Calling all cummins experts

webb06

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2015 6.7 cummins
62,000 miles

Truck came in with low rail pressure and would barely move under its own power. Rail pressure was 3500ish psi. Any kind of throttle input and rail pressure would drop below 1000 psi and truck would stumble and barely stay running.

Checked fuel filters and there was a terrible amount of water in them. Changed both filters and removed the tank and cleaned it out. No metal in rail or lines. No change in the way the truck runs.

Replaced FCA. Now as soon as truck is started rail pressure ramps up over 28,000 psi. Tried another FCA off of a running truck. No change.

Sometimes the rail pressure will drop below 12,000 psi kind of like the ecm is trying to protect the system. Commanded pressure when rail is extremely high is around 9000 psi. When rail pressure is 12,000 psi commanded rail 22,000 psi.

Swapped a different cp3 onto the truck. No change. Removed injectors and had them tested. All tested okay. Checked low pressure supply. 10-12 psi. Unhooked returns individually, no change. Fuel rail relief valve only opens when FCA is unplugged.

Only code that comes up is P0088 high rail pressure. Checked voltage coming to FCA connector. 3.5v unplugged with key on. Compared to another truck and it is the same voltage. Replaced FCA connector because I saw many cases online of it fixing similar issues.

Any help or input is appreciated. Hoping to swap ecm with another truck soon. That’s about the only thing I haven’t tried I feel like.


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Black250

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What mods have been done to the truck? What's it's history? Flood truck? Sounds like something electronic is shorted or corrupted.
 

dmd

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Purely mechanical thinking it appears that there could be a restriction in the high pressure fuel line. Not sure if that is even possible with theses. Lets enough fuel through for pressure at idle but is too restrictive for any more fuel to get through and the pressure beyond the restriction drops when more fuel demand is need.
 

webb06

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What mods have been done to the truck? What's it's history? Flood truck? Sounds like something electronic is shorted or corrupted.



Been ******d since 1500 miles. Buddy of mines truck. Nothing crazy has happened.


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webb06

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Purely mechanical thinking it appears that there could be a restriction in the high pressure fuel line. Not sure if that is even possible with theses. Lets enough fuel through for pressure at idle but is too restrictive for any more fuel to get through and the pressure beyond the restriction drops when more fuel demand is need.



Don’t think any of the lines could be restricted. Literally happened in one night like flipping a switch. Truck idles fine. Even runs down the road fine. When returning to idle rail pressure is way to high.


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webb06

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Final update: customer did not have the efi autocal from when the truck was originally tuned so we had a local shop come down and load a stock ecm file into the truck. Rail pressure was perfect. We contacted the original tuner of the truck and they sent over the emission off file and reloaded it. Truck runs perfect.

No idea how or why the tuning got corrupted but I’m glad to see this one go.


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