My 2004 loses its fuel prime when it sits overnight. It has an aftermarket lift pump and I have the priming circuit on a toggle switch so I can turn the lift pump on with the engine off. I can prime it for several minutes and it's still hard to start and when it does it makes that clattery sound it makes when it's starved of fuel. This makes me think the problem is downstream of the filter? Is there a pressure relief valve or something in there that could be the problem, or do I have a leak? I can't find any fuel leaks and there's no fuel in the oil.

Thanks,
Nick

 

Could be a high pressure leak (lines, connecting tubes, injectors), or a bad CP3 (injection pump).

 

how could it be a high pressure leak? when the truck is shut off the pressure is released from the rail. there is still fuel in the rail, but its not pressurized.

 

Bump

 

there has to be something like a valve or i dont know what that keeps gravity from pulling the fuel back into the tank. maybe that has gone bad. look up the whole fuel system, like a diagram with parts labled and maybe that will help you see possible places where the fuel could be leaking.

 

You don't know you are losing prime. You are guessing. Gauges on the fuel feed line and on the high pressure rail would be definitive. At the moment you are chasing your tail.

 

So I'm still having this problem. I found that when I plugged it in it would start fine. I also tested and examined the intake heater and relays and they appear to be fine. A mechanic friend of mine said that on older rigs the heater could get coked up but mine is clean. Any ideas?

 

So you are saying you have unusually long crank times or unusually difficult cold start especially when not plugged in?

I would bet it turns out the injectors are shot.

The injectors normally have some return flow. That runs out of a fitting at the back of the engine, joins return flow from the high pressure pump, and is routed back to the tank.

As the injectors wear, their rate of return flow increases, and if it gets too high, the injector pump won't be able to pressurize the rail high enough for the ECM to fire the injectors. This seems to show up first as long crank time when starting a totally cold engine.

Here is a video that at around 3 minutes in describes the process of measuring injector return flow.

 

What ended up being the problem?