6.5 turbo diesel - fuel starvation

[mystrydiesel]

I have a 1994 6.5 turbo diesel which I can start cold & it will sit there and run fine at idle for hours.When I start putting the truck under a load it stalls & is hard to start ( if I open the drain or air bleed valve - I get no fuel). I f I let the truck sit for hours (overnite) it will start right up and idle for hours again. I have tryed several new lift pumps - replaced sendingunit in tank - new lines tank to LP to fuel filter housiong - to injection pump..several new filters

? if there may some sort of problem in the filter housing ???when I changed the filter - the spring in the center had some rust on it - I removed housing - cleaned out - replaced ..

[DennisG01]

Is the lift pump actually running? If you listen closely, you can hear it when you turn the key to "run" while waiting for the glow plugs. With a helper turning the key, or once the engine is started, you could also check for 12v at the lift pump's plug.

[mystrydiesel]

Yes. I actually wired a switch directly to lp

[greatwhite]

Well, it's a fuel problem if you're not getting fuel from the water drain.

IIRC, the water drain is prior to passing through the filter (the "T" valve at the front of the engine).

This would seem to indicate Filter manager back as the problem.

The thing is; there's not a whole lot back there.

Lines, lift pump, pickup, tank.

You seem to have eliminated lift pump and pickup as the problem.

That leaves lines and tank.

Look for rusted hard lines. If air is getting into the lines through rusty lines and fittings it can cause running problems.

You have repaced the pickup, but make sure that you don't have the fuel strainer/sock from a gass truck. They are reported to be more restrictive than diesel ones and could cause fuel starvation issues under load if this is true.

Last thing I can think of is the fuel cap itself. If it's not a diesel one, it may not be venting properly and allowing air into the tank. Gas fuel caps are more restrictive and they need to keep a higher vacuum on the tank. Diesel caps allow more air into the tank so the lift pump can pull the fuel out easier. Although, that seems a long shot with NO fuel coming out (vice weak flow) of the drain line when opened.

I really would look at that lift pump again. that sounds like a likely culprit given your description.

My sympathies to you. This kind of thing can be really frustrating to hunt down....

[DennisG01]

I'm going to suggest something, although I've never done it and have never delved this far into my engine to tell you exactly how to do it. But, could there be a restriction (dirt or crud) between the LP and the filter? How about removing whatever line comes to the filter (along with removing the upstream side of the lift pump) and blowing air back through? Would that be a logical thing to try?

Same general line if thinking... While the upstream side of the LP is disconnected, use your switch (which eventually you'll want to disable for safety reasons) and power up the LP. Collect the diesel (maybe use an appropriately sized rubber hose to help divert the flow) in a bucket while observing how fast the diesel pees out if the LP.

[hatzie55]

I have a 1994 6.5 turbo diesel which I can start cold & it will sit there and run fine at idle for hours.When I start putting the truck under a load it stalls & is hard to start ( if I open the drain or air bleed valve - I get no fuel). I f I let the truck sit for hours (overnite) it will start right up and idle for hours again. I have tryed several new lift pumps - replaced sendingunit in tank - new lines tank to LP to fuel filter housiong - to injection pump..several new filters

? if there may some sort of problem in the filter housing ???when I changed the filter - the spring in the center had some rust on it - I removed housing - cleaned out - replaced ..

I don't see the oil pressure switch on the list of parts. If the fuel pump cutoff half of it doesn't switch then the fuel lift pump won't run.

[JTodd]

I actually spent a great deal of time tracking down a similar problem. Here is what you should do.

1. Confirm the LP is pumping.
2. Remove the LP and attach a 3/8 ID rubber line to the line going to the tank (it is a really tight fit, but you need it on tight to make it air tight), remove the fuel tank filler cap and flow air back into the tank. If you do this by mouth, you should be able to tell if it is restricted or not. You can also suck and siphon fuel this way to see if it flows.
3. Remove the fuel filter, and attach the 3/8 ID rubber line to the line going to the FFM. Blow to see if there is any restriction.

There are really only a couple areas to look for that would keep the FFM from filling - which is the exact problem I had. Either the LP is not pumping, the fuel tank sock is clogged or there is a kink in a rubber line. In my case, it was the rubber line between the hard line and the FFM. I went after the tank sock, but should have waited until I had looked everywhere else.

Here is the link to my issue. http://www.thedieselpageforums.com/tdpforum/showthread.php?t=40339&page=5