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Discussion Starter #1
IN the dealers recent attempt at grasping at straws to fix my truck, (read previous posts about the consistant low rail pressure code, the dealer put on a new fuel cap. (which by the way didnt work). When the dealer told me he was going to try this, he said it could possibly be it (which my response was , if its a fuel cap,then why does my truck only not work when its very cold, he couldnt give me an answer jsut a , lets try it and see), but got me to wondering if its totally vented or if its like a gas cap on a car there is supposed to be a valve if you will that when there is so much of a vacuum created (because you are using fuel and need something to replace the used fuel), the "valve" opens and allows air in. I was wondering if it is like that or if since its a diesel, its still a totally vented cap.
 

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Sealed.
 

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OK next ?, thanks for the quick response by the way, I will get flamed about this, but would it be a good idea to drill a few TINY TINY TINY TINY holes in the cap so you know that isnt the problem. I know theres a few cars I have seen that if the fuel cap is loose like that or lets in air all the time, it will set a check engine light will ours???? I know the main reason for going to sealed systems is for "enviromental reasons", but unlike gas, our diesel fuel doesnt really evaporate. I know my old 6.5 I had some problems with the fuel caps so I took a little tooth pick in the very center of the bottom, pushed that up (little piece of plastic and spring, and wedged a tooth pick in their no problems since. Can/ should I do that w/the duramax so I know thats letting air in and not the problem. I would try driving w/the fuel cap loose but w/these goofy motors dont know if thatd set a code or not.
 

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I have 203,000 miles on my 06 lbz with a sealed cap and no problems. Its not your issue, I wish I could give you a better answer. The only p0087 low fuel pressure code problems I have seen were caused by a bad fuel filter or gelled fuel. If it were me, I would try a different dealer. Heck leave the cap loose and drive it, that would be an easy way to eliminate the cap.
 

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Discussion Starter #5
Well they put the new cap on it already, but as I said I ask him hey whatever fixes it but if its the cap, why does my truck only do it when its cold not warm, he said lets try it. I dont think its my problem either, just didnt know if they were like some cars that dset ses if you leave the cap loose. I wish somone could give me an answer. Its had 2 new fuel filters on it and 4 different tanks of fuel w/plenty of anit gels. He told me some sensors were giving hme 600% readings when they should only go from 1-100% and wasnt sure why either. It only happens when its 0 or below. I even bought fuel at the same place we buy fuel from for the trucks at work with additives. We dont run any additives at work and trucks at work are ok. (I did buy it same time frame and day so I know I got the same fuel as in alot of our trucks). I almost want to try another dealer as I fee l they are jsut hunting and pecking and grsping at straws but I started w/them and dont know fi switching dealers in the middle of the problem would be a good idea esp since gm cust service is involved. Supposedly a block man or regional rep has looked at my truck too and they arent sure, doesnt make alot of since. Its something little and stupid like a kink in a fuel line whatever (which they supposedly checked)something little and stupid like that but they cant find it and this everyday to a dealer is bull. I know alot of guys running d maxes w/no problems. I just wish theyd get it worked out. Besides these recent problems, the truck is good.
 

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When I was having fuel problems along Interstate-90 I was not the only one. However, there were literally dozens of over the road trucks along the way that were having problems. After discussing the issues with several of them a common denominator came out. All of the guys I talked to were running newer model Cats with very small micron filters like what are on the new '06 D-Maxes. Older rigs weren't seeming to have an issue. If the other rigs you have at work are not using 2 micron or smaller filters they may run just fine when your D-Max does not.

I've said this in other threads, but I will repeat, I do not think that the current crop of additives are working worth a damn with some of the ULSD out there. I know for a FACT that they mad NO difference in my truck at all when I was having problems. The ONLY additive that did anything to clear up a clogged filter was Diesel 911. The only thing that kept the filters from re-clogging after I filled the tank again was finally making it to Montana where I could buy some good old fashioned #1 Diesel.

I really think your dealer is lacking in diesel experience. Changing a fuel filter is not that big of a deal and it is an instant test to see if you are having fuel problems. Change the filter and run the truck like Hell. If it runs good for over an hour, then sets a code again I can virtually guarantee that you are having a fuel issue with your supplier. If the problem goes away after it warms up, once again its a fuel supply issue.
 

