plumbing the Carrier pump-- unconventional

[jim_22]

OK, I have air intrusion, I do not believe it is o-rings and caps but would rather suspect it is somewhere under the truck, possibly the fuel pollack valve. I may not get to it until Spring. Since I have a new lift pump, I really hate to take it out of there. So I was thinking of plumbing a Carrier pump under the hood in parallel with the stock lift pump. The electric pump would not run when the engine is running but could still be used to prime the system before starting. Then if I get tired of my lift pump or it gets tired of me, I can yank it and cap it off and then hot-wire the Carrier. See anything wrong with this?

PS I suspect (but am not positive) that what happens to me is that from the lift pump to injection everything is fine. The truck always starts but then the lift pump delivers air from the line below it and it stalls. I think I can temporarily fix this by running a full tank instead of the nearly empty one that I usually do. It is not a fuel tank "shower head" problem because once I restart after the stall, it runs fine.

 

[lotzagoodstuff]

The only thing that I would see as a potential problem would be if the diaphram in the mechanical lift pump fails, you could fill your crankcase with fuel

Other than that, I think this is a fine temporary fix.

 

[jim_22]

So now I confirmed it... filled up the (brand new) rear tank and no start/stall problems even if sitting for several days. My air intrusion is bottom end somewhere (and no obvious fuel leaks that I see). And it is not the famous shower head problem. I wonder how many other cases have been misdiagnosed with air in the fuel filter blamed either on the lift pump or the top end. This is why with my brand new rear tank I put 10 gallons in it and ran for a few days without incident and when the tank got near 1/4 or so it sucked air, never when running but only on a cold start after sitting. I am certain the air sucking is below the lift pump and outside the tank.

 

[lotzagoodstuff]

In order to confirm your diagnosis, I think you'd need to pull your old mechanical lift pump, or plumb a gauge on the suction side of your lift circuit. It is possible that your old lift pump is worn out and incapable of priming itself once the tank is lower and you've lost the head pressure that a bigger fuel load provides.

That's one of the advantages of the Facet electric pump: it "pulls" fuel much better than a mechanical pump, and you can physically hear when the low pressure side of your fuel system is primed.

If you really want to confirm your theory, I would install a new mechanical pump and see if you're lower than 1/4 tank issues continue.

Good luck