J.D. F935, randomly loses power:

[Big Wave D]

Hi all,

Need some help with diagnosing and correcting an issue related to loss of power with the Yanmar diesel that powers this F935.

Mower belongs to a nonprofit organization. The tractor gets used hard with very little TLC. I get the call for help once it totally quits working. So, I once again have just completed a bunch of repairs and standard maintenance on it - to bring it back to proper operating state. All repairs were done, and I was doing some mowing as a test run.

All was fine for over an hour or so of operation in some pretty heavy grass. Then wham - motor just loses power, idles down from full throttle to a high idle, but didn't die. I shut the engine off for closer inspection and prevention of possible, greater damage. Checked for any obvious: Signs of fuel/oil/hydraulic leaks, broken linkage, etc. - nothing.

Issue would seem to me to be fuel related: I checked fuel tank manually to verify what gauge was reading was correct, it was - 3/4 full. I was able to restart tractor with no issue, other than still running rough and unresponsive to any change in throttle position. Moving throttle from Idle, then on up to Full throttle, and any partial setting in-between made no difference. I let the engine run for minute or two while still running roughly, playing with throttle settings the whole time, not sure if that mattered or did anything, but then the engine smoothed out (like all cylinders are firing again), once that happened the throttle would work properly, and full power be available again. Note: I did NOT change the fuel filter when doing all of the other filter changes. Fuel bowl was completely clean, and since I've had issues before with priming - did not want to deal with that fight, this time around.

I've had fuel issues before with this engine. Specifically, it losing its prime. Would this explain the abnormal bouts of pour running? Runs fine - gets some small amount of air into the fuel line - goes into funk - somehow clears air - returns to proper running/power - air once again, somehow gets into fuel line so that process repeats all over again? If not, I'm all ears for any other suggestions for tracking down this problem.


Symptoms, in greater detail:

1. Initially, engine runs strong - all functions normal
2. Power/RPM's just drop, this happens very suddenly
3. Engine never dies - goes into a rough idling state, like only running on 2 of 3 cylinders
4. Throttle setting doesn't matter - Set to wide open, idle, or anywhere in between, engine just continues to idle at same speed
5. While running rough I'd guess idle speed to be around 1,200 RPM's
6. Within a minute or two, it clears itself from its funky running state, and resumes back to acting normal
7. You don't get long before whole process repeats itself, maybe a few minutes or normal operation

Thanks to any and all for taking time to read, and reply to this post.

I bid you all a good day,
Big Wave D

 

[zzvyb6]

Sounds all to familiar. F-935 has 2 fuel tanks. Swithching from 1 to the other didn't help. Only thing that really helped for a while was to fill each diesel tank completely full.

Cause: The fuel pickup lines inside each tank was a hard plastic hose with a crack in each one. Depending on 'things', the pump could pull up enough to run for a while. Filling the tank raises fuel level above the crack. Cutting on a hill made the problem even more strange, but makes sense now.

Solution: Pull out the tank fuel gauge with the attached suction line and replace the brittle plastic line with rubber fuel hose from an autoparts store. If the old line breaks off while pulling it out, fish for it to avoid future skeletons. There is a fuel strainer on the end which should be re-attached to the new fuel line.

All the air mine was pulling also wore out the electric fuel pump, so a new one of those also was necessary. Also from O'Reillys. Get the one with a metal canister and metal inlet and outlet lines.

Watch for the need for new glow plugs, too. Cold weather aids, but low cost from eBay sellers.

 

[hosspuller]

Agree with ZZ ... I had the same issue. The plastic line can be purchased from ANY Deere dealer... Farm, Construction or L&G.

The part number for the bulk hose is : PMK2812-0406 Buy a couple of feet and cut to length

 

[pmsmechanic]

So I had almost the roughly the same problem. I never ran out of power while mowing but if I ran out of fuel on one tank it was a pain to get primed.

Most of my issues were with starting cold. If the mower sat for more than a week I would need to bleed the fuel otherwise it wouldn't start. One time while bleeding I over tightened the bleed screw on the fuel filter stripping the threads. I looked the filter head over looking for ways to repair the threads but in the end I decided to just buy a new filter housing from John Deere $70. Once it was installed my fuel priming issues were over. There must have been a small leak in the filter housing somewhere.

I had read about the tank hose issues and am going to replace those at some point in time also but for now my problem is solved.

Just adding this so that if changing the suction hoses doesn't solve the problem, the filter head is another place to look

 

[muddywaters80]

Hi, apologies for commenting on such an old thread but I am having these exact issues. I have bought some new rubber fuel line, Can someone tell me how to remove the tank fuel gauge please?

Thanks ion advance