I was diagnosing the full throttle miss and stumbling problem my truck recently developed in my driveway, by opening the T-valve to check for fuel flow from the lift pump. Well, it turns out that was my stumbling problem: no fuel at all came out. Not a drop! And sure enough, the engine stalled after about 15 seconds with the valve open.

Now here's the strange part: when I turn the key to the wait to start position, I can here the lift pump purring away to prime the system, then it stops purring, like it's on a timer, which I think it is supposed to do. However, when I leave the T-valve open to check for fuel while the LP is purring, no fuel comes out. I tried it like 10 times, and not a drop. I thought maybe the engine drew all the fuel out of the filter bowl with the T-valve open, and it would take a few tries to get fuel to flow out, but nothing. I was suspecting maybe the OPS was the problem, but now I'm thinking maybe the lift pump is bad, even though it is purring like it is working? I just replaced the lift pump myself like 5k miles ago. The old one was dead - no purring, nothing. Can lift pumps purr like they are working, but not pump anything?

A more pressing problem is the truck now won't restart after it stalled with the T-valve open. I closed the T-valve, tried several cycles to get the LP to prime the system again, but it won't fire at all. Doesn't even try to catch, like not a drop of fuel is getting to the engine. The problem is the truck is in the driveway, blocking my garage so I can't get my other car out to go to work tomorrow :(

Is there anyway I can manually prime the fuel system to get it started again? Or am I screwed without a functioning LP? :help:

Obviously the LP is no good....you might be able to take the filter out of the housing and fill up the housing with fuel to get started.....

OBDII purrs with key on then stops after about 5 sec, PCM is looking for crank sensor input after that to indicate to PCM you are actually trying to start the engine.

The pump can purr and still move no fuel, look at the dissected pump pics I did earlier this month or maybe last month, the plunger could purr but if the valve seats on the end of the plunger were shot it wouldn't move any fuel.

I healthy IP can draw it's own fuel performance would suffer on the top end without the lift pump assist, some trucks with a worn IP won't start without a lift pump assist

better off replacing the LP and saving the IP.

If you're in a real pinch and need to start the truck, get some suction going at the bleeder valve (shop vac, hoses, duct tape).

take the top off of the bowl and fill it with fuel, suction is from the bottom of the filter bowl, if batts are fully charged extended crank should be able to get you restarted

Crappy defective lift pump! what luck! It is a new AC Delco too - I thought they made good stuff. Guess not. :( It's tough to find anything made with quality these days. :mad:

I checked the fuel filter and it was clean. I tried running the LP with the filter out to see if the filter bowl would fill up with fuel. Not a drop came in. So I think you're right - LP is dead despite its purring. Something must have broke inside it besides the solenoid which is still working making the purring sound. It's probably some 5 cent made in china part that some bean counter thought made good sense to use in it.

I wasn't able to get it started, but was able to push it down my driveway far enough to get my car out of the garage tomorrow. I have no idea how long the LP has been inop on my truck. I only discovered the problem when I went to WOT trying out my new exhaust (I rarely go WOT with my truck, I generally baby it). I hope I haven't damaged the injection pump too much by driving it without the LP working. Man, I've only had this truck for 9k miles and I've had lift pump issues TWICE now, and I haven't even had to deal with the OPS yet.

It's possible your OPS is killing the lift pump, by causing too much current draw, next time replace OPS & the pump, also make sure you have a good solid ground for the lift pump

Take the bleeder off the filter,while installed, and use a squeeze bottle to fill the filter cavity. Works every time.

It's possible your OPS is killing the lift pump, by causing too much current draw, next time replace OPS & the pump, also make sure you have a good solid ground for the lift pump
I thought of that possibility, but it seems to be a mechanical failure of the lift pump, not electrical because it still purrs like it always did, just won't pump any fuel.

Thanks for everyone's help and advice. :) I'm off to the dealer today in search of a new lift pump. I'll post the outcome here as soon as I get the new pump on.

I'm happy to report a new lift pump from the dealer fixed all the problems. Put a new filter on too, just to be safe. Got it started, pumps fuel through the drain valve during startup and while running (OPS OK), and runs great! No more stumbling or missing at full throttle, starts faster, and a bit more power.

I'm pleased that this fixed the problem, and was a relatively easy fix, but I'm a bit ticked off and surprised that a new lift pump failed after only 5k miles and 8 months. I was wondering if maybe I had a counterfeit Delco pump? Has anyone heard of these? The reason why I was thinking of this possibility, besides the premature failure, was the broken pump didn't have the same markings on the outside metal housing that the new pump had. For example, the new pump has a flow arrow engraved in the metal, which the old pump did not have, and the old pump had some strange silver tape on part of the housing, as if it were covering something up. I want to take that tape off and see what's underneath it. I bought the old pump online from a reputable supplier, and it came in a Delco box. This new pump I bought from my local dealer, and also came in a Delco box.

Thanks again to everyone who helped diagnose the problem. This site rocks! :ro) :cool2: