Kubota M6800 Fuel Troubleshoot

[RockChucker30]

Hi guys, My Dad's M6800 is running rough when hot.

850 hours.

What I've done so far:
-New fuel filter
-Empty water separator / clean filter
- Fuel treatment in the tank

Was still doing it after this but I was hearing about it through Dad, so today I worked on it some.

- Took fuel shutoff off, disassembled valve, cleaned with kerosene. (I read this can be the cause. I did not find a screen or mini filter in the shutoff valve like others said they had.)
- Cleaned the water separator bowl & filter again.

I started the tractor and it ran great at 1600-1700 rpm for 29 minutes before I started hearing some fluctuation in rpm. By 34 minutes it was dropping a couple hundred rpm randomly. Then when I tried to increase fuel there was no throttle response. I could lower rpm but not raise rpm? Then I took rpm to idle and then back up and it went fine, then lower slightly and it gets stuck and won't go up.

I thought maybe I was getting vapor lock in the tank or something so I removed the fuel cap. No effect at all.

What I'm thinking now is it's got to either be fuel lift pump or something with the Injector Pump. I watched the fuel in the water separator bowl and couldn't tell any difference in flow even when it was acting up, but I know that's not as good as a fuel pressure gauge - which I don't have.

I'm leaning toward fuel pump, or a screen on the pump being clogged, but I don't know a lot about this tractor and want some opinions before I start throwing parts at it.

Would it be "normal" for a lift pump to go out with 850 hours? I just replaced the lift pump on my 89 ford diesel with 185k and I think it was original....?

Thanks!

 

[thepumpguysc]

To be honest to the point of hurting some feelings>> those lift pumps are junk.. but they keep me in business..
You have to be certain about your fuel quality too.. just because "pops says" he JUST filled up, doesn't really mean he JUST filled up..
That fuel "couldda been" sitting in the shed for MONTHS..??
Go get a 5 gal. container of FRESH fuel & disconnect the tank & run the fuel line straight into your "bucket".. & see how she acts..
Good luck & let us know how you made out.. TPG

 

[RockChucker30]

Update, I replaced the mechanical fuel pump, no effect. These really are a chincy part btw.

So I got 6 feet of fuel line and diverted the feed to the water separator into a 5 gal can of fresh diesel. It ran like a champ for an hour until Dad let it run out of fuel....guess I'll have to bleed the injectors now :laughing:

So this tells me bad fuel or there is a screen or inline filter somewhere in the tank or line between the tank and water separator. My guess is screen or filter that's clogged, because removing the fuel tank cap has no effect on the suction, plus bad fuel should cause it to run rough from the start?

Either way, this is what I was hoping for. It's NOT the injection pump, governor assembly, etc!!!

 

[thepumpguysc]

Way to go.. You saved yourself a big hassle & a few 100.00's in the process..