I just went out and confirmed mine drops back to 0 about 2 seconds after you switch key off.

 

Wait, what are you observing that isn’t changing? Pressure? Volume? I thought the problem is excessive pressure drop when fuel demanded by the injectors increases.

 

Yes, pressure drops under demand. At idle is below spring rating.

When key is turned off, or leave key on after 20second pump time out, holds pressure at about 20lbs.

 

So you went for a drive with the pump sucking from a 5-gal can and there was no change?

 

KOEO sitting on the floor in my shop.

No change in regulated pressure 60ish pounds.

No bleed down in pressure below 20lbs once the pump shuts off.

That would indicate to me that whatever the restriction is causing low pressure is also stopping bleeddown.

Just bought a piece of hose to go between pump and fuel bowl hardline to eliminate the one flex to hardline post pump.

 

Can you check KOEO with leaving the key on and see what happens to FP once the 20second time out on the fuel pump relay?

 

Just went and turned key to run let timer run out and you can hear fuel pump relay click off and pressure drops to 0 within 2 seconds.

 

Thank You Kind Sir.

 

Something I just thought of to take in to consideration on what I just tested is I do have a frx installed on mine. So that could effect the drop to 0 I'm seeing. Pretty sure the 2 return holes in the frx are on the back side of the regulator poppet and seat. On the spring side of it. Do you know if yours hekf the 20 psi with the frx installed or did you not check thay until after you took it off.

 

Not until after removal.

Just took another test drive. Dipped down as low as 40lbs, however a thought has just occurred is that I’m down… way down on fuel since I just had the tank out for cleaning. Maybe I’m pulling some air under heavy acceleration. It’s not falling on its face though.

Tomorrow morning I’m going to reinstall the FRx then go and fuel up.

 

Oh. I thought you had replaced that already.

I believe the FRX’s bleed lines are post poppet so it would affect bleed down.

 

Yep. That's why I mentioned it.

 

I had done flex line between the frame rail hard line to fuel bowl hard line. About 18”.

Then I did the entire length from fuel pump to fuel bowl hard line. Almost 4 feet.

 

Sorry, late to the party. And sorry you’re still dealing with this.

I can confirm that it goes to zero within a few seconds after key off or pump time out with a regular FPR. I remember watching this in the past. I can do a re-confirmation if you like.


I would feel more comfortable ruling out pre-pump if pressure drop was confirmed while driving.

I don’t think the drop during running and lack of bleed off are necessarily related to each other. Idle pressure being low could just be FPR set point related while the drop during fuel demand should be related to flow capability.

What FPR kit did you install? The factory plunger has a small hole. I believe this is what allows the bleed down with pump off. I’ve seen other brands (or maybe 6.0 version) not have the small hole.

You changed the entire FPR including the seat correct? Sorry, I could scroll back up and look for it but as you know there is a lot of info to sort through.

While I was catching up on your thread I had a thought but think you’ve already checked it. A possible restriction in flow at the fuel bowl inlet or shortly before there. The bowl was rebuilt with no change and you ran line from pump directly to bowl inlet with no change. This should rule that aspect out. Just throwing it out here in case I misunderstood something.

You also replaced the FRx with a normal style FPR with zero change correct? Should rule out the FPR/FRx.

Pump was replaced and although gummed up you saw no change in pressure drop right? Not even a little bit of difference?

I would probably do a test run with the 5 gallon supply in the bed before doing anything else. If it still drops then you should be able to rule out tank to pump.

 

5 gallon in the bed is such a pita because you have to run the return line there too with no good spot to splice into that line without cutting it.

I also have a canopy/ topper/ shell so length of fuel lines to make that happen is outrageous.

But I get what you’re saying. That’s why I used the 5 gallon on the floor with only the feed line into it. Was hoping to see a pressure increase. None Noted.