Fuel pressure problem

[laserjock]

So I have a really strange problem. My fuel pressure at the filter head drops as the truck warms up. New fuel lines. New fuel filter. New facet 40222 pump.


When I cold start it, it's at 8-9. By the time it's at operating temperature it's 0.

I unscrewed the fuel caps so I know it's not a venting issue.

I switched tanks. Doesn't seem to matter.

I don't think there is any correlation to run time but I'm not sure.

There seems to be a correlation to temperature but I'm not sure.

This screams either lift pump or air leak to me but I don't know.

There's no way this is an IP issue right? It seems like once I mess with things to get a little fuel pressure it will start again.

First thing I'm going to do is add a section of soft line between the lift pump and the supply line in case the fitting is working loose. I found that fitting loose before but it did not seem loose this time. Not sure where I'm going from there.

 

[abepratt]

First thing I'm going to do is add a section of soft line between the lift pump and the supply line in case the fitting is working loose. I found that fitting loose before but it did not seem loose this time. Not sure where I'm going from there.

Great idea. Use clear line then you can see if you're sucking air somewhere by the air bubbles...



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[no mufflers]

im sure its not something you want to do but you could put the factory lift pump back on. most of the time hot mine will only have 1 psi.

 

[laserjock]

The thing is I can see it's still pumping fuel. You can see it running into the clear fuel bowl. Level really doesn't seem to drop.

 

[Thewespaul]

Check your power at the lift pump make sure it's not an electrical issue first, then I would blow air through the lines and replace a fuel hose with a clear hose as said above. Hope you can work these gremlins out soon!

 

[laserjock]

Let it cool for an hour. Pressure back to 6 psi.

 

[OLDBULL8]

Defective pressure gauge?

You don't say whether it stalls or not, Idling or running.

 

[laserjock]

My wife and google for the win...I think. She's googling asking me questions. She says do you have a liquid filled gauge. I said yes. She says I'm seeing a lot of posts saying liquid filled gauges can cause low fuel pressure when they get hot. I said really? So. Fire the truck up and set the high idle. It's at 6 psi. Close the hood let it get hot. Down to zero. Put ice pack on gauge. Creeps back to 6 psi.

So that may not be why it's dying but it solves the fuel pressure mystery.

 

[catbird7]

Shouldn't the clear fuel bowl be "full" with pump running? Could it be a small air leak somewhere before the pump? Any poor connections after the pump should show up as a fuel leak because fuel is being pushed.

 

[no mufflers]

I was going to say you could just let the pump run for a while with the engine off. I guess just to find any other problems.

what happened when it stalled? or what did it feel like made it stall? if it was starving of fuel I would think if you ran the pump for a few it would start.

 

[junk]

I hate to say it, but have you tried cooling the injection pump down when it dies? That's a typical heat soak test. I know you have a new injection pump, but as you seem to have fuel pressure it leads me to the injection pump. Does it die returning to idle or just turn off? My 93 would die returning to idle if i don't run a fuel conditioner in it. Might try adding some lubricity to the fuel.

I believe you said the FSS was working?

When I've ran my truck out of fuel it surges before it quits.

 

[shawn deere]

My wife and google for the win...I think. She's googling asking me questions. She says do you have a liquid filled gauge. I said yes. She says I'm seeing a lot of posts saying liquid filled gauges can cause low fuel pressure when they get hot. I said really? So. Fire the truck up and set the high idle. It's at 6 psi. Close the hood let it get hot. Down to zero. Put ice pack on gauge. Creeps back to 6 psi.

So that may not be why it's dying but it solves the fuel pressure mystery.

Thats odd. Wonder whats going on there...

Also have you checked voltage at the pump cold and hot? Mayhaps the electric motor is pulling way more juice than it should

 

[laserjock]

That's next. Picking up a regular gauge and I'll warm it up again and see if I can get it to do it. Need to see if I can replicate the condition.

 

[laserjock]

I honestly am wondering if it's a venting problem now that I know it may not be a pressure problem.

 

[FORDF250HDXLT]

Yeah that's what I was thinking.That or a fuel return line issue with a pinched line,failing return port of the selector valve etc.You don't really need a fuel pressure gauge as we only need something to feed the ip so there's no vacuum.The "fuel filter" light is pretty much all you need.If it's stalling out but not sucking air then it very well could be and probably is the return somewhere.Though why only when warm? What the heck does this help point to? Interesting.Can't wait to hear what you find.

AH.I got it.....maybe lol.
Rubber line off the back of the engine that connects to the hard line.The return.This hose when it's gets warm from the engine heat is collapsing? That's all I got for now anyway.