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Discussion Starter #7
I tried diesel 911 didnt help. Also got chewed by the dealer because it has alochol in it, I knew big no no but they were so determined (at first) it was fuel. YOu can change the filter, instantly floor it unde rload(ie on a hill) and shes down again. I agree w/the dealer, poor design no lift pump, and another stupid problem (kinked line in tank whatever) is goofing me up. I do agree thought the stealer isnt experienced.
 

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Ok, then, it does look like they managed to find it was a flow problem of some sort. Have they pulled a sample of your fuel and tested it in any way? By reading your post I assume the truck has issues right after leaving a warm shop also?

Is there a sock/filter on the fuel pump at the tank? I have no clue on this one and would like to know myself. Fuel flow issues are not that technically complex, they just take time to hunt down the culprits.
 

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thejdman04;1599118; said:
OK next ?, thanks for the quick response by the way, I will get flamed about this, but would it be a good idea to drill a few TINY TINY TINY TINY holes in the cap so you know that isnt the problem. I know theres a few cars I have seen that if the fuel cap is loose like that or lets in air all the time, it will set a check engine light will ours???? I know the main reason for going to sealed systems is for "enviromental reasons", but unlike gas, our diesel fuel doesnt really evaporate. I know my old 6.5 I had some problems with the fuel caps so I took a little tooth pick in the very center of the bottom, pushed that up (little piece of plastic and spring, and wedged a tooth pick in their no problems since. Can/ should I do that w/the duramax so I know thats letting air in and not the problem. I would try driving w/the fuel cap loose but w/these goofy motors dont know if thatd set a code or not.
You can try leaving the cap loose. It will not set a CEL because our trucks don't have EVAP systems like gassers. I think your dealer is barking up the wrong tree however. Have they checked to see how much vacum is at the test port to determine if it is a clogged filter or a fuel starvation problem?
 

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Discussion Starter #10
AKDoug;1599384; said:
Ok, then, it does look like they managed to find it was a flow problem of some sort. Have they pulled a sample of your fuel and tested it in any way? By reading your post I assume the truck has issues right after leaving a warm shop also?

Is there a sock/filter on the fuel pump at the tank? I have no clue on this one and would like to know myself. Fuel flow issues are not that technically complex, they just take time to hunt down the culprits.
They puled a sample of fuel, does not have issues when leaving the warm shop either. Sometimes they will clear the code and send me out the door (in the shop less then 5 min), and no problems on the way home. There is supposedly no pump in the fuel tank. I know its not that complex its something very very stupid and small but they cant find it and Im fed up w/having problems on a new truck. I know every truck has quirks and has bugs, jsut life, but this is too many times for the same problem. Saturday, the truck when accleerating went like a bat out of hell up to 21-2200 rpms then just stayed there at that rpm even w/the pedal down (not all the way floored) then all the sudden picked up and revved way up to about 3000 rpm and took off. no check engine light. ran about 50 miles after taht fine. On the way home did it once too when I was almost home after the truck had ran quite awhile and it was 28 outside?????? They ahve put a vacuum guage on it also, they say thats fine.
 

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There was a post last summer of a member who fueled up and forgot to put his cap on and got better fuel mileage and did not set any codes. He stated 2-3 mile per gallon improvement. I also do not think it is the fuel cap. Maybe GM needs to invent a fuel warmer near the tank in the winter. Put it right next to the fuel cooler used for the summer! Or maybe a fuel cooler cover to prevent cooling the fuel. When the truck warms up, the fuel filter is right next to the motor, so I would assume that the motor would heat the fuel a little. In any event, keep plugging and keep us advised!

Good Luck!
 

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Diesel fuel cap does vent - but only inward to break vacuum. The service life on a factory cap is about 3 to 5 years - but I doubt that's your problem also.
 

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For your information , the cat engine never returned as much fuel as the other manufactures and that is why they have problems with fuel jelling .
 

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Discussion Starter #14
Didnt fix the problem same thing, will be calling dealer and gm cust service tomorrow:( othere then these problems, Its a good truck, sure is nice when it works.
 
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