Duramax Losing Prime!!!
 

Hey guys, I know this is a fairly common problem, but what the heck gives???
I just changed my fuel filter, no leaks anywhere, had the whole fuel system inspected 3000miles ago and they said it was perfectly fine, didn't throw any codes. I just picked up a Bully Dog tuner from GRI that I haven't had a chance to try yet, so I'll check for codes when I can, but does anyone know WHY they lose their prime? Where are potential problem areas? After pumping the fuel pump a couple times, it fires right up...
I let it sit for 4 days and it wouldn't start, had no pressure, I had to pump the manual pump until it was firm for it to start. Could it just be a cold weather fuel issue?


Thanks for any tips:humm:

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hmm... I'm thinking - it's not tight enough or I didn't tighten the bleeder screw enough, or it's the crap fuel that's in my tank right now or a combo of both....:argh: Maybe something came loose after I installed the new filter..

the filter and the bleed screw should be hand/finger tight and it should be fine. How cold is ti up there?

I just had to have my water sensor replaced on the bottom of the fuel filter. The bleed (drain) valve just started leaking (dripping) diesel and the valve has never been opened. It started losing its prime slowly and with a very slow drip out the valve.

all them stuff can be hand tight, the wif sensor can be wrenched on, but not too tight

An easy way I have found to see where fuel is bleeding off is to take a piece of clear hose about 7ft long and connect it to the inlet of the cp3 and to the hose connected to it. This way it is inline and just hang it from the hood. See which side leaks fuel down. That will tell you which way the fuel is going. That will help figure out where to start looking.

I had to do this also, truck kept losing prime.

Fixed now though, I must have bumped it or messed it up on the last fuel filter change.:U:

Well, this weekend my truck seems to have been running better, but I'm wondering if the WIF sensor as Danny mentioned might be starting to develop a mild leak. I ran all weekend with no more issues, but thanks for all the tips guys.

the wif sensor does use an o-ring to seal it up

help help please i have a fire dept truck 2007 with a duramax it wouldnt start, so one of the firement changed the fuel,filter,, pumped it all upm and bled it it started up and drove for that day , then after shut off it wont start , no fule presure on the rail at the shcrade vale at all, hand pump it a few time and it aill start and run f ro a few seconds then die, according to gm there isnt a pump in the tank on this 2500 and i cant find a rail pump either, id the only pump on this truck the injector pump? funny thing is this one of the fireman actully beat n the fuel tank and it started the tohter day (like a gas motor with a bad pump) help help im doing this as a free help thing for the fire dept as im so close to them , im kinda an idiot with thses engines..

there is no pump to push the fuel to the injection pump, the injection pump sucks its own fuel. the schrader valve is used to diagnose if the fuel filter is bad if it pulls enough vacuum.

make sure the filter is on tight and the bleeder screw is as tight as you can get it with your fingers. any tighter you run the risk of stripping it.

well the thing is it wouldnt start before the filter was put on as i am told, the filter was put on as an after thought. shouldnt there be pressure on the shrade vale as to tell me the fuel presure of the turck? i found when the hand pump is pumped a few times the fuel come out of the shrade valve and if i pump it several time it will start and run then die as it is out of fuel, aslo while it was running checked with the fuel pres reg to see iif it was wroking and it is, is the only pump on the duramas the cp3 injector pump? and it sucks and presurizes the rail ? im used to some of the fords (im sorry) they have a rail pusher pump or a high and low prsure pump,,,, im not ever really had to do much to the duramax

wait the fuel comes out the schrader valve when you prime the system?
thats not supposed to happen.

the way they use the schrader valve for diagnostics is that they hook up a vacuum gauge to it and see how many inches it pulls.

the injection pump sucks its own fuel from the tank, though the filter, past the schrader valve into the pump.

is there any check engine lights? or any blown fuses

with the shrade valve open and i hand pump the primer on top of the fule flieter and water checker yes fule dribbles out of the shrade valve yes yes

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so on this unit the shcrade valev is used for vacume only on the sucction side then? and not used like the other systems where i can run and test fuelk presure on it?

if your shrader valve is leaking you could be sucking air into it causing issues.

