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Discussion Starter #1
This is a long post sorry...

2007 gmc duramax
Pulled a 44ft enclosed race car trailer that weighs about 16k a lot.
Truck pulled trailer about 80% of its miles.
Truck was hardly ever empty
Truck was factory stock
Only thing we did to truck at first was put 100 gallon tank in bed. Had a in-line filter in between it and stock tank. We only put fuel in big tank so it was filtered before getting to stock tank.
Truck also has had since new a aftermarket locking fuel cap.

Truck ran fine till about 2011.
1st time it went into â reduced power was pulling the trailer at about 75mph down interstate. On flat ground. Had been on the road for a little over an hour. It would only go 20-30 in reduced power. Pulled over shut off for a few minutes. Still wouldn't reset. Had to disconnect both batteries for a few seconds to reset. We still had another hour to destination. It would go into reduced power every half hour or so Even though we started driving it easier. We changed fuel filter. Everyone always jumps to fuel filter. In my experience it is almost never the filter. Truck had about 100,000 miles when it first started trouble.

Took truck to 1st place. A dealership in silver city. Same place we bought truck. They said nothing wrong with truck.

Took truck to 2nd place a local diesel mechanic. He said exhaust filter was the problem. So we had him delete filter and put bully dog in and put bigger exhaust on and put in line fuel pump with 2 extra filters. So this is a total of 4 filters at this point. Truck is still having same problem.

Took truck to 3rd place a dealership In deming New Mexico. FYI. Don't go to this dealership. They have screwed me over repeatedly. They changed a couple injectors. Didn't help issue.

Still putting on 1,000+ miles a week on truck. Still Having to disconnect batteries randomly. Sometimes it will go an hour. Sometimes only 10 minutes. Rarely it will go 2 hours. It only has the problem pulling heavy trailers.

Took truck to 4th place. Dealership in El Paso. I figured a huge dealership might have a sharp mechanic that might help us. We even took a trailer so we could take mechanic on test drive after. Mechanic wouldn't test. They replaced a couple glow plugs. Said truck was fine.

Took truck back to deming dealership. They replaced 1 injector. They also said it needed a fuel line by the engine that is prone to getting crushed. We told them no. Didn't want to spend more money for nothing.

It is about 2013 at this point. I had to trade in my new camaro on a 2012 power stroke. So I could have a new tow vehicle. At this point I'm only pulling small trailers or using the dmax for a grocery getter at this point.

In 2015 took dmax to 5th place. It had check engine took to Dealership in Safford Az. They can't find anything wrong other than a couple injectors.

2017 transfer case goes out.

2019 we start to use dmax to pull small and medium trailers more. It goes into reduced power mode even more now.

For the first time it goes into reduced power going down hill.

For the first time i can shut engine off to reset. Or sometimes I have to just let off gas to reset. Donât have to disconnect batteries anymore

Took truck to 6th place. Local mechanic. He says without looking at truck that it is fuel line by engine passenger side.
Same thing deming dealership said.
He looks at it and shows me the fuel linesare weak and collapsing in.
He also says the primer pump needs rebuilt.
R103 fuel lines.
Cat conversion kit for fuel filter to handle extra pressure.
He replaces these.
No change. Still same problems

Year 2020 drive empty trailer to Loweâs 2 hours away. Shut off truck for 45 minutes. Load 10k on trailer. Drive 200 feet at 10 mph. Start slowing down for stop sign. It goes into reduced power mode.

July 2020. Mechanic #6 changes thermostats. Truck had been getting up to 160 temperature only for a few years. Now it stays at 210

Truck Pull empty trailer 2 hours to get 10k again. With trailer. Total is 14k.
Load trailer get on road for 1.5 hours. No problems thus far. Stuck behind car going 60 in 65. Start to pass. And it goes into limp mode. For the first time in a couple years I have to disconnect batteries.
It goes another 30 minutes and I stop for fuel. Get back on road for 5 minutes. It goes into limp mode going 50 mph. Half throttle.

Most of the time. It goes into limp at 1/4 to 1/2 throttle.

Yesterday. Mechanic #7
In-house mechanic says it could be tranny computer.

Today. Mechanic 6 says Might be Fuel pressure regulator. Get Oem only. Also says might be because we are running at full power tune.
 

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Sounds like you’ve had your share of incompetent mechanics.

Sounds like your fuel pressure relief valve. They tend to get weaker and weaker with time, pretty much exactly what you’re describing. The relief valve is popping, and you’re losing rail pressure and that makes it go into limp mode. You can either install a new one, or install a race plug, and never have to worry about it again.

The other possibility is a weak CP3, but I kind of doubt it. Didn’t catch what the total miles on the truck are right now?

Do you have any way to watch your desired and actual fuel rail pressure?


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I have nothing mechanically to offer but the fact that you have dealt with this for 9 years amazes me I applaud your patience.
 

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Discussion Starter #4
I dont have a way to watch it unfortunately, and the miles are the truck are 170k

Where would I find this race plug
 

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I dont have a way to watch it unfortunately, and the miles are the truck are 170k

Where would I find this race plug
Google “PPE race valve”. Available from numerous different vendors.

If you’ve got a bit of time you can do the “bottle test” to confirm the relief valve is bad.


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