LB7 wont hold prime.

[Richard Hurley]

I have a 2002 LB7 farm truck that just stopped after running for about a minute. Found no prime. Re primed, would not hold. Replaced filer housing same condition. Checked for noticeable low pressure leaks, found none. Blocked fuel outlet line at filter housing. Prime held fine. From a previous scan i was told i had 4 injectors in the mid 4 range and one below 2. Replaced all injectors hoping to kill 2 birds with one stone. No luck condition still exist. Would it be worth changing the FPR or should i bite the bullet and do the CP3? The truck ran fine prior with no noises, whines or hick ups. Thanks, Richard

 

[Will L.]

Did you check if the primer pump needs rebuilding? Thats most common error

 

[Richard Hurley]

Did you check if the primer pump needs rebuilding? Thats most common error

Yes sir, I replaced the filter / primer assy. What puzzles me is, if i block off the outlet of the primer pump it will hold prime all night. This tell me that the vacuum side is good. What could be bleeding down after the primer pressure leaves the primer? Prime bleeds away pretty quickly.
Thanks Will

 

[Richard Hurley]

Yes sir, I replaced the filter / primer assy. What puzzles me is, if i block off the outlet of the primer pump it will hold prime all night. This tell me that the vacuum side is good. What could be bleeding down after the primer pressure leaves the primer? Prime bleeds away pretty quickly.
Thanks Will

 

[Will L.]

Has to be a leak somewhere. At this point I would break out the smoke machine. Drain the line and charge it with smoke to find it.

 

[Rockabillyrat]

I tell all my customers to upgrade to a aftermarket lift pump on a duramax.

The best way to check for a leak is a clear hose on the suction side and look for bubbles.

I put ALOT of sending units in these trucks due to rust causing them to suck air. Normally we do a new sender, fass, and all new lines to the engine.

 

[Lennydmaxguy]

I would second adding a lift pump, but the good ones are expensive. You could maybe buy a universal 12 V pump and pressurize the fuel system temporarily to pinpoint the leak.