6415 with wandering rpm

I have a 2004 6415 which varies rpm. The tractor since new, and now with only 260 hrs, has varied rpms. At first it was using the governor when mowing. RPMs could drop to 1200 from 2200. Now it even does it at idle. JD said bad fuel and I have been through 3 sets of filters, then they said minute holes in bad fuel hoses. They are at a loss to explain. Does anyone know?

Welcome Timberwalker.

I'm a little out of my area with big Deeres, and yours is big. Like 85 HP, turbo 4 cylinder big.

Only once did we work on something (smaller) that had similar problems...and the short story was a poor seal in the very large pre-air filter seal. Evidently that twin seal inside the can, when not properly seated...and along with the vortex generator (the funny plastic propeller looking thingy) on the filter itself are enough to drive experienced mechanics in circles.

Could it be something like that??

Good luck, hang in there, as there are better JD guys who may be able to help.

Mark

Sure sounds like it's sucking air somewhere.
I have a 6420 and it doesn't vary rpm (thankfully).
Hope you can get it figured out - they are too nice of a tractor (re:$$$) to have problems with!

Welcome to NTT TW.

Good description of the problem. I have the same issue on my new to me 20 year old houseboat. I run two 7.4L (454) crusaders and I can't count on either tach to be correct. The engine rpm will be constant but the tach can be all over the place. Once in awhile they are right, but more often than not they are jumping around.
I now wonder if air is the issue on these also.

Good luck getting yours figured out. Please post back once you do. Maybe, just maybe it will give me a clue as to what the issue is on my boat.

Doc said:

Welcome to NTT TW.

The engine rpm will be constant but the tach can be all over the place. Once in awhile they are right, but more often than not they are jumping around.
I now wonder if air is the issue on these also.

Click to expand...

Doc,

My guess would be electrical in your situation. If the engines run a constant rpm but the tachs are all over the place, either the tach, the wire, or the pickup is probably bad. After 20 years in a marine environment it would not be surprising for an electronic instrument to have lived out it's useful life.

Oh yeah...John Deere

I would guess that it is sucking air somewhere too. Does it give out any smoke when the revs vary?

If fuel hoses are now ok and the electric transfer pump in the tank is putting out a good flow of fuel, I would suspect a bad injection pump. It sounds like the governor is out of kilter. You need to get your dealer to resolve this before the tractor gets any older. If you have documentation of prior problems, you should get it covered even though it over 2 years old.

Does it ever rev UP? That may indicate a governor issue.

By RPM's dropping only, I'm inclined to go with the crowd on this one. Sucking air into the fuel system. Check for good seal around fuel filter as a starting point.

I've got an '07 6430 that's been trouble free so far, but I've gone through simular problems with several older tractors, most recently my Massey Ferguson 150. It was drawing air through a leaky diaphram on the primary fuel pump. It would be running fine, then drop 500 to 1000 rpm, level off, then sometimes return to previous rpm's OR just quit altogether. A $12 rebuild kit solved the problem.

IMHO, the Deere service guys are CLOSE when they say a fuel problem. I'd say it's a fuel SYSTEM problem.

Not sure what type fuel pump this has, but if it's a diaphram type, it could very well be that one or both of the check valves have come loose in their seat. Had that happen maybe 3 or 4 times over the years. BTW, our symptoms were identical to yours, down to finally getting to idle variances.

Don't forget that little radiator that the fuel return goes through after leaving the injectors. Ours developed a leak and it took forever to figure that one out. I like our 6415, but the fuel system is quite problematic.

wow, nothing like the new guy waking up a three year old thread - sorry guys...