M6950 difficult or won't start

[jlputnam1]

We have an M6950DT with 3000 hours. It's always had some trouble starting - usually does OK with temperatures above 65 degrees and starts without using the glow plugs, but sometimes, even with the warmer temperatures, has to be towed to start - very unhandy when working by myself.

After doing some field work the tractor was parked for a couple of days and now will not start at all (it's about 70 degrees here today). We towed it with the engine turning 1000 rpm and no luck. The starter works OK, seems most likely a fuel issue. We also tried a 225 amp boost charger to ensure enough voltage while the starter was cranking to open the stop solenoid.

The fuel filter has been changed and the bleed procedure followed. The stop solenoid seems OK and was removed to check it's function. Resistance through the solenoid was 52 ohms and the unit seemed to function OK when power was applied. It remains the chief culprit at this point.

We'd appreciate hearing from anyone who has solved a similar problem.

 

[D2Cat]

Did you loosen the fuel lines at the injectors while turning engine over to eliminate air in lines from IP to injectors? I would suggest checking all fuel lines and connections to be sure they are tight. Also, return lines have to be air tight.

 

[fast*st]

Now I don't know an M69 personally but well I just dug into a rough running, slightly hard starting, smoking M70, turns out the valves were really tight on two cyls and slightly tight on the other two. A valve adjustment stopped the smoking and vibrating at idle and across the power range.

tight valves will cause low compression and diesels need all the compression they can get to start. Checking the compression is worth it and when you're in that deep, might as well check the valves.

You might be able to manually engage the glow plugs to help it light off. does it smoke while cranking? white smoke means fuel but no fire.

For doing it my first time it took four hours from start to finish, being careful and adjusting each valve a couple times until it was as good as it could get. to find near TDC or near enough, I'd spin the fan with my finger over the glow plug hole until the air rushed out and then stopped. Clearance spec was printed on the valve cover and interval was every 800 hours

 

[jlputnam1]

We checked the fuel lines and all seem tight. The bleed procedure in my Kubota book includes the fuel filter, two spots on the injector pump and the fuel lines to the injectors. The instructions say to loosen all and then tighten as fuel runs without bubbles, starting with the fuel filter, one on the pump, then the injectors and last the remaining bleed valve on the pump.

We made sure we had fuel in the tank, fuel is clean and without any evidence of water. Cranking and towing produces no smoke at all.

 

[D2Cat]

No smoke indicates no fuel. You say you bled the lines at the injectors. If you got fuel there, injectors are next in line.

I reread you previous post and I think you want to bleed the fuel filter(then shut off that screw) , then the line to the IP (then shut off that screw), THEN loosen the line at the injectors. When you get fuel with no bubbles close one line, then the next until you're through all the lines. Then try to fire it up. Anything come out the exhaust then?

 

[jlputnam1]

Thanks for the suggestion to bleed the injectors after closing off the other bleed points. The Kubota procedure wasn't really clear to me.

I have other field work for a couple of days - setup and seeding with the JD - then I'll get back to the Kubota. The only thing that is meant to stop fuel is the stop solenoid, so I'll check that again - maybe replace it if it isn't too expensive. I did notice that when running the fuel boost pump by hand, there was a difference in the bleed at the injector pump with the key on as compared to the key off - the solenoid seemed to have some effect.

I'll report progress or success when it occurs - this tractor is too handy to sit idle.