• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Fuel Gauge detailed results, pump or clog?

Matt Bachand

Matt Bachand

Depends on the 6.5
Messages
5,330
Reaction score
26
Location
Worcester, MA
After driving around for 20 minutes or so my truck runs from perfect to putt putt, and when I cracked my fuel filter bleeder, it hissed and engine died.

I just had my fuel tank replaced a few weeks ago, and just started to re-use my rear tank after almost a year at the same time.

Truck did however run great for one week, filled up both tanks, and then symptoms started.

I suspect crud from the rear tank, possibly clogging my sock.

I'm just not sure how the guage results would back this up before I drop my tank.

Here is my data.

Hooking up to the t-valve, at startup 5.5 psi. Before startuip the pump will pump to 10 then max out.

When my truck started to do putt-putt I went out and hooked up the fuel guage and it went into vacuum about 8psi. That explains the Hiss at the fuel mgr bleeder when I crack it.

Turn off the truck, and jump lift pump via diagnostic connector near fuse box, crack flt mgr, and it fills right up.

Fuel pressure will build to 10 on my guage quickly.

Let it sit there, and it gradually dropped to about 5 or so, after a few minutes of me looking for leaks under truck.

Started it up and watched it. Started back at 5.5 turned on high idle 1300 stayed same.

Then I saw it creep down. In about 15 minutes time it gradually and smoothly crept itself down to 1. I knew from driving it where this pattern was going to lead, so I turned truck off and instantly back on. Jumped up to 3 instantly, then started gradually creeping.

About 5 minutes a psi or so. So not fast, but defanalty consistant creep downward.

Cracked fuel bleeder when it was around 1, still running at this point, and fuel barely broke free.



Now with that information, does that sound like a 5 month old Delco LP dying, or a clog gradually building?

I assume the Injection Pump is making that 8psi of vacuum I read?

Loosening fuel caps lead to no hissing and no change of fuel pressure.
 
Sounds like an identical problem I dealt with a few years back - my in tank sock was plugged.

Take off the LP and blow air back through the line into the tank - let me know how that goes...
 
Just a thought. is it possible that you may have another injector that is not working right. building compression on the injector lines? I would think that if you could blow though the injector that compression could back feed as well. Just a thought. compression is a lot higher than your breath.
 
Nope, it can't feed back past the IP... it's a positive-displacement pump.

I agree with Chris; sounds like plugged socks...
 
Last edited:
It doesn't take much pressure to clear the sock. just a few pounds. Anything more can blow the sock off and that's just not good.
 
Just blow the sock off.....been there done that....been on the road for 250 000 kms without a sock....
 
Here is what I did -

1. Take off the line from the tank to the LP and push the LP back because you will need it in a hurry
2. Leave fuel cap on
3. Blow air into the tank - a few quick blasts in a row
4. Take the blow gun off of the fuel line - fuel should start running out due to the pressure in the tank
5. Quickly reattach the fuel line to the LP
6. Drive the truck and change the filter within a week or so....
 
Mudbath said:
Try same test with fuel cap off. You might have the wrong or a defective fuel cap.
Click to expand...

Same test result with cap off.

Idling after resting for a few hours, started at 5.5 psi, dropped to under 3 in about 30 minutes. Appears to drop faster when driving (more fuel volume)
 
It has been under freezing for a long stretch now, would ice make this do this? Been stuck below freezing the last couple of days. Being 0f at the lowest. Should I add some de-icer additive just to rule that out before I blow the sock off? I always use plenty of de-gel PowerService additive, not sure if that would stop ice slush from clinging to the sock, slowly dragging me down till she gets me!
 
Damned if I know... never bother with the stuff, myself.

It don't get cold in Alberta :)
 
Gonna do the work or are you gonna try to skirt around the dirty part?


LOL...
 
I just read TD's infamous Snot in stockings again.

I must have dead algea all over that sock from the rear tank that just started using again.

I'm gonna blast it backwards and let the filter manager get a workout. I'll be extra careful to remove filter and shop-vac/clean inside of filter mgr housing.

It obvoiusly all gets sucked up within 30 minutes of driving, so maybe i'll test drive it to the parts store and grab another fuel filter, go home and change it out after a little more test driving. That will be the bulk of it I would imagine.
 
Test drive to parts store to stock up on fuel filters, bought 9 feet of hose for fuel pump guage.

Driving around 8 psi, climbing a serious highway hill from stop, faster than I ever drive, it dropped to 5 psi, the second i let off the pedal, back to 8. I'm not a WOT guy with this heavy rig, never have, never will, the heaviest I got on it dropped it to 4psi with instant recovery to 8 the moment I backed off.

Thats one strong LP.

I've seen the vacuum the IP makes when LP is starving, and it was -8psi. IMO any lift pump that is not making around 8 may be starving the IP.

I may try to blow the rear tank sock out too. I think I can get to it.
 
Follow-up

Still 8 psi after installing Turbo Master and test driving it. Set turbo master to go no higher than 9 psi up the steepest hills at the pedal I drive. Had to back spring down to 2.1/4 inches or so, so less boost than the factory recommendations. Don't want to blow her up, just got her running well again :)

All is good in the life of 6.5 diesel for this man. Couldn't be happier with the way she is running now, and nothing like good ol' bonding with the rig in the cold winter.

BTW, very easy to route fuel guage inside hood groove behind hood hinge and into the drivers window. Can even drop the guage in the door compartment, and place it on the steering wheel back when driving.

I need to plumb a permanent one in very soon, for mpg savings (drive it so it doesn't drop pressuer means better mpg for sure), and for troubleshooting/prevention.

Thats another day.

Thanks a ton guys for all your help.
 
Matt, we are all happy that you're back on the road, my friend!

Well done, team!
 
Nice job bro. You stuck it out and fixed your problems and even came up with some good info for the rest of us on the fuel pressure. Nice when you can save some money and fix what you can by yourself and only have someone else do it when your unsure of your own abilities. Again nice job and glad your back to making some money with your truck.
 
You must log in or register to reply here.
Back
Top