Lift Pump

[ak diesel driver]

So I have been having an occasional hot start issue and I think I have it narrowed down to the LP. Previously whenever there was any temp showing on the guage I'd never wait for the WTS light. A couple of times now it almost hasn't started (or at least seemed like it). So I threw on my mech pressure guage on the drain t and started monitoring it. It has great fuel pressure, about 6psi at idle and never goes below 3.5psi at wot. But what I have been noticing is that the pressure is bleeding off quicker than I think it should when I turn off the truck. That varies too, sometimes 1 or more hours and once it dropped 3lbs in about 5 mins. So my ?s are (for those with guages) how long does a typical bleed down take and does anyone know of a cheap check valve? I do have a walbro to put on but I'm cheap and with the good fuel pressure it puts out I'd like to milk every last hour out of it. BTW this LP has lasted far longer than any of the others I've had. Before this one I'd be lucky to get 1 year this one has been on so long I can't remember exactly when I put it on probably 2-3 years ago I think.

 

[buddy]

Is this on the 96? If you crank right away you lose glow help as well as LP priming that OBD2 does during WTS.

 

[Acesneights1]

try pouring water on the IP when this happens. A worn IP will lose head pressure when hot. My Tahoe used to do that. The IP was on it's way out.

 

[ak diesel driver]

yep and yes I realize I'm losing glows and lately the priming. The couple of times I have cranked it warm with the pressure guage installed it acted like the LP wasn't working while cranking or at least couldn't catch up quickly. I was also wondering if my vac in the fuel tank could be hindering the pump. It might still be at full vacuum but the check valve has let the pressure bleed off.

 

[ak diesel driver]

try pouring water on the IP when this happens. A worn IP will lose head pressure when hot. My Tahoe used to do that. The IP was on it's way out.

You'd think it would do it consistently then. It's random now

 

[Acesneights1]

Mine started as random. Only when very hot did it become consistent. Just offering my experience.

 

[bison]

Ak,these LP checkvalves are mediocre at best. My wife's 95 truck has a good LP but it still loses pressure fairly fast at times but after 5 min its always gone.
On my own truck the pressure disappears as soon as turn off the key,but being it a 98 it comes on again as soon as i turn the key on
On the 95 i got an LP over ride switch that she flips on to pressure the LP in the morning.

That being said No pressure at start is not realy a problem as the fuel system is closed loop,what would cause a problem is if air enters somewhere and causes the bleed back.
Do you got a clear return line on the LP?
That'll tell ye if it's air causing it.

 

[buddy]

The PCM will prime the system automatically during WTS if you let WTS run. Thats part of the waiting, for the LP to prime the line to make starting easier.

 

[ak diesel driver]

I do have the clear line on my IP but I can't see it with my hand on the keys lol. I guess I was just spoiled not having to wait for LP to pressurize

 

[bison]

look at the hose before you start. As you know,no fuel means air intrusian and bleed back.

 

[ak diesel driver]

I see what you mean. Any idea why it would be intermittent?

 

[bison]

Nope,could be anywhere.
Loose hose clamp,crack in a hose,inj return hose, clear tube getting hard.filter.
IP shaft seal.