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I have an 01 6.6 duramax with 175k miles. I am having what i believe to be a fuel issue. It idles perfect and starts right up every time. Normal driving is fine, holds good rail pressure and drives great. The problem is when i give it heavy acceleration. The truck stumbles. Hesitates if you will, like its not getting enough fuel. The rail pressure drops big time at WOT and the fuel pressure guage bounces like crazy. From 10 to 4. The guage flexuates a little at idle but not bad. Bounces between 10 and 11. I have an airdog hp150 on it. New injectors with about 30,000 miles on them. New fuel filters with less than 300 miles on them. New Air filter and MAS. I do have an EFI live 5 position tune on it. Ive also taken out the spring and ball on the return line on the airdog. I cleaned it and put it back. Seemed to help for about 30 miles then back to what it was doing. Also idk if this has anything to do with this but i think it smokes a little excessively. No white smoke, no haze at idle. Ive taken my truck to 2 different diesel mechanics and neither of them can figure it out. Im literally at a loss for words lol
 

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Welcome to DieselPlace
Do you still have the OEM filter head? Have you rebuilt or replaced it lately? If not, you may be sucking air past the orings in the filter head
 

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Discussion Starter #3
Welcome to DieselPlace
Do you still have the OEM filter head? Have you rebuilt or replaced it lately? If not, you may be sucking air past the orings in the filter head
No I have the airdog mounted by the fuel tank. The old oem filter housing has been removed. Ive checked the o rings on the fuel filters and they are good. The filters are sitting well and I believe them to be sealed well. Ive replaced them twice in the past 1000 miles just to make sure. Primed perfectly and all.
 

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How about all the sections of rubber fuel line from the old filter head to the pump? There are 6 or 7 sections on the low pressure side lines that could be cracked and causing trouble.
 

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I've checked everything I could see by eye. Everything looks pretty good. Ill start taking a few things off and take a deeper look at the hoses. I was worried about the lines collapsing but the mechanics I brought it to said the lines were fine.
 

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Off the FICM there are 4 or 5 segments buried in the V of the engine that you can't really see until you take things apart. I have them on the shelf and still have to change mine out, but the 2 for the filter head were pretty cracked when I did them last summer.
 

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Discussion Starter #7
Ok. Thank you. Ill do that and get back with you.
 

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Discussion Starter #9
They said they look new and fine lol but I have 3. One on the airdog pump, one on the cp3 and one down in the V on the block by the turbo. They are 220 each. I don't want to have to replace all of them and it still not correct the problem. Im starting to think it has to be one of those fuel regulators tho. All my lines look good.
 

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Discussion Starter #10
I believe I've figured it out. I checked all the hoses and they were good. Then I checked all three fpr's. (I unplugged them one by one and started the truck each time. Each time the truck would lope real hard. So that told me they were working when plugged in. So then I thought maybe my cp3 was going out or has "weakened" so I took off the return line and looked down in there and it was pretty clean. Everything I've read online says if its clean more than likely its not the cp3 going out or causing my issue. So then that brought me to check the fuel pressure relief valve. My thought was its been opened and weakened so I took it out, opened it up, stretched the spring and added a washer as a spacer. Put it all back together and boom problem fixed. I havent hooked it up and watched the rail pressure yet but I will. (Doing it this way I have no idea at what psi it will open up) The airdog psi guage still flexuates but not much. Bounces between 9 and 11 while driving. WOT drops it to about 6. Much better than 3.
 

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How about an update? Did the fprv solve your issues completely? Did it throw any codes? I’m having almost the exact same problem and can’t figure it out.
 

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How about an update? Did the fprv solve your issues completely? Did it throw any codes? I’m having almost the exact same problem and can’t figure it out.
Yes it completely fixed the issue. Shes running like a beast again. No codes were thrown.[/QUOTE]
 

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Awesome. Thank you.
 
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