HELP! Losing prime in a couple of hours

[Dieselnerd]

In an earlier post, I mentioned losing prime while on a trip. It's progressed to the point where if it sits for a couple of hours it will not start unless cranked for awhile or primed by hand. I have new fuel hoses ready to install but the old ones look perfect. No cracks or rot or leaks of any kind. Before I tackle that nasty big job of changing them, I have a few questions for you experienced problem solvers.

1. When I prime by hand, I can pump the button for a while until it becomes hard to push and I hear a noise that sounds like a relief valve opening. At this point it will start right up. If I leave it sit for a minute or so, without starting, and push the button again, it's easy to push and takes a while to become firm again. Is this normal or am I losing the pressure I built up?



2. If I remove the rubber cover from the lift pump primer button, the rubber cover has fuel inside of it. I don't think this is normal, is it?



3. Once started, it runs great. This is the original lift pump and I know they made several improvements since 1996. Will a lift pump going bad cause you to lose prime or am I barking up the wrong tree?



4. I imagine the delivery valve could also be going bad but I have not lost any power and everything seems normal when driving.



I hate to throw parts at it without narrowing the problem down a little more. Any and all help will be appreciated.

 

[Lnwing]

losing prime

Dieselnerd,



Several years ago I had a similar situation on my 95. Warranty was still (barely) in effect, so I took it to the dealer.

They checked it out and could not find the source of the problem, so concluded that it was in the pump and sent me to a local Bosch pump shop. When the pump checked out fine, the mechanic at the pump shop found that it was indeed a hose problem, even though it looked fine. He replaced the hose and fixed the starting problem.

Good luck!!



Lnwing

 

[illflem]

Sounds like the o-ring on your lift pump primer button is leaking causing the loss of prime. The o-ring is the only repairable part of the pump, new one will set you back less than $1 from the auto parts. If your hoses have never been replaced you should do the nasty, it's just a matter of time...

 

[Dieselnerd]

Thanks guys, everyone seems to agree that the hoses have to be changed and I will do that for sure. Sounds like that "O'' ring is the culprit. It didn't seem right to have the fuel seepage under the rubber cover. This happened at a bad time since we just sold our old Blazer and the truck is our only ride until we take delivery of a new vehicle next week. Murphy's Law for sure. I'll pull that "O" ring and replace it. After we have our second vehicle I'll tackle the hoses...

 

[pwknapp]

What size is the o-ring or a part # so I can pick it up before taking the old one apart? Mine is leaking at the pump bulb also.

 

[Joe G.]

The stock O ring is kind of oval in the shape of the rim instead of round. A round one works just fine. I took my old one into NAPA and bought the closest match. No leaks in a bunch of miles since. I think the price was 51 cents. I think I remember a smaller one involved somehow. If there was, I replaced both. It's been a while as you can see from this ramble.

 

[Taz]

I'm having the exact same problem. I don't know about any fuel around the lift pump, but I will check that today.



Another thing that can cause this, and has caused mine in the past is the fuel return check valve spring in the injection pump. The spring becomes compressed and will return fuel to the tank and loose prime in the injection pump.



I'm going to check my lift pump today. I'll post my findings.