M4800 SU Smoking and Knocking

[Georgia boy]

New here. I have a 2005 M4800 SU 2WD, and in the last three years it has started smelling of raw fuel and eventually, when mowing and getting into heavy grass, it will start smoking and knocking. I have added fuel injector cleaner, changed fuel filter, drained fuel with no luck. I have had a Kubota dealer come and pick it up, they kept it for a week and found nothing wrong. It actually cleared itself up fort a whole season but the next season it started smelling of raw fuel and eventually started smoking and knocking again. The knock sounds like preignition to me, and the raw fuel leads me to think it is a fuel issue. The last thing I did was replace the small fuel pump next to the injector pump but no luck. It actually started knocking and smoking not long after I put the fuel filter on much sooner that it has before. I am getting some new rubber fuel hose to put on it for my next attempt. Should have gotten that with the fuel filter but didn't . Hoping I don't have to get into the injectors but it may be where I'm headed. That seems expensive and a pain to do or expensive to get someone else to do. Would like to hear someone else's ideas on what may be wrong. Any help is appreciated.

 

[lugbolt]

check compression first. Wouldn't be a bad idea to do a valve adjustment while you're at it, assuming it's got some hours on it. If compression is ok, your air intake is not restricted or sucking the hose shut, filter's clean, and it is not sucking oil into the engine, then you could send the pump and injectors out for inspection. But based on my own experience, Kubota pumps and injectors are not often failure points. I found more "other" stuff wrong, on equipment that may have been at other shops and those shops deemed inectors 'bad'. Bad fuel, oil being pulled into the intake, poor compression, etc.

 

[cthomas]

Did the dealer remove the injectors and check flow and popit pressures?

 

[North Idaho Wolfman]

My choice is you have a bad injectors or several!
Pull them and look at them, bet one or more will be wet or black or both.

 

[Georgia boy]

check compression first. Wouldn't be a bad idea to do a valve adjustment while you're at it, assuming it's got some hours on it. If compression is ok, your air intake is not restricted or sucking the hose shut, filter's clean, and it is not sucking oil into the engine, then you could send the pump and injectors out for inspection. But based on my own experience, Kubota pumps and injectors are not often failure points. I found more "other" stuff wrong, on equipment that may have been at other shops and those shops deemed inectors 'bad'. Bad fuel, oil being pulled into the intake, poor compression, etc.

Thanks for the reply. Forgot to mention I have changed the air filters recently with no luck. I'd have to find someone to help me with a compression check or take it back to the dealer. Last night I did play with the bleeder valve for the fuel system and thought I was getting somewhere. In the past I have changed the fuel filter and recently changed the fuel pump and it started back up without using the bleed valve. I'm not a diesel mechanic and just found out about the bleeder valve on this tractor. Will still be changing the rubber fuel lines soon to see if that helps.

 

[Georgia boy]

Did the dealer remove the injectors and check flow and popit pressures?

Thanks for the reply. When the dealer had it of course if ran like a champ and never did any smoking or knocking. They claimed they even put it under a load. So no they did not remove the injectors. I took a few weeks after I got it back from them for it to start acting up again. It very well may be the injectors but I'm just trying the easy to get to things first.

 

[Georgia boy]

My choice is you have a bad injectors or several!
Pull them and look at them, bet one or more will be wet or black or both.

Thanks. I'm going to do a few more simple things but you are probably correct about the injectors.

 

[North Idaho Wolfman]

Curious this is a M4800 or a M4900 as you have listed as equipment owned?

 

[Georgia boy]

Curious this is a M4800 or a M4900 as you have listed as equipment owned?

M4800

 

[North Idaho Wolfman]

M4800

Do you also have a M4900 or was that a typo?

 

[Georgia boy]

Do you also have a M4900 or was that a typo?

That would be a typo. Just have the M4800

 

[North Idaho Wolfman]

Fixed it for ya!

 

[Georgia boy]

Fixed it for ya!

Thanks

 

[Grandad4]

Just a non-expert's guess here, but could there be crud in the fuel tank? When they hauled it off to the dealer, maybe it stirred things up enough so any blockage was temporarily clear of the fuel line intake, and it ran Ok for a little while. Seems to me it would make sense to verify that there is good flow from the tank to the fuel filter before getting into more complex issues.

 

[Georgia boy]

Just a non-expert's guess here, but could there be crud in the fuel tank? When they hauled it off to the dealer, maybe it stirred things up enough so any blockage was temporarily clear of the fuel line intake, and it ran Ok for a little while. Seems to me it would make sense to verify that there is good flow from the tank to the fuel filter before getting into more complex issues.

Thanks. I have drained the tank at one point and put fresh fuel in it with no luck, but you are right, there could be something in the fuel lines moving around. It could probably use all new fuel lines anyway. Working on it.

 

[cthomas]

You could mount a boat tank to the ROP's and hook that up to the injection pump, at 5 feet of drop that would give you about 2 PSI of fuel pressure to the injection pump. It would eliminate the fuel delivery system. Just make sure that the tank is clean and empty.


Too bad you didn't have both tractors, you could just swap injectors.......

 

[North Idaho Wolfman]

Smoking and knocking is not a symptom of lack of fuel, its a symptom of too much uncontrolled fuel being injected into the engine.
Or fuel being injected at the wrong time.
The chances of it being a bad injector are real high, the chances of it being a bad injection pump is pretty low.

 

[Georgia boy]

Smoking and knocking is not a symptom of lack of fuel, its a symptom of too much uncontrolled fuel being injected into the engine.
Or fuel being injected at the wrong time.
The chances of it being a bad injector are real high, the chances of it being a bad injection pump is pretty low.

I'll let yall know when the injectors come out. It may be next month when it cools down some. It's so hot here now it's hard to breath outside.

 

[Georgia boy]

Well I took the injectors out of the M4800 and sent them off to an injector shop over in Augusta. A few days later they let me know that one of them was bad. They said injector body was bad. They cleaned and checked the rest and replaced the bad one. I put them back in yesterday and got it cranked. I have mowed with it for a couple of hours now and no smoking or knocking and it runs really good. Thanks for all the advise and knowledge. I'll update if any more problems come up.

 

[BAP]

Good to hear. Next time, I would find a different Kubota dealer to take it to for service work. The dealer should have pulled the injectors and checked knowing the symptoms that you were having.