fuel pressure loss puzzle

[vaj]

Have a JD 310d backhoe.

After sitting, seems to run for 20 sec or so then stalls out - as if out of gas. I then have to play with prime pump, bleeder screw above fuel water separator for a while to get it going. Once it is going, will run all day, but once shut off somehow loses prime and will only run for 20 sec or so until (what I believe) all fuel between injectors and filter/primer area is used up.

Some history and background.

1. I am a homeowner and machine does not get regular use.

2. Last month had tremendous chipmunk nest in engine department. They chewed through reverser hose leading to radiator which I replaced. I see no other evidence of fuel hoses chewed and do not see any diesel leaks. But, this is when I noticed the shut down for the first time.

3. I did change the fuel water separator filter this summer. Because of this "opening" of the fuel system I keep coming back to this as the cause --- somehow a bad filter lets air in only when off and parked. Filter by the way is basically a female o-ring slip on with a plastic 1/4 turn tightening exterior nut over the whole filter. I almost replaced this filter again but don't know how air could get in to this otherwise closed system anyway?? In other words with machine off, even with filter removed and replaced, shouldn't cause air to enter into any lines.

Appreciate any thoughts,
Tim

 

[davesl708]

Are you sure the o ring is clean? A little lint or dirt will let it suck air.
Double check the fittings.

 

[vaj]

so the thought is even a pin leak would let air in above the tank pushing diesel back to the tank -- and this could be at the filter fitting or some other section after the filter? Interesting and I will check it out.

 

[mikel771]

Tim: Assuming, "and we know what that spells", your fuel tank is lower than most of the rest of the fuel system. You have a classic pin hole air bleed back into your fuel
lines, not enough to leak on the pressure side line(those lines after and including the lift pump pressure side all the way to the injection pump, assuming your diesel/
gasoline fuel injected or carb if your gasoline n/a) or the suction side lines including the suction side of the lift pump, in short your fuel is drainning back to the tank
before the system can purge itself of air and/or the fuel pickup tube in the tank can be drainning causing a plug of air to get to your filter and shutting you down.
The worst experiance I had was on a 3208 Cat engine with the "early" rectangular glass filter, Cat started out using a tappered pipe nut in a tappered pipe hole in
an aluminum housing, well !, as soon as someone including the factory over-tightened the nut the hole would hair line crack in the tread area,the vehicle would
sit for 2-3 days ,start ,die or run for 10min -4hrs and die. enough history.

Try this, take enough new clear plastic 1/4-3/8-7/16 ? line run it from the filler cap hole(below the fuel level in the tank with the apporpriate fitting, line stem and
hose clamp to your lift pump. I.E.bypass all conections and fittngs on your machine, tank to lift pump, prime and start,run and watch for any air foamming or
bubbles forming, watch for 15-20 minutes if none, it tells you that the system you've bypassed is probably good 'MAYBE', now, shut down and watch clear line for
1 minute to 3 days if air is getting in from air leak ahead of lift pump(incude lift pump) then the problem is in the lines on the pressure side to the injector pump but
( not including the injector pump) the injector pump is a reservior and ultra high pressure system unto itself. If the fuel is not drainnig out after a day or two, then
your lift pump and suction side lines are the problem. Eliminate as best you can the sections of lines and fittings working back to the tank by start, run, watch. set
method untill you stop the drainage problem and don't forget the fuel pick-up tube in the tank.
Hope this helps:

 

[mikel771]

Absolutely, think about it, you have 1/2-1 pound of fuel pulling on a 7/16" line, fuel is around 900 times more dense than air at 14.6 psi !

 

[vaj]

Summary:

Brand new Baldwin filter in the garbage

Brand new $22 John Deere filter makes girl run nice.

Who would have thought??

Thanks for the advice.