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D4 6U Low Fuel Pressure

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2 months 1 week ago #230605 by Keltonc87
 

 

 

So I have a issue with low fuel pressure currently. The dozer was in a fire and just got hot on the left side where the fuel filters are. Before the fire the fuel pressure used to peg the gauge, I’ve changed the fuel filters, rebuilt the transfer pump and check tolerances, replaced pressure return spring and plunger. With the pony motor cranking it over it’s got about 5psi and won’t start. I know the pump is getting fuel but it’s bleeding off somewhere. I was wondering if it’s leaking between the filter housing and the infection pump, I can crack the fuel lines and fuel comes out but not a lot of pressure. The dozer did start once but fuel pressure was about 10psi. Then tried to start it 6-8 months later and nothing 
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2 months 1 week ago #230606 by neil
Replied by neil on topic D4 6U Low Fuel Pressure
Check how well the relief valve in the transfer pump is sealing - it might have melted a bit

Cheers,
Neil

Pittsford, NY

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2 months 1 week ago #230608 by Old Magnet
Replied by Old Magnet on topic D4 6U Low Fuel Pressure
Are you getting fuel in the main engine sump? That would indicate the tower to injection pump seal is leaking.

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2 months 1 week ago #230609 by Keltonc87
Replied by Keltonc87 on topic D4 6U Low Fuel Pressure
 It should be sealing perfect, I replaced the relief valve and spring and also machined the surface as well. 


 

 

 
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2 months 1 week ago #230611 by Keltonc87
Replied by Keltonc87 on topic D4 6U Low Fuel Pressure
Yes, with the main engine cranking it has about 5psi and I can crack the bleeder on the top of fuel tower and fuel comes out but now under a lot of pressure. Also the injector lines have fuel coming out but not at much pressure 

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2 months 1 week ago - 2 months 1 week ago #230621 by trainzkid88
Replied by trainzkid88 on topic D4 6U Low Fuel Pressure
bad injection pump seals. put a full seal kit through the injector pump they can just fail.and since it got burnt it may have ruined the seals.

did you check the relief valve seat a new valve with a poor seat wont fix any thing
Last edit: 2 months 1 week ago by trainzkid88.

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2 months 1 week ago #230638 by edb
Replied by edb on topic D4 6U Low Fuel Pressure
Hi Team,
if you have low pressure fuel issuing from the injection pumps then the rack is in the closed position. The operators lever sometimes needs a good tug backwards to get past the shutoff detent inside the Governor which could be likely due to the heat gumming up the oil in the pump and governor housings.

Failing this then you have either a stuck rack or stuck injection pump plunger NOTE resist the urge to rotate the inj. pump plunger by forcing the rack as it is possible to rotate the gear quadrant on the inj. pump plunger and loose the factory test bench set fuel delivery setting rendering the stuck pump useless without a proper test bench to re-set said pump up on.
Spray the inj. pump plungers with your favorite loose juice and gently pry the stuck inj. pump lifter up and down by its yoke--some very gentle tapping up and down may assist--stuff in the side cover of the injection pump is very hard steel and so is fragile.

If your Inj.pumps have the bleed screw pictured in the scans these need to be bled too for easier fuel bleeding to thee injectors--later Inj. pumps do not have the bleed screw and are self bleeding due to changes to the hollow dowel that sends fuel to the Inj. pump body.
The Inj Pump seals will appear triangular in shape when removed as this is the shape they attain after years of being crushed in situ--the replacements are round O Rings as were the old ones when originally fitted--same for the Inj. pump main body fuel gallery dowel O Ring at the fuel tower.

Let us know what you find and we can assist further.
Cheers,
Eddie B.
The following user(s) said Thank You: juiceman, outbackrider, trainzkid88

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2 months 6 days ago #230697 by Vance Nickerson
When my D47U sits a while the pump plungers stick and definitely give the linkage a good tug as I missed a show from that simple thing last year.

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2 months 1 day ago #230847 by Keltonc87
Replied by Keltonc87 on topic D4 6U Low Fuel Pressure
Thanks for all the info, I’ve bled out all that air that I know of, I’ve cracked the lines at the injectors and fuel comes out pretty steady. According to the pressure gauge I’ve got about 4psi at the filter housing. I was wondering if the seal could be bad between filter housing and injection pump and if it’s bleeding fuel into the crankcase. 

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