mooktank

I've noticed in the morning my truck will idle at 15psi but quickly go to zero if there is any load on it. After driving 20 mins (most of the time at zero) it will start to maintain around 4psi cruising at 40mph. Later in the day it can cruise at 15psi after it warms up and the truck is warmed up.

Is this a sign of water in the fuel or a bad fuel filter? I feel bad driving the truck cold because im sure the fuel is really viscous and having trouble being pumped. Anyone have any insight into this?

JD730

Sounds like its having trouble pushing fuel through the filter, I'd toss a new one on there and throw some white bottle power service in the tank.

mooktank

I should have mentioned the filter is fairly new but I have one lying around so I may just change it. If it's not bad it's a waste of 10 bucks tho.

wannadiesel

Might it be a problem with your pressure gauge setup?

How cold is it where you are?

Ace

I noticed a 2-3psi cold pressure drop with the diaphragm pump a couple months ago. It would slowly come back up after warmup. But what you're seeing sounds like too much to be the explained away by cold alone.

mooktank

I wouldn't expect there to be a problem with my gauge setup since it seems like it works fine once up to temp. I have a feeling it could be the filter or maybe the fuel getting a little thick. I'm gonna throw some fuel additive in the tank and see how it goes.

wrm

if you replace your filter and use a bottle of power service 911 in tank that will tell you for sure if it is filter or fuel related good luck.

wldcat

Our winter driving frequently has temps 30 to 50 below, and at first I had a low pressure problem as well. Mine was fixed by changing the anti-freeze mixture I was using on my gauge. I also run the clean diesl (white bottle additive) which stops gelling.

ofcmarc

Sounds like you might be starting to gell. How cold is it? A post filter pressure gauge will read 0 psi if the filter gells and quits flowing fuel. Change your filter and add some more anti-gell of your choice.

mooktank

It's just barely below freezing these days actually.

wannadiesel

Shouldn't be gelling then.

mooktank

I replaced the filter today. I even cut it in half to check if anything was clogging and it didn't look like it.

It seems like it's doing it more randomly now. More prominent the colder it is.

I have a piston lift pump in it that's fairly new. What are the odds of it bein a little shaky?

wannadiesel

Not likely, but possible. How's the tank vented?

mooktank

The tank has a rollover vent which just goes to the atmosphere.

Tonight driving around it will go down to nothing if I stab the throttle. This is really getting on my nerves because I feel like I'm going to kill my IP.

Is it possible my fuel lines are too small? I have 3/8 from tank to lift pump then stock lines from there on.

I'm going to try blowing out the feed line it's possible something got in there since I do have 2 blocks of safety foam in my fuel cell to keep it from sloshing.

It's just so weird it seems like more of a volume thing than a pressure thing. It's definitely related to temperature and throttle position. ARG.

wannadiesel

3/8" should be plenty. It's diesel rated hose and stiff enough that it's not sucking shut, right?