuel filters.

The fuel system in the truck is all stock and has 185k miles.

Any help is much appreciated!!

I’m deciding between an Airdog or FASS fuel system and want to run CAT filters.

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[AK Bob]

Hello, everyone, I have a 2015 6.7L Cummins, and I’ve noticed it has a lope or drop when it idles.

Like fuel is not getting fed continuously.

Well, I ran it on the highway yesterday, and suddenly when I was above 75mph, my truck started sputtering.

Fuel rail pressure would drop from 22 to 14-10 and jump back up.

This was all very quick.

I’d let off the throttle and speed back up. It would struggle around, then all of a sudden, it would surge and speed typically.

I don’t know if my lift pump is going out, my FCA, or maybe my tunes.

Which I didn’t get them from a reputable tune writer.

Mind you; I didn’t know any better. I change fuel filters religiously along with my oil.

They are never dirty, and I’m running Docs fuel filters.

The fuel system in the truck is all stock and has 185k miles.

Any help is much appreciated!!

I’m deciding between an Airdog or FASS fuel system and want to run CAT filters.

It sounds like your FCA may be the issue.

You could check the flow rate on the lift pump.

If you choose a different system, I recommend FASS over Airdog and a NanoNet filter like the Fleet Guard FF5814 over the CAT IR-0750.

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[JosiasMorales97]

Thank you, Bob!

How would I go about checking the flow rate on the lift pump?

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[AK Bob]

Thank you, Bob!

How would I go about checking the flow rate on the lift pump?

Unhook the quick disconnect on the fuel supply line at the CP3 pump.

Measure the amount of fuel in a container.

Should gather between 400-600 mL (13.5 -20 oz) after 10 seconds on a good pump.


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[JosiasMorales97]

So I changed out the FCA, “was convinced that was the problem,” turns out it ain’t.

The truck is still doing the same thing.

It feels like it’s worse now.

It surges the idle when just sitting—low power when I try to accelerate.

Any comments/advice is much appreciated.

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[Corkey]

Check the actual vs. desired on the actuator for the turbo.

You shouldn't be surging at idle.

Also, check the max pressure on the CP3 by unhooking the single wire off the pump, get the rail pressure P.I.D on the monitor, start the truck, and see what the max pressure is reading.

Don't hit the peddle, as this is maxing the pump out at idle.

Just because the FCA is replaced doesn't mean the pump is good.

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