Engine/Transmission (1998.5 - 2002) Fuel pressure during Wait to Start

[EEJ]

I have a 2001 3500 with a Fass DDRP and Big Line relocation kit that was installed about a year ago. A few weeks ago, I installed a Westach fuel pressure gauge. At idle it's running 18-20 psi. When I turn the key to the on position, the pump will for a second or two and build to 18-20 psi, but the pressure will immediately bleed off. I would assume that there is supposed to be a check valve somewhere to keep pressure. I searched the service manual but couldn't find anything. Is there supposed to be a check valve, or is this normal?

 

[mweiman]

As far as I know it is normal, mine drops off the same way with a factory lift pump, as does my brother's with a Fass 95. Any truck that I have ever checked fuel pressure did the same. I would say nothing to worry about.

Matt

 

[JLandry]

Diito here. Mine does the exact same thing.

 

[Ncostello]

The return line at the VP inlet has a pressure relief valve on it... so thats probably not letting anything bleed off if its all good. Its perhaps bleeding off thru the VP pump and that return line from the injectors... or just back flowing thru the lift pump setup. I doubt any of the common lift pumps have reverse flow check valves in them.



Doesn't take much of a flow path to bleed off pressure in a small diameter line since there isn't that much volume there. This was normal on my 99. It'd go back to zero pretty quick once the pump stopped.

 

[Bob Cochran]

Though I don't have a Fass mine bleeds off also.

 

[Road Dog]

My understanding is that the lift pump doesn't run until the starter is started. That's why you bump the starter to charge the fuel system.

 

[JMetzger]

Mine does the same thing. I believe turn key on & pump runs for 1-2 sec & then does not run until you engage starter or bump starter then it run for 20-30 sec. Mine bleeds off the min the pump stops, always has even with OEM pump or the FASS 95

 

[John - K5AWO]

Normal operation.

Drops off about 2 seconds after pump stops.

 

[jeepit]

Normal. Mine does the same.

 

[LSchulz]

One more vote for that being normal. OEM lift pump cycles for a second and builds a little pressure, but falls back to zero until you hit the starter, and then the lift pump will come back on.

 

[Ncostello]

Road Dog... the lift pump will run for about 3 seconds upon "key on". It will run for about 30 seconds if the engine senses a "no start" condition... which is why people bump starters to prime filters. Longer run time. And it remains on constantly with the engine running. If you get in a wreck and the engine is disabled (without turning the key off) it will continue running for about 30 seconds then shut off.



I got a Deutsch connector to match the harness connector... and I made a set of leads with clips on the other end. I used to plug in my lift pump to this and hook it to my battery and let the lift pump run for a few minutes when I did filter changes in the garage. I never liked bumping my starter if I didn't have to.



The same Carter lift pump is used on ISC 8. 3L Cummins engines with much better success than ISB 5. 9L's. On the ISC's... the Carter runs for about a minute upon start up... then shuts off allowing the CAPS injection pump to assume "pulling" fuel duties. Unfortunately the VP44 was no designed to pull significant fuel for itself... so the electric pump has to run constantly... thus wearing it out faster.

 

[ALepley]

Same thing here

 

[JCyrbok]

same thing here too, its normal.



J-