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1991 f-Superduty fuel delivery


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LOSTbutAMBITIOUS
User

Mar 8, 2010, 11:12 AM

Post #1 of 7 (3121 views)
1991 f-Superduty fuel delivery Sign In

I have a 1991 Ford F-Super Duty (450) 7.3L Diesel with 258,XXXmi. I seem to be 'losing prime' in the fuel pump overnight. Yesterday I pulled off the fuel pump and manually pumped fuel to the pump, and filled the Fuel/Water separator then it started fine all day. this morning I'm having the same problem I had yesterday before I did all that. I can't see any fuel leaks so I have no idea where to begin. Any suggestions for 1st, 2nd, 3rd culprits and so on? I just don't know where to start spending money because it's limited (the money that is) and I can't afford to replace everything from the fuel tank forward if I don't absolutely have to.


(This post was edited by LOSTbutAMBITIOUS on Mar 8, 2010, 11:13 AM)


nickwarner
Veteran / Moderator
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Mar 8, 2010, 7:00 PM

Post #2 of 7 (3112 views)
Re: 1991 f-Superduty fuel delivery Sign In

You don't have a normal fuel pump like a gasoline system. This is a mechanical injection system which uses a lift pump (much like a carburated mechanical fuel pump) to supply fuel to the injection pump assembly. The injection pump generates tremendous pressures (several thousand PSI) when the engine rotates to a particular cylinder which pushes the injector off of its seat and releases atomized diesel directly into your cylinder to cause combustion. There is a primary and a secondary fuel filter, which filter at different micron levels. The primary is usually on the suction side of the lift pump, and the secondary filters to a finer level prior to entering the injection pump. What can be happening is the gasket isn't holding well on the secondary fuel filter and loses pressure. If you were sucking air it would be the primary. You didn't list how regularly you change these filters, but bear in mind that semi trucks change the fuel filters out at every service. While this may be unneeded for you I would consider doing it every other service. Be sure to lubricate the gasket and fill completely full of fresh diesel fuel prior to installation.


LOSTbutAMBITIOUS
User

Mar 8, 2010, 9:05 PM

Post #3 of 7 (3109 views)
Re: 1991 f-Superduty fuel delivery Sign In

I just replaced the fuel filter (secondary? big one looks like an oil filter says fuel/water seperator) and oiled the seal then hand-tightened. Where would the other fuel filter be?


nickwarner
Veteran / Moderator
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Mar 10, 2010, 7:47 PM

Post #4 of 7 (3094 views)
Re: 1991 f-Superduty fuel delivery Sign In

not sure of exactly where it is on your truck offhand. If you hook a hose to the lift pump and put it into a fuel can to fun it, try this; get some UV dye at the parts store that is compatible with diesel. Mix it with the fuel in the can and run the engine. Shut off the lights in the building and shine around with a black light. Any leaks will contain dye that lights up like a roman candle under a black light.


LOSTbutAMBITIOUS
User

Mar 12, 2010, 3:56 PM

Post #5 of 7 (3082 views)
Re: 1991 f-Superduty fuel delivery Sign In

Okay, will try. Could just try in fuel tank?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Mar 13, 2010, 4:56 AM

Post #6 of 7 (3081 views)
Re: 1991 f-Superduty fuel delivery Sign In

I'm not a diesel expert but in looking up parts could only find one for this application. The water separating oil filter looking one like this,



If more than just a pick up screen/sock in the fuel tank I can't say,

T



LOSTbutAMBITIOUS
User

Mar 14, 2010, 12:46 AM

Post #7 of 7 (3071 views)
Re: 1991 f-Superduty fuel delivery Sign In

Yeah - that's the only filter I could find as well.






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