1998 C2500, 6.5 losing prime

[joe bleaux]

Hi,

Back after a long absence.

After several days of not running the engine, the system loses fuel prime.
I have looked at all of the places whereby it could leak air/fuel but nothing found. Have changed filter, fuel pump and still cannot find it. I can clear it after unscrewing the black top on the mail filter close to firewall. Used to be able to clear it with the small, brass valve in front.

Anyone know where I can get a cheap blower wheel WITHOUT the motor?
RockAuto has them for 25 bux.

Thanks

Joe

[rameye]

the fuel pump has a check valve...so without a visible leak between the pump and filter you might be sucking air aft of the pump....that is to say a pinhole leak (its under vacuum, not pressure aft of the pump) would allow the fuel to leak back into your tank and introduce air.

I ran a piece of clear hose from the brass fitting back to the tank fill after purging all the air....after about 1 hour I started to get air bubbles in the line......further checking revealed bad steel lines on top of the tank were the cause, allowing air introduction.

anyway you can pressurize the lines from the pump forward and examine for leaks just by jumping the pump...any prime losing leak will show.

my .02

[joe bleaux]

Thanks for the reply, rameye.

So, it is the fuel or lift pump that has a check valve. This is the second lift pump and I THINK that I had the problem before this pump.

I will remove the hot wire from the pump and apply 12 v.d.c. directly and try to look for leaks forward of the pump.

You ran clear hose back to the 'tank fill'? What are you calling the 'tank fill'?

Thanks

Joe



the fuel pump has a check valve...so without a visible leak between the pump and filter you might be sucking air aft of the pump....that is to say a pinhole leak (its under vacuum, not pressure aft of the pump) would allow the fuel to leak back into your tank and introduce air.

I ran a piece of clear hose from the brass fitting back to the tank fill after purging all the air....after about 1 hour I started to get air bubbles in the line......further checking revealed bad steel lines on top of the tank were the cause, allowing air introduction.

anyway you can pressurize the lines from the pump forward and examine for leaks just by jumping the pump...any prime losing leak will show.

my .02

[rameye]

I unscrewed the tank filler (where you put in fuel) and dumped it back in...works.

The fuel and the lift pump are the same thing on these rigs...there is no "in tank" pump...it is sucked out of the tanl like a straw therefore as it is under vacuum it is easier to introduce air.

Mine was doing the same crap...making me nuts.....little tiny pinhole in steel lines letting in air.

Like I said forward of the pump you are pressurized...aft of the pump...vacuum.

Have fun

[joe bleaux]

Hi, Rameye.

Thanks for the clarifications. I have had this tank out twice.

Exactly, where were the pinholes?

Thank you.

Joe





I unscrewed the tank filler (where you put in fuel) and dumped it back in...works.

The fuel and the lift pump are the same thing on these rigs...there is no "in tank" pump...it is sucked out of the tanl like a straw therefore as it is under vacuum it is easier to introduce air.

Mine was doing the same crap...making me nuts.....little tiny pinhole in steel lines letting in air.

Like I said forward of the pump you are pressurized...aft of the pump...vacuum.

Have fun

[JTodd]

I developed pin holes in the metal lines on top of the tank. To solve the problem I ended up grafting in hose from the tank half way up the frame to make sure I got all of the bad area. Even though the line is under vacuum, you should see evidence of fuel leaking slightly. If air is coming out, chances are some fuel is also leaking.

[rameye]

The exact place I was leaking was from the sender assembly...mine looked awful!!!

Anyway a got a new tank, new sender/lift tube assembly and then got marine grade fuel line and ran it from sender to pump. The hose is not cheap...made to be under vacuum...and internally armored for a marine/exposed environment.

Very happy...no more troubles....just scrap the steel and be done with it!

[joe bleaux]

Jeff, thanks for your input.

Did you 'graft' in a flexible hose?

Joe


I developed pin holes in the metal lines on top of the tank. To solve the problem I ended up grafting in hose from the tank half way up the frame to make sure I got all of the bad area. Even though the line is under vacuum, you should see evidence of fuel leaking slightly. If air is coming out, chances are some fuel is also leaking.

[joe bleaux]

That whole solution sounds very expensive. I will have to take a cheaper route.

Glad it is working out for you.

Joe


The exact place I was leaking was from the sender assembly...mine looked awful!!!

Anyway a got a new tank, new sender/lift tube assembly and then got marine grade fuel line and ran it from sender to pump. The hose is not cheap...made to be under vacuum...and internally armored for a marine/exposed environment.

Very happy...no more troubles....just scrap the steel and be done with it!

[rameye]

Because I need this truck to be a "go to" vehicle whenever I do a repair I always go above and beyond...

for example: as part of this repair I also scraped down and repainted the entire frame, installed a new rear bumper (old one developed an nice rusty hole)...welded up part of the rear frame horn that had dissapeared with 2B stainless.

I could have gotten away with just a new cheapie sender $29 and some average hose $50 and been running just as well.

If money is an issue, do what it takes to get it on the road only.