John Deere 850 slight miss sound

[stinson89]

I just recently bought a John Deere 850 for a super cheap price compared to what the market is in my area. Everything seems to work as it should and it seems pretty clean. The only issue I’m having with it is it seems to have a slight miss to it around 2,000rpm not sure what it could be I’m going to try running some additive through it and see if it will straighten out but not sure what it could be I’m definitely thinking something fuel related. Anyone have any ideas thanks

 

[USMC43]

You could have a plugged filter, worn pump, a miss timed pump, a bad injector, valve lash out of spec

Does it do it both under load and high idle?

 

[stinson89]

I have been able to put it under a load yet just noticed it around high idle

 

[USMC43]

I would check the valve lash and change the fuel filter first. Maybe even pump out the old diesel if it’s been setting for a while and putting fresh diesel in. Do you have countrymark diesel where your at in Kentucky?

If it doesn’t clear up check the timing and if that doesn’t do it remove the injectors and have a injector/pump shop test them.

 

[dodge man]

I agree change the fuel filter. I don’t know if that model has one or two fuel filters.

 

[stinson89]

Ok I will try to track down a fuel filter after work. Question will it have to be re primed after changing the filter and if so what’s the best way to go about it

 

[USMC43]

Yes. If I remember correctly there are two phillips screws on the top side of the fuel filter head. Put throttle 3/4 and loosen left screw until air stops coming out then repeat with the right screw.

Sometimes you need to loosen the screw on the fuel pump in front of the three injection lines and bleed it. Very occasionally and just for good measure since you are having issues, crack the injector lines (at the injector) one at a time and make sure they are bleed.