Loss of high pressure fuel pressure when truck gets to 180 and up

[DarrenKling]

04 5.9 C engine code 305hp engine, truck has plenty of power till truck reaches 180 thats where high pressure fuel will no meet fuel setpoint, example setpoint is 12k only has 5-6k on pressure. Now list on everything done and test done, truck came in like this tested lift pump pressure only at 3 psi at idle....lift pump had already been moved to the tank, so replace with a FASS 95 gph w/drawstraw, also found injectors with excessive return rates so replaced with NEW Bosch injectors and Bosch transfer tubes....tubes have been torqued proper, still have issue! I have a new cascade overflow valve to test with, no change. Installed a dummy "race valve" in place of pressure relief no change there. Install a new FCA/Mprop valve (fuel pressure regulator) no change. Then off of a running truck with no issues i switch fuel injection pumps with no change either! Tried unplugging coolant temp sensor to fool computer on coolant temp with no change also! Unplug FCA at idle goes to full fuel 20-23k but when at 180 and fuel pressure dropped it doesnt make a difference to unplug FCA. Did a lift pump volume test to verify spec per mitchell 1 is 590ml for 10 sec, well over at 835ml. Did injector return test after new injectors at operating temp spec is 180ml max come in well below max at 125ml for 10 sec test. done everything under the sun and might of forgot others i done, my back is against the wall and dont know what else to do,any help out there?

 

[cerberusiam]

What parameters did you use for the injector return test? The latest spec is 180-220 ml in 30 seconds at 21k psi and 1200 rpms, over 240 ml the injectors are considered bad. The 125 ml for 10 seconds does not bode well for, if that is what you are saying. Just checking as that is the only obvious thing that jumps out considering the symptoms.

 

[wildbill]

Is the truck completely stock? If so, try another rail pressure sensor. If it has a programmer, see if the defuel setting was messed with.

 

[DarrenKling]

Bone stock truck no programer

 

[DarrenKling]

Sorry i got my spec off im getting 100ml for 1 minute of idle on injector return

 

[AH64ID]

Have you tried a rail pressure sensor?

 

[wildbill]

Any codes? Also when you say loses power, do you mean it'll only let you get up to a certain speed, like it went into limp mode?

 

[AH64ID]

If it's happening with the FCA unplugged on multiple CP3s either the sensor is bad, there is a blockage, or a major leak likely in the head that opens when warm.

 

[sag2]

Except a leak in the head would show up in the return test. One other question, has the return test been done at full operating temperature? If not you need to do it. Also run the test with FCA unplugged and see if there is a significant difference.

 

[DarrenKling]

Yes test was done while at operating temp

 

[DarrenKling]

Also reply for FCA it will go to full fuel as long as its below operating temp, as soon as its reached operating temp and you unplug it, doesnt make a difference, fuel pressure will not rise

 

[cerberusiam]

Sorry i got my spec off im getting 100ml for 1 minute of idle on injector return

That sounds way low. IIRC, that should be around 1 oz per injector for a minute which is roughly 180 ml. You should do the latest test and see what it comes in at, it is more accurate.

 

[DarrenKling]

when the truck is cooler and running just fine and fuel pressure is fine i get the same return rate as when im having fuel pressure problems

 

[BLNRAY]

if you can find someone with access to cummins quickserve you can see all the ecm readings ,you can see the ecm commanded fuel pressure and the achieved fuel pressure.the 2 readings should be within 200-300lbs of each other.could be the ecm is bad and cutting the pressure.

 

[TCDiesel]

DarrenKing 3 possibilities ,You will need to call us on this.

 

[AH64ID]

Did you get it figured out?