2013 LML Duramax stalling at higher rpm

This is a 2013 GM 3500 with a LML duramax. The engine is a new build with egr delete, dpf delete. cp4 pump and all injectors are new including rail pressure sensor and fuel volume control valve on front of rail. all new gm parts no bs parts from other dealers. the truck will run beautifully until given any load, when driving if the rpms go over 2500 the vehicle acts as though the intake flap is closing, looses all power and will start to fuel knock. no smoke or data concerns that i can find. vehicles actual and desired rail pressure are spot on with each other and commanding 18 to 24k and actual matching when problem happens. even in park you can rev the vehicle up and hold it at 3k rpms or so and it will kill itself out and even stall. current tune in vehicle is a ez lynk 150hp, tried other tunes from same tuner to no resolution, also tried a hp tune and ezlynk from different writer and also a h&s to and all have the same effect. cam and crank sensors have been changed and relearned, fuel has been drained and filled with new, fuel filter and oil are all new as well as air filter. the truck will display the same issue with the intake flap held open and even with the vehicle run as naturally aspirated and the cac pipe at engine completely off. have sent data logs out to some people with no answers. looking for some advice on what i may be missing here or if someone can look at data files to see what i may be missing

Wild a** guess but have you logged the MAF to see if it is failing? I have had somewhat similar issues about 3 or 4 years ago when a customer had an Amazon MAF that was skewed and simply had bad numbers up high. Again wild guess on this but logging is free.

Unplugged mass air flow and it does the same thing but good thought. I have a log if you want to see it?

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Originally Posted by dfitz21

Unplugged mass air flow and it does the same thing but good thought. I have a log if you want to see it?

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Attachment 126996

Can't open it. Wants me to update my software. Nope. Sorry

Should I log it with an older version or a different software like efilive? Id be glad to pay to solve this issue.

Use an older version.

Here is the truck idling and then I hold the accelerator pedal at a steady 3k rpms. After 5 seconds the truck loses power. I keep the accelerator pedal steady the whole time. Then you can see it come back a little.

You are dropping fuel pressure. Here are the most likely issues.
1. CP4 taking a dump. Symptom is no smoke and no power
2. Fuel pressure sensor failing. usually get black then white smoke from over-fueling.
3. Vac leak in the supply system. Filter housing, hoses etc. Test is during symptom immediately shut engine off and seen how many pumps on the prime pump on the filter housing it takes to get a firm pump press. I will often use the GM clear line to look for bubbles. Can be cured with an aftermarket pump system.
Reason I see it is fuel pressure related is if in the beginning I have a snapshot of when it is running OK of 1,432 rpm, 11.09 lbs per min, and 9,851 psi rail. When it begins the symptom you have 1,405 rpm 16.05 lbs per min, and 10,045 psi. Graphing shows a higher reading than the proportional reading of rail pressure.

This is based off of a VERY limited information and NONE of my test equip hooked up. My suggestion is get it to a qualified Duramax daig tech for a good accurate diagnosis.

Ive never seen a failing CP4, only good or bad. I suppose I could try that. Fuel pressure sensor is new ac delco. No vacuum leak in fuel system.

Pressurized the fuel system to make sure the low side volume was correct and sufficient and no changes. Have new cp4 to install tomorrow and will report back. #themechanic which other test equipment would you have used so I can add them to my equipment?

My favorite is the Kent Moore Fuel pressure gauge. It has a Duramax fitting that snaps right on the service port at the front of the engine.
https://www.ebay.com/itm/22493843393...gaAnMCEALw_wcB
Attachment 127201

Love this tool. I bought mine full price :( Shows fuel system leakage as bubbles. Suction side.
https://www.ebay.com/itm/233249091316Attachment 127199

Have had many fuel filter brackets leak
Here is the diag that can be used for MANY years
Attachment 127200

Forgot to add. The Fuel pressure gauge works with all fuels and pressures including trans etc. Has several adapters and very accurate. The think I like about it most is the sensor is at the fitting and there is a LONG heavy duty wire that has a hard plastic protector over it and I can run it all the way inside the vehicle. Fantastic tool. Again I paid full price for it when we were getting them at the dealer but I don't regret the price. It has made me a hundred times the $800 I paid for it. Luckily they are now plentiful and MUCH cheaper including used.

Thanks #themechanic. I installed a new CP4 with no change. I bypassed the fuel tank, fuel filter bracket and fuel filter with 1/2" diesel fuel line and a fuel can. Still does that same thing. This must be a simple issue that I created when I reinstalled the engine. When it loses power it knocks like its running lean. I have unplugged both air mass meters and same issue. Is there something I could have plugged in wrong? What else would make it run lean/out of fuel?

Sorry took the weekend off. You need to check the scan data. Fuel in is power out as long as it isn't clouds of black smoke. Most common is going to be MAF skewed, bad fuel pressure sensor on the left rear of the motor, turbo failure, boost leak/lots of times it is a hole worn into the left side aluminum pipe wearing on the power steering/frame rail. Make sure you have good fuel Mpa under load. I like to run it real hard and the moment the you have low power shut it off immediately and coast to the side of the road. Then push on the prime at the fuel filter. Any more than about 5 full pumps without it firming up is a supply problem.

So the issue turned out the be pressure regulator in the diesel return line. The part was new but aftermarket and it was bleeding down. Installed a factory line and problem solved. It would not produce any check engine codes. Thank you again for the help.

No problem. That still should have shown up on data stream for fuel pressure mpa. I have an MDI2 and Techline Connect so one of the first things I do is command full fuel pressure at an idle to see if they system is capable of high pressure. It shows on the data stream and you can hear the audible change in the idle of fuel rattle.