Fuel Issue 2003 Peterbilt

Transportauto · Nov 14, 2023

NightWind said: ↑

I have a 2003 Peterbilt 379. 6NZ CAT.

Symptoms

In the past few weeks I've noticed fuel is coming out of the tanks at the caps.

I changed the caps(new ones) it's coming out of both caps almost like the tanks have some pressure on them.

New fuel tank breather valve and cleaned the hoses to them. and frankly all that seems to have made it worse.

The fuel pressure has been at 80 since I've had the truck but shortly after I got the truck during a regular servicing Cat upgraded something on the fuel system

I have cut offs on both tanks for the returns and service lines.The ball cut off valves haven't been changed since they were installed.

The turbo boost presure runs about 28 (turbo has a waste gate). With the Pittsburg Power turbo the boost was about 32, that turbo had no waste gate.

I have noticed that when I fill up, the passenger side tank holds 50% more fuel than the drivers side.

Any help would be appreciated as I am bumping my head here.
Click to expand...

So arnt the vents there to allow air into the tank as the lever dropps preventing suction and fuel supply loss. Look for bubbles in the fuel. Hard start? Long start? Maybe cups putting compression in the fuel system pressurizeing the tanks?

Last Call · Nov 14, 2023

NightWind said: ↑

Here's the "plan" after talking to the 3 top CAT and Peterbilt Mechanics in my area. I have also received the fuel schematics from Peterbilt/Paccar for my truck so that's helpful as well.

Going to disconnect the return lines, let them empty in 5 gallon buckets. See what side does what. Make any corrections there.

Going to smooth the top edges of the fuel tank necks/openings as there is some slightly irregular/uneven wear on both.

Pray.

Dunno that I have your number....

Click to expand...

That sounds like a good plan. That will give you a good indication of what direction to pursue.
You can call/text the number my friend PM you last week if you wish. I helped him redesign his system on a truck he’s building

NightWind · Nov 14, 2023

Transportauto said: ↑

So arnt the vents there to allow air into the tank as the lever dropps preventing suction and fuel supply loss. Look for bubbles in the fuel. Hard start? Long start? Maybe cups putting compression in the fuel system pressurizeing the tanks?
Click to expand...

Thanks, the truck starts and runs fine. No bubbles in the fuel. We're replacing the fuel T for each side as the passenger side was seeping and the drivers side was damp. Still not done testing everything will provide an update soon. I really appreciate all the ideas and information from everybody.

NightWind · Nov 16, 2023

Latest update. Change the return line and the " Ts" for both sides on the fuel block that seems to have resolved 99% of the fuel cap leaking problem however I'm going to change the suction lines as well and I think that will finish up the problem I hope. However I won't be doing that until after Thanksgiving. I really do appreciate all the help and ideas you folks are great!

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