I unhooked my feed line on my pump and connected a psi gauge to it and turned the key on to check pressure the pump was putting out I shut it down when it reached 90 psi very quick. Maybe this could help confirm the pump problem.

 

There really isn't a simple way that I can think of. It would involve disconnecting, plugging, and pressurizing the whole system. Are you certain when you replaced your fuel lines at the tank that they snap/clicked firmly into place? I'm quite sure they are a different size and one won't fit the other but if you didn't get them seated right you could be sucking air at the top of the tank.

I'm racking my brain trying to give you all the suggestions I can think of or have run across while doing my fuel stuff but the system is so simple there's not much to suggest to you. All I can think of is obstruction, bad pump, or bad connection. Sorry I can't be more help.......

 

I have though of dropping the tank and rechecking the connections. I'm pretty sure they clicked. I'll see if doing a seal kit on the hfcm will fix the new weird random drop in pressure.

 

Can you give me more details on how to do this?

 

It was two years back so its a little foggy but I was having some fuel issues. If I remember correctly we just disconnected the fuel line that feeds fuel from the hfcm to the secondary filter. Then I took a piece of fuel hose and clamped it on the nipple on the hfcm and put a psi gauge on the other end of the fuel hose and the turned the key on and verified it would build pressure. I feel like I'm forgetting something its been so long.

 

If my current plan of action doesn't resolve the issue I'll try this. Thanks.

 

So everything is put back together.
(new injectors, new-new fuel pump, no restrictions in any lines, fluel pressure regulator upgraded and checked, new seal kit on hfcm, filter cap torqued)

Cycle the key and it struggles to gain pressure. As soon as fuel pump stops pressure very quickly drops. If engine is on it will maintain some fuel pressure but maybe 30psi.

I figure I will have to drop the tank and check everything there since this is a new problem since dropping the tank before.

?Shouldn't the fuel system maintain pressure? It used to.
?Where in the fuel system could a leak cause a drop in pressure?
I'm having a hard time understanding how a loose line at the tank could do this since the tank itself isn't pressurized.

I'm going to get a mechanical fuel pump to double check the results of my in-cab gauge.

Thankfully the low fuel light is on so the tank isn't very heavy.

 

So when I take the gas cap off and put a piece of plastic over it there is no suction. is this a clear indication that I didn't snap the two fuel lines all the way on when reinstalling the tank?

Could an improper seal on the fill tube also have a big impact? How important is it that the tank is pressurized on this truck?

 

Fuel tank is droppped and put back together.

When I did it previously the pickup filter had broken on the top. I fixed it by drilling a hole and sliding it further up the tube. This allowed it to fall off in the tank. The truck was low on fuel and this resulted in the place where the fuel was being sucked up being almost exatly at the fuel level. Essentially the new weird things that were happening was just the truck starving for fuel. New filter installed and after putting more gas into it the weird drops in psi have stopped and the truck is keeping 42 psi.

I figured this was still to low and wondered if my fuel gauge was accurate. Bought a fuel test kit for 42 from pep boys and confirmed that it is accurate (schraeder test port on the extended fuel line from stirctly diesel).

I still wanted to test in other areas and found that Advanced Auto has an amazing fuel pressure testing kit they will loan you. This thing has EVERYTHING. I will easily be able to test after HFCM, and also test just before the fuel bowl. It has all the fitting and attachments. VERY cool. Wish I had known about this a month ago. It would have saved me a couple hundred dollars. I would have been able to test my fuel pump and see theat it was actually working etc etc etc.

I'll post some pictures.

 

Awaiting your test results.

 

That sounds cool Waiting for the Pics

never heard if such a kit

 

This just won't end for ya will it.

First tee in a mechanical gauge, 0-100 psi oil are cheep, I've never trusted elect gauges, lets see what pressure actually is.

Tank is not pressurized, pressure test for leaks is what was suggested.

Pressure will fall when pump times out (20-30 sec KOEO)

PC/ED has 2 tests

1 fuel aeration, remove return line at filter housing & connect a clear line to housing, cycle pump & look for air in fuel.

2 Tee vacuum gauge at HFCM inlet, 6 in hg max.

You in TX now?

 

Yes we are in Fort Worth currently.

1)do you mean at the fuel bowl or at the HFCM
2)do you mean where the fuel comes into the HFCM from tank?

Thanks a bunch

 

Yes to both

 

Ok so I think I found this issue. Now to fix it.

The fuel pressure tester from Advanced Auto although extensive doesn't have the right size fitting for a 6.0. I did get it to do what I needed to do.

First I tested the fuel line leaving the HFCM. I put a piece of hose over the ends and used a hose clamp to tighten it. When I hooked it up I initially got very low pressure until I bled the line. It sputtered until all the air was out then had a nice strong stream. 85 psi.

I wanted to test the line going into the fuel bowl from the hfcm but I couldn't get a good fit. I tested the line going from the bowl to the driver side injectors. When bleeding the line over and over I could never get rid of the bubbles. About 35 psi here.

I pulled the cap off of the secondary fuel filter and kept an eye on it while my wife cycled the pump. Bubbles coming from the supply line. No matter how many times we cycled it I couldn't get the bubbles to stop.

So there appears to be air coming into the line between the metal outlet tube of the HFCM and the inlet into the fuel bowl. Do I just replace the line? Anyone else had this problem. Really wish I had done this right off the bat.