Got an 08 6.4 that after driving, park it on an incline with driver side down, it wont start. Fuel gets aerated. Bleed the high pressure side, it'll start and run, until parked driver side down (wont do it pass side down). Tank unit replaced, low pressure pump replaced. All lines and washers ok and tight. (SO YOU WANT TO BE A TECH?)

 

This may be a dumb question, but where are you seeing the aerated fuel?

 

P2291 (low FRP) Use tool in high pressure line, lots of air bubbles.

 

Very interesting problem.

I figure the problem can't be on the high pressure side because there is a huge amount of pressure in those lines; a hole there would squirt fuel outward rather than ingest air into the lines.

The low pressure side operates at a much, much lower 3 PSI of pressure, so it's much more likely the issue is on this side.

And if I remember right the secondary fuel filter is on the driver's side of the engine. Now I'm not too sure how the fuel flows inside the filter housing, but I'd guess either an improperly installed filter or gasket. If not that I'd guess something awry with the filter housing...

Am I even close?

 

Nope, fuel filter is in the middle. FRP is in the high side. Air comes after the high pressure pump, at the cooler.

 

I see...

I knew the FRP was on the high side, but I figured that because air compresses far more than fuel that the pump could ingest air and thus not be able to build enough pressure on the high side.

So it was the fuel cooler? I thought the fuel cooler only cooled return fuel coming from the HPFP as it went back to the HFCM and tank... Aerated fuel returning to the HFCM would be recycled back to the HPFP I think.

But you implied that the problem had nothing to do with the low pressure side, so now I'm confused.....

 

What about the fuel cooler system?

 

You do the bleed procedure at the fuel cooler where the return from the high pressure pump is.

 

Disregard my last post.

 

Fuel cooler is okay.

 

In all other aspects (on flat ground and all other the scenarios) the HPFP is good right?

 

Warranty........cant just replace parts. Gotta have proof and prior approval.

 

I wasn't saying throw parts at it, I was just asking if the pump was performing at normal standards while on level ground, normal driving conditions, etc.

 

Yep! Runs and drives fine, no misfires, plenty of power.

 

How can air get in, but fuel does not leak out? There must be a backflow/pressure relief or something like that somewhere, right?

Maybe a fuel injector, when there is no ignition power, is allowing compression to go back into the fuel system? Just happens to be on the driver side of the motor?