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06 GMC Sierra 2500hd 4WD LBZ stock, lift pump, 147k miles.

Long post but please bare with me. So there is a strange thing that happens with my truck ever since I got back from a boat trip. The truck had been sitting for about 3 months in my garage and since I’ve started to drive it again, at about 140 degrees coolant temp, fuel pressure drops and truck bogs. Throttle response is little to none and when you go pedal to the floor the truck jerks until you let off. This issue goes on until 144 degrres coolant temp. I usually have to pull over and come to a stop for it to go back to normal. The truck is not starving for fuel, desired and actual are spot on, its the desired*** fuel pressure that drops. Also it usually seems to happen in 5th gear unlocked. NO CODES. I’ve replaced my fuel filter and have done a decent look over on the truck but it does not seem like a mechanical issue. Anyone have some input on this? I’m stumped and its getting kinda dangerous especially when you have no power going 40-50 mph. Thanks
 

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This is one of those things that could be a lot of different things. Have you checked your fuel filter housing for air leaks? I had to rebuild mine right around the same mileage. My symptoms were a bit different though, in that the fuel system would loose prime when sitting. The truck bogging when it reaches 140 could be a red herring (coincidence). Can you replicate the issue with the truck sitting in your driveway (get it up to temp, what does it do)? Also, you mention the desired and actual fuel pressure are spot on, but then later say it's the desired pressure that drops. Can you explain?
 

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I think you need to get a good scanner and data log it to be honest, that's super interesting.
 

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This is one of those things that could be a lot of different things. Have you checked your fuel filter housing for air leaks? I had to rebuild mine right around the same mileage. My symptoms were a bit different though, in that the fuel system would loose prime when sitting. The truck bogging when it reaches 140 could be a red herring (coincidence). Can you replicate the issue with the truck sitting in your driveway (get it up to temp, what does it do)? Also, you mention the desired and actual fuel pressure are spot on, but then later say it's the desired pressure that drops. Can you explain?
I forgot to mention i have a lift pump that bolts in place of fuel filter housing. No leaks that i’ve seen. And when i mean the desired and actual are spot on, i mean they match eachother but they are lower than they should be. Tops off around 8-10k psi and then around 140 degrees coolant temp it’ll drive like nothing ever happened.
 

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What do they top off at when you get up to operating temperature?
 

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If the fuel pressure isn't where it should be, I'd think a fuel delivery issue. If you replaced your stock fuel filter, what are you doing for water separation? Tried bypassing your lift pump? Is your lift pump free flowing if it fails?
 

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at about 140 degrees coolant temp, fuel pressure drops and truck bogs..... The truck is not starving for fuel, desired and actual are spot on, its the desired*** fuel pressure that drops.
....
So where does the desired fuel pressure come from? ECM. Unless the ECM is getting some information that something has changed, or a circuit problem from some sensor, don't be surprised if the problem is your ECM. For engine coolant temps, LMM's have 2 ECT sensors, one for the gauge, one for the ECM. Make sure both are working correctly. And what receives the dropped signal from the ECM? FPR (fuel pressure regulator mounted on the fuel pump). So there could be a problem with the FPR not correctly responding to the change in demand.

This is not to tell you where the problem is but to let you know more of the complete picture and to make sure you understand that your engine is interconnected to many moving (electronically speaking) parts and you have to make sure all the parts are doing the correct signaling at the correct time, and temperature, in your case.
 

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I do not like throwing parts at a truck, but I would not be surprised if it is an ECT or something on that REF circuit.
 

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....
So where does the desired fuel pressure come from? ECM. Unless the ECM is getting some information that something has changed, or a circuit problem from some sensor, don't be surprised if the problem is your ECM. For engine coolant temps, LMM's have 2 ECT sensors, one for the gauge, one for the ECM. Make sure both are working correctly. And what receives the dropped signal from the ECM? FPR (fuel pressure regulator mounted on the fuel pump). So there could be a problem with the FPR not correctly responding to the change in demand.

This is not to tell you where the problem is but to let you know more of the complete picture and to make sure you understand that your engine is interconnected to many moving (electronically speaking) parts and you have to make sure all the parts are doing the correct signaling at the correct time, and temperature, in your case.
Ron, I know where the ECT sensor is for the gauge, where is the ECT Sensor for the ECM located?
 
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