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I'm looking after a 2008 420 Fourtrax for a volunteer group I'm a member of. It was bought recently as a used machine, it's a 2008 model, so is fuel injected.
It's developed an engine misfire which seems to be getting worse as the weather gets warmer here in the UK.
We use it for hauling a trailer for extarcting logs out of a wood and the cycle is:
5 mins to load, engine switched off.
5 mins transit time to edge of the wood in first gear approx 10 Kph.
5 mins to unload, engine switched off.
5 mins transit time back in to the wood, first gear approx 10 Kph.
The ground is level and muddy, sticky Leicestershire mud!
We use it about once a week and for the first couple of times it didn't misbehave, but after about the third session it began to misfire.
Typically, it's OK when cold, but will star to play up after about an hour, or 3 extraction cycles. It starts to misfire slightly at first, and if the throttle is backed off as much as possible although still maintaining progress it can chug on a little further, perhaps 30 yards or so. However if the throttle is opened up a bit, it just pops and farts and grinds to a halt, however usually keeps ticking over on idle. If it's switched off and left for 5 minutes, it'll start and run for 5 minutes or perhaps a bit further, so can complete another extraction run. If I try to start it too soon, it will fire but not run, waiting a little longer and it always starts and will run and drive OK until the next time. Last saturday it misfired on almost every extraction run.
Originally, I used to let it idle whilst loading and unloading, but it would misfire sooner. Now the engine is always turned off if the wheels are stopped.
One of the guys took the plastic side covers off and that seemed to prevent the misfiring for the rest of the day. I can't say that's repeatable as I forgot to try it on Saturday, when it was last used.
The silencer exhaust exit is sooty and the exhaust smells like it's running a bit rich. I changed the plug as the old one was a bit blackened, however after 3 extraction cycles, the misfire was back.
I've not got any experience with fuel injected engine fault finding so am a bit confused. The smelly exhaust would suggest over fuelling. If it was a carb model I'd clean it, check fuel float level and jets for wear.
The fact that it can be made to run longer by feathering the throttle, but misfires badly if the throttle is opened a bit more suggests a weak spark to me.
I'll do some spark tests next time, however for now, wondered what people think please.
Graham
PS edited to add, as we have no history on this machine, it may well have more than one fault.
It's developed an engine misfire which seems to be getting worse as the weather gets warmer here in the UK.
We use it for hauling a trailer for extarcting logs out of a wood and the cycle is:
5 mins to load, engine switched off.
5 mins transit time to edge of the wood in first gear approx 10 Kph.
5 mins to unload, engine switched off.
5 mins transit time back in to the wood, first gear approx 10 Kph.
The ground is level and muddy, sticky Leicestershire mud!
We use it about once a week and for the first couple of times it didn't misbehave, but after about the third session it began to misfire.
Typically, it's OK when cold, but will star to play up after about an hour, or 3 extraction cycles. It starts to misfire slightly at first, and if the throttle is backed off as much as possible although still maintaining progress it can chug on a little further, perhaps 30 yards or so. However if the throttle is opened up a bit, it just pops and farts and grinds to a halt, however usually keeps ticking over on idle. If it's switched off and left for 5 minutes, it'll start and run for 5 minutes or perhaps a bit further, so can complete another extraction run. If I try to start it too soon, it will fire but not run, waiting a little longer and it always starts and will run and drive OK until the next time. Last saturday it misfired on almost every extraction run.
Originally, I used to let it idle whilst loading and unloading, but it would misfire sooner. Now the engine is always turned off if the wheels are stopped.
One of the guys took the plastic side covers off and that seemed to prevent the misfiring for the rest of the day. I can't say that's repeatable as I forgot to try it on Saturday, when it was last used.
The silencer exhaust exit is sooty and the exhaust smells like it's running a bit rich. I changed the plug as the old one was a bit blackened, however after 3 extraction cycles, the misfire was back.
I've not got any experience with fuel injected engine fault finding so am a bit confused. The smelly exhaust would suggest over fuelling. If it was a carb model I'd clean it, check fuel float level and jets for wear.
The fact that it can be made to run longer by feathering the throttle, but misfires badly if the throttle is opened a bit more suggests a weak spark to me.
I'll do some spark tests next time, however for now, wondered what people think please.
Graham
PS edited to add, as we have no history on this machine, it may well have more than one fault.
