[Jlaymance]

2015 Gmc 2500hd Denali
Fully deleted
Straight pipe
Ez link 5 switch tuner
H&S turbo top pipe
Airdog 150
Cold air intake.
187k miles

Problem started 11 months ago after a wreck and had to put a brand new frame on the truck. Truck was fine for roughly 3 months after frame swap. Then randomly the truck hesitated as if it was running out of fuel. So I changed the fuel filter. Problem was really random after that. Sometimes truck would drive fine under any conditions. Then the truck would start to hesitate (feels like running out of fuel/ fuel knock) after 70 to 80 miles. Once the problem would start for the day it would get more noticeable as the day went on and miles were driven. Thought myb a bad filter so swapped it out and problem is still there. So then thought myb the filter housing needed to be rebuilt myb a air leak. Got a kit and problem still existed. Talked with a mechanic he said rebuild kits suck to buy new oem filter housing same problem new housing wasn't the problem.

Truck spent 35 days at GM dealership they said the truck is fine and they could not get truck to act up at all. So I picked it up and 80 miles later problem shows up again. Zero codes and no check engine light comes on.


So I took it to a local diesel only truck repair shop with a great reputation in Texas. They said in testing 2 injectors were way low around -4.6 and -4.8 and two injectors were at +4.6 and +4.8

So they recommend to replace all 8 injectors so I had them put in all new stock injectors and a fuel pressure regulator with the upgraded screen that is supposed to help save fuel system in event of cp4 failure. They said truck is good to go. So I picked up the truck and noticed immediately the power is way less then normal all all 5 tunes. So I drove it about 80 miles and the hesitation problem didn't show up at all. However 45 min later I drove the truck 1 mile and let truck idle for 15 min and when driving 1 mile back home truck hesitated again same as before. So I thought myb a air bubble so I drove it for 1 week and hesitation problem wasn't a issue, however definitely a loss of power.

Then one afternoon problem stared and didn't go away at all. Next day no miles driven at all and problem shows up again and is constant now.


So I took it back to the shop and they checked injectors and they all check out cp4 is putting out 28k to 29k psi under load. Turbo is producing 28 to 30ishs psi under load. Fuel system checks out turbo checks out but problem is still there.

So the shop has even replaced ecu now and reloaded factory tune and ez link tune. The problem still exists. The problem is only around 1750 rpm to 2250 rpm once the truck shifts the problem goes away till the 1750 to 2250 rpm range till transmission shifts again. The only way to describe the problem is temporary running out of fuel/fuel knock but the truck never dies or goes into limp mode and never shoots a code.

The guys at the shop are pretty stumped as well they don't know what's going on with the truck because via computer the truck is right with no issues at all but there is a very real drive ability issue between 1750 rpm and 2250 rpm.......any ideas guys everyone is stumped on this one.



I just need my truck back asap any help is greatly appreciated Guys!

 

[Branden c.]

Maybe the mass airflow starting to act up.

 

[ATCinfantry]

HPtuners with a scanner is what you need. Data log all the parameters for the truck and itll show up. I know its more money but that scanner logs so much that its easy to find it. Know any local tuners in the area that would hook up to the truck and log it?

 

[Jlaymance]

We replaced that as well I forgot to put that in the post. I will say during working on the truck at a buddies house we had mass airflow unplugged and I had to go to my house and grab a couple tools. The hesitation problem was more apparent and obvious. When I got back I noticed it was unplugged. So I thought it was going bad.So I replaced it the next day and problem still existed. I would assume ecu would kick a code for mass air flow was bad. That's the bad part as far as the ecu is concerned all is well under the hood

 

[Jlaymance]

HPtuners with a scanner is what you need. Data log all the parameters for the truck and itll show up. I know its more money but that scanner logs so much that its easy to find it. Know any local tuners in the area that would hook up to the truck and log it?

It's at a shop with Snap on computers and also same computer as dealerships. They have done multiple data logs with nothing showing up as a issue. Is HP tuner different then snap on and factory GM computers?

 

[2019LTZ2500]

It's at a shop with Snap on computers and also same computer as dealerships. They have done multiple data logs with nothing showing up as a issue. Is HP tuner different then snap on and factory GM computers?

ATCInfantry's suggestion of using HPtuners with a scanner is a good one. I found in unmatched back when I used it on my gas hotrods. Its much more capable then anything snap on has for capturing data, and as far as the GM stuff is concerned its only as good as the people that operate it and the time they put into it. I don't know about the newer GM MDI-3 but forget the older Tech 2, HPtuner has it beat too. Personally, I would suspect the FPR especially considering your description of how it acts up during a shift. The only other thing that comes to mind is the CP4 is getting up there in mileage, has anyone checked the screen? It might give you some hints what is going on as well.

 

[Jlaymance]

ATCInfantry's suggestion of using HPtuners with a scanner is a good one. I found in unmatched back when I used it on my gas hotrods. Its much more capable then anything snap on has for capturing data, and as far as the GM stuff is concerned its only as good as the people that operate it and the time they put into it. I don't know about the newer GM MDI-3 but forget the older Tech 2, HPtuner has it beat too. Personally, I would suspect the FPR especially considering your description of how it acts up during a shift. The only other thing that comes to mind is the CP4 is getting up there in mileage, has anyone checked the screen? It might give you some hints what is going on as well.

Yes they checked screen and no sign of any metal. I will look for someone with HP tuner.

 

[Nate Dmax]

I would agree that an extensive data log comparison is needed. Even down to what the transmission is doing. Don’t focus everything on the engine as transmission communication could also come into play. Just a thought.