i mean the shrader valve as in the one next to the alternator, not the bleeder in the top of the fuel filter housing.


you could get a pair of very small vice grip pliers and pinch shut the hose that goes to the shrader valve cause it tees off from the main supply line that goes from the fuel filter to the injection pump.

yes.

well the reason there was fuel ablt to come out of the shcrade valev was because i had it open to see if i had any presure , but if it is for vacume daaaa silly me , i thought it was a presure port , ok well here is the deal then if i under stand this m the fule from the tank (no pump in the tank or in the line) is fed through the line to the cp3 pump , (sucked) by the pumpe and fed into the rail , the srade valve is on the suction side of the syatem so i should have a small amount of vacume at cranking then?

yup

i think they change filters at 15in vac. iirc:humm:

what really aggrivated me is that even giving gm and the local parts stores both, the vin number both gm and the locals said oh there is a fuel pump module in the tank, and inspecting the wires to the unit there are two wires to it and im sure they are for a sending unit and no pump , even gm said they could send me a pump unit that went into the tank , how silly this is sorry but im a virgin with a duramax:s:

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is there any service port or any way to test to see if i am getting any presure on the rail side ? and also is the cp3 pump a mechanical driven pump? or is there a way to check it?

two wires is for a rheostat, your fuel lever sensor.

there is a few places that can cause a leak, on the bottom of the fuel filter there is like a 16 point plastic nut, that could be loose or not right enough. be careful though, it has plastic threads.

or the water drain valve, or the bleed screw not working right. hell even the fuel filter could not be on tight enough. loose lines, or schrader valve could cause leaks.

you can prime the system really good, and then get some soapy water and spray it all over the place and see if you can find leaks

yes i figured as much on that but it was silly that even gm with the vin claimed it as a pump

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i will try that in the am and return , thanks so much , ill have me or one of my crew recheck the fire dept work on this thing tha:s:nsk

where you located

southern illinois

another issue, soemtimes the fuel filter can be accidentally be missing gaskets, or double gaskets.

i would also remove the edge too

and pump that primer on top of the FF untill its rock hard

yes i am aware of that as well ill be checking or one of the guys will in the am but i think the no start was before the filter was installed , then they tryed a filer

hmm...

any smoke when trying to crank, or fuel smells?

most common problem is, a cracked fuel filter housing, or cracked water in fuel sensor.

no nothing it just cranks until i pump the plunger on the filter then it will strt and run till it runs out of fuel, the other day when they said it wouldnt start etc then they changed the fuel filter they primed it and it started as well they said they drove it for a couple times then when parked it it wouldnt start unless its primed at the fuel fileter pump , when it runs out of hand pumped fiuel it dies:scare2:

yeah, definitely sounds something is cracked, prime it up and give it a good look for any leaks. on the fuel filter housing and bleed screw and where the filter meets up with the housing.

you might have to pull it off, two 12mm bolts hold it on to the valve cover

i will check and see is there only 1 type of pump on this duramax? the cp3 pump? or is there some sort of secondary unit, i figure in the am we can check the fuel syatem for some sort of leak or open ness or oring etc

tell technically its two pumps in one, but the cp3 pump( injection pump) is located in the valley of the engine in the front.

so tech speaking if i have or cant find any leaks i need to look at the cp3 pump unit as it is the only type of fuel pump on the truck?

yup. but thats should be ok, i seruoisly think its just a crack.


the cp3 pump has a suction pump thats integral.

there is no smoke of any kind while cranking it is not getting any fuel

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ok well we have replaced the fuel filter with a brand new one tryed to check and recheck the wif on the bottom, we repalced the sping type hose clamps on the lines to the filter with the good gates clamp srew downs , primed it up , so far its been running for an hour , but the guys from the dept said it did the same thing the other day so we will see

Did you get the truck fixed?

yes thanks to all, i had one of the techs remove the whole filter assembly , we removed the wif and everything resealed it put a new fuel filter on it , replaced the factory sping hose clamps with srew tighting clamps and made sure the cap was tight on the schrade valve, pumped it up and let it ran, cleared the codes and so far its been fine thanks to all:jump: