Stamey

A friend's 96 3500, with 206K on it, will start, after sitting overnight, and run for about 20 seconds then begin running rough and cut off. Getting it restarted requires, get this, pushing the accelerator down. I never thought that would help an air in the system problem, but it does start, while giving it fuel, and runs rough, then you have to keep giving it fuel until it smoothes out.
When you cut if off during the day and restart it everything is fine, which suggests a slow air leak in the fuel system.

I did a search on here the other night and found the likely culprit to be air leaking into the fuel system, as I suspected, and the likely suspects, being the fuel heater, cracked hoses, etc.
For troubleshooting I pressurized the fuel tank, by rag and an air hose, to see if I could see where the leak is. No luck here, I increased the air pressure as far as I dared, with a friend holding it and me looking for the leak, under the hood and under the truck. I can't se any hose problems, as none seem to be cracked or dry-rotting.
Everything I can see is dry as a bone, including the filter, hoses, lines and fuel heater, and I need to know what to look for next, or how to proceed with finding this leak.

Thanks for any advice,
Chris

infidel

Next step would be to check fuel pressure or just replace the overflow valve.
Instructions> http://dodgeram.info/tsb/1996/14-07-96.htm

vzdude

^ X2 !! Sounds like the likely culprit.

kawi600

Or sucking air into the lines somehow. You can patch a clear fuel filter into a line someplace temporarily to spot air.

Stamey

Any suggestions for how to check fuel pressure? The only thing I can think of, not having the "special tools", is to drill and tap a banjo bolt that I can connect my fuel pressure gauge to.
Where should I put the clear fuel filter? The only place I can see that looks like I can tap into is the elbow between the fuel pump and the fuel heater, besides the lines bakc by the bell housing, which I probably would be able to see anyway. Did I miss a good spot?

Thanks,
Chris

infidel

That's exactly what you need to do.
Instructions> https://www.dieseltruckresource.com/...41&postcount=9

vzdude

There are 2 plugs on the top of the fuel filter housing that you can remove and put an 1/8" NPT fitting in to read pressure. One is psi in ans the other is psi out. 96 does have the aluminum housing right? One nut in the middle to remove filter? That should be right.

infidel

Only on 24 valves, 12s have no such provision.

Stamey

Thanks Bill. This should help. I will start gathering parts this evening.
Someone else said I should check the shut-off solenoid. I notice when I turn the key on, it goes to some position (doing this alone), and has more travel left. If I pull it up to the farthest position it will go it seems to lock in place all the way up (with the key in run position).
My understanding of the solenoid is that when you turn the key on it goes to "run" position, and when you start the truck it goes to the "start" position, which I guess is further opening than "run". If this is the case, why would it stay in the position I pull it up to, as far as it will go, when the key is in run position?
Neither position has made any difference in the way it runs yet. I was unable to get it to cut off 2 days ago, as I had it parked so that the tank was slightly uphill of the engine, whereas it's normally parked with the tank slightly downhill. It just ran rough for a few seconds and smoothed out.

I parked it on a hill, with the tank lower than the engine and it will likely cut off after about 20 seconds when cold-started.
It only has about 1/8 of a tank of fuel. will that make any difference here?

Thanks,
Chris

vzdude

I sometimes have been known to have these "brain farts" that cause posts like that!

infidel

Chris, the solenoid's two positions are more like lift and hold. It takes a lot of juice to lift the shutdown, this portion of the coil is only energized while cranking. Only the hold portion is energized in the run position.
Both positions lift the solenoid to the same height. The adjustment for this doesn't change unless someone messes with it but the solenoid plunger can get full of gunk especially if the boot is torn and restrict full movement.
Remove the solenoid, clean it and lightly coat the shaft with silicone grease.

If it doesn't act up with a full tank the problem could be a hole in the fuel tank module's pickup tube. There are some sharp tipped self tapping screws that hold the unit together that are well known to wear holes in the hose.

I've also found that leaking metal lines on top of the bell housing can suck air and make for a hard start with a low tank. There is no way to see these lines, you have to feel for wetness. Even if fuel never drips to the ground it's enough to cause hard starting.

Stamey

Dang, what a pain. I suppose I will have to pull the lines off the bell housing and see if I can get them low enough to inspect, or remove them and pump them up with air.
The feel for wetness won't work here as they are wet with oil. I was hoping that pressurizing the tank would push enough fuel out that I could see more wetness or perhaps a drip, that I would be able to track down despite the oil. I might be stuck cleaning the underside of this thing to find this leak.
The oil leak has been another hard one. He keeps telling me it's leaking oil like crazy (I was thinking KDP), but every time I get the truck I can find no real leak, just areas that are a little wet with oil, but not enough that it drips on the ground, so I'm still trying to track that one down also.

Chris

markm4

Nice write-up on the guage install Infidel! I did something similar in my old Mercedes diesel using an oil pressure gauge, but not as neat as your install. Am I reading it right that the lift pump supplys 40 psi to the IP in these trucks? In my old "similar technology" Mercedes 5cyl, the lift pump only gave like 7psi, and with larger supply tubing from the tank, The Mercedes dosn't seem to need a lift pump at all. Similar inline injector pump, or so I thoght?

P.S. don't forget to post how you guys resolve this, becaue I have THIS EXACT SAME ISSUE on my 1997. Starts and dies after about 20 seconds and only in the morning, restart with a little throtle, and it is good to go. I'd put my money on an air leak too.


Mark, in NJ, and yes I am very new here,...
Hello, by the way

infidel

The 12 valve lift pump is very strong, I've seen them put out in excess of 100psi if the return line is blocked.
What keeps the pressure down to the factory recommended 35psi max is the overflow valve, which is nothing more than a relief valve to the tank return.
More is not better, fuel pressure in excess of 45psi can blow out expensive to fix internal injection pump seals and even split open the fuel filter.

markm4

Thanks for the info on the fuel system.

This morning I just drove it a little faster than usual for the first 20 seconds and it didnt happen.