My truck has about 190,000 miles and has a slow fuel leak. A while back, I replaced the fuel return hose which had caused a major leak. Any ideas on what component would have a slow leak? It runs fine. I'm guessing that it may be a gasket issue.

 

Rig something up that will allow you to put 3lbs air pressure into the fuel tank [ I used a extra fill cap & put a tire valve through it ] , once you have a few [ 2-3 ] lbs air pressure in the tank , you use a flash lite to fallow the fuel lines to the lift pump [ these have vacuum during normal operation , so they would suck air / not blow fuel ] .
Also check to see if fuel is getting into the crankcase - by way of the LP , also look closely at the lift pump , it has a weep hole , like a water pump , that will leak fuel when the pump leaks internally .

 

About the only fuel leaks I've run into that don't cause hard starting are on the pressure side of the lift pump. This would include the filter and the line from pump and the line to the injection pump.

 

Have you check the fuel pressure yet ?

 

How much fuel have you lost? More than about a quart of #2 should make quite a mess. Just look upstream from the spot/streak. When my return line broke it dumped about 5 gallons of fuel in about as many miles and covered everything with fuel; I mean the whole underside of the truck was wet with fuel.

If you do pressurize the tank don't get carried away with the psi; it's plastic and has a bunch of si's so I'm guessing it wouldn't take much pressure to make it pop.

Good luck, cd

 

I just had to replace my water in fuel sensor. It had a slow fuel drip from the valve on the bottom and only leaked when running.

 

I checked my Cummins shop manual but there's a fixture on the side of the engine just forward of the lift pump that is not illustrated in the manual. I believe it is the fuel heater and may be the source of the problem. A metallic line and rubber line lead out of it. The rubber one goes to the intake port of the lift pump. The leak is slow, unlike that resulting from the return line. A couple of years ago, I had to replace the return line which sprayed fuel all over the place. Does anyone have a diagram of the fuel system lines and the order that the fuel flows in? I'm thinking that the fuel line from the tank goes into the heater, then to the lift pump, then to the fuel/water separator, then to the injection pump. Does the return line go back to the fuel/water separator, or to the fuel tank?

 

Don't over look the electrical connection on the fuel heater it will leak and drive you crazy tiring to find the leak. Email Joe G he hangs out on the TDR site, I understand he has an excellent wright up on the 12v fuel system.

Floyd

 

costal diesel , you have got all if it right .
Find your local Cummins dealer , they will have a much better price than the dodge dealer , also , you can get the fuel heater / pre-filter parts separately , its common for the wire harness to the heater to leak , you may have to insist that it is available separately , it some time but the parts guy at my Cummins dealer did find it .

 

You are correct in your thinking.
The return from the injection pump goes back to the tank but the return from the injectors goes to the filter inlet.

 

I just started it up and saw fuel dripping on top of the lift pump. I checked the fuel drain lever and the fuel-in-water sensor plug on the fuel filter/water separator housing and saw no leaks. After a few minutes, the leak stopped. I'm guessing (hoping) that the leak is at the filter housing/mount junction and due to an old o-ring shrunk by cold weather. I first noticed the leak when I smelled diesel fuel after driving home from work a few days before Thanksgiving. I had been planning on changing the fuel filter anyway. We'll see.

Has anybody removed the fuel heater assembly? I noticed that there is a rubber hose leading from it to the lift pump. Is the intake hose to the fuel heater rubber as well? It looks like a real pain to get to. It's hard enough to see the components as it is.

 

Quite a few folks remove the heater rather than fix it when it leaks. If you take the bottom part off to service the prefilter you'll see how easy it is to remove the heater portion of the unit while leaving the filter intact. Best to have the filter service kit before you start as sometimes the sealing o-ring isn't reusable. Cummins/Fleetguard part number 3845400-S.

The hose from the heater to the lift pump is rubber and can leak though not as frequently as the hoses strapped to the block. The hose is preformed with a 90° and available from the dealer for around $10.
If you use store bought straight hose it takes about 18" to make the bend.

 

I removed mine a few weeks ago. No problems starting or running thus far. You're down in Texas so I'm guessing it doesn't get nearly as cold there as it does up here.

John

 

Thanks to all for the feedback. When I first saw the leak it looked like it was coming from the lift pump. I looked further and could see diesel dripping on top of the lift pump. It turned out to be a leak from the back of the top of the fuel filter housing. It would leak for about a minute after starting the engine and quit. It seems like I didn't tighten it as much as I usually did the last time I changed the filter. Anyhow the leak was resolved when I changed the filter.

 

FYI on my 95 there was an updated fuel line from the filter to the IP. It has a segment of flexible braided line to avoid fatigue and fracture of the line with vibration.
I lost 25gal of fuel just before the 93 toll plaza here because it cracked and leaked fuel. By the time I found out, the whole truck was covered in diesel and the tank ran dry.
A fuel pressure gauge is a good idea