Ford 550 Diesel won't start when warm...

I have a Ford 550 TLB that I've done a lot of work to, but have a recent problem I can't figure out.

The machine starts fine first thing in the morning when the engine is cold regardless of the outside temperature.

The problem arises when I shut the unit down and try to restart it. When the engine is warm it will not start for anything! I have to use starting fluid to get it to start and sometimes I have to keep it running on starting fluid and get the rpms revved up then it takes off like a rocket with the throttle wide open. Here's what I've checked:

The engine gets plenty of fuel and the injector pump works just fine. The injectors appear to be working fine - once running it has plenty of power, doesn't smoke, and at top rpm's it doesn't shutter at all. The motor was completely rebuilt about 250 hours ago. There is plenty of oil and pressure. The cylinders all have really good compression. And lastly the air intake is just fine.

The problem has me baffled. I was thinking a sticking valve, or an injector that is clogged, but nothing seems to fit other criteria for them having issues. Any help is always appreciated!

thahn1608 said:

The engine gets plenty of fuel and the injector pump works just fine.

Click to expand...

When it's warmed up and cranking but not starting, do you get a white fuel mist/fog out of the exhaust?

Makes no sense to me, but that's a start in the right direction. If no mist, does this thing have a electric fuel solenoid (instead of a fuel shut off rod) and what is the resistance (ohms) when it's hot vs cold?

It is a mechanical unit. I do not get anything out of the exhaust except for the typical rain cap jumping. It cranks as if it isn't getting any fuel to any cylinders even though it is. Not one cylinder even tries to fire. Typically I don't get any smoke out of the stack at any time - it's practically a brand new engine.

No smoke/fog=no fuel to the cylinder. A solenoid coil being weak when it's warm is a typical failure, if you have a wire going to your pump, not a shut off rod. If you have a shut off rod, then it's time to take the cover off the pump, or get a second opinion.

I dont know anything about this tractor, but a diesel engine is a diesel if I was to start I would get the tractor warm to where it dont start then crack the fuel line to see if it is getting fuel(more then likly not if it will start with start fluid) if not look for leaks from the lines if not change the fuel filter then look at the fuel shut off and then to the relays if there are any in yours. I am sure some of the fine people that know more about this tractor will answer your questions.

Thanks. I've replaced all the fuel lines from the injector pump to the injectors since they all had a slight leak. I have loosened the injector lines at the injectors to see if fuel is getting through. There are always drops coming out of the lines while it is cranking and stops when it's not... Since it's an older unit (think bicentenial year) the cranking speed isn't terribly fast so it's never really had any mist coming from the stack.

It seems whenever I crack a line (for bleeding) I get a pretty good spray, definitely more than drops.

If the machine isn't puffing smoke when it's cranking, it's not getting fuel to the cylinders. When you shut the machine down, do you simply turn off the key or must you pull a knob?

Key: As mentioned, possible problem with the fuel solenoid or connection to it.

Knob: If it's a cable operated shut off, there's a possibility the cable is hanging up and not fully releasing. You'll have to physically verify it's movement at the injector pump. Make sure the shut down lever is fully returning to the run position.

I think Steve's wins this round..
Try disconnecting the S/O rod entirely from the lever..Hold the throttle WIDE OPEN/full throttle..
and give the s/off lever a couple of quick flips with your fingers..back and forth afew times..NOW try to start it.
Sounds like a sticking metering valve.

My tractor did the same thing a while ago. It started somehow (it required good cranking speed) when it was cold, but as soon as it got a little warmer, it wouldn't start at all. The problem was solved when I changed the hydraulic head of the injection pump. Now it starts in all conditions.
So, if this problem diddn't appeared just right now, do a test and cool down the hydraulic head of the pump when engine is warm. If it starts, with the head cooled, then it's clear that there is your fault.

Thanks guys. It is a mechanical unit and yes, I always verify that the fuel shut off lever is completely disengaged before I start it (The cable doesn't fully retract the lever so I always have to check it).

Marius: That's something I hadn't considered. I'll check it out this morning when I'm working the machine. It's a piece of equipment I use several times a week and usually for multiple hours at a time. Looks like I need to do some investigating on the pump...

hey, my older 4500 did the same thing. had the pump rebuilt and woila...problem solved.

Thanks guys! I'm going to do some more testing, but it appears that a pump rebuild is in my future. It's the last major item on the tractor that hasn't been rebuilt...