Ford 3930 Losing power

[jlanglois]

My Ford 3930 has started losing RPM's. When I pull the throttle lever to full speed I get 1,500 to 1,700 rpms. Full speed used to be 2,200.
Is there a chance the throttle cable slipped or is it more likely that it's crud in the fuel lines?

Also, how much rpm diminishment should I expect when using my Wood's 6 foot bush mower?

Thanks.

 

[fishheadbob]

Start with whichever looks esiest, probably the cable, and go from there.
3930s had a lot of balls, a 6 foot bush mower shouldn't be a problem.

 

[Harry in Ky]

There is no cable on a 3930. It's all rods. Stand next to the tractor, pull the throttle lever all the way and look at the injection pump. Is the lever on top of the pump all the way against the stop screw? Is the fuel shut off lever all the way forward? If yes on both counts, it's not a linkage problem, more likely a fuel related problem

 

[jlanglois]

Thank you, Harry.
That eliminates one variable. When the PTO is not engaged, I can get the RPM's up to about 1,700 1900. Sometimes they get to 2,200, which I consider full speed.
It is the variation in speed that leads me to think there may be some crud in the fuel lines or air leaking in.
Since this thing has fuel injectors, how do I clean and test them to see if that's the issue?
Thanks

 

[Harry in Ky]

YOU don't clean fuel injectors. That's not a homeowner friendly operation. You can however, change the fuel filter(s) and see what you find there. Have you ever done that? Your description of the symptoms leads me in that direction. That too, can be a headache if not done properly.

 

[jlanglois]

It's taken on a new behavior that I believe is fuel related. When I first crank it, I can get up to 2,000 RPM. Under load that drops to about 1,700. As I move down the field, rpm's drop to about 500. However, if I shut it down and let it rest for 30 seconds, it cranks again and will run at 2,000 rpm for awhile.

To me that sounds like a fuel reservoir of some description is getting replenished. I have a new fuel filter on it. Is there a bleeding technique that would help me diagnose this?

Thanks.

 

[Harry in Ky]

At this point my next guess would be a problem getting fuel out of the tank fast enough. A rather common problem, and although it's a bit messy, it's not all that difficult. It would involve removing, inspecting, cleaning, and re installing the fuel tap under the tank. It looks like this. Sometimes the screen will be just plugged up with debris collected over time. Sometimes it's off completely and junk gets into the fitting itself slowing down the fuel supply.

Ford Tractor Fuel Tank Shut-Off Valve with Filter Screen

Solve your leaking fuel valve issues with our durable and compatible Ford Tractor Fuel Tank Shut-Off Valve with Filter Screen. Perfect for 3-cylinder engines.

www.brokentractor.com

 

[blehmann]

My 3930 did the same thing about a month ago. I had just finished shredding 15 acres of wheat and turned quickly. There was a hump that I went over that jolted the tractor a bit. I immediately sensed a loss of power. My first impression was that the jolt had stirred up some sediment in the sediment bowl and let it pass over to the fuel filter. I went to the dealer and got a new filter and new o rings for the sediment bowl. When I got the filter off I could see sediment in the bottom cap of that system and then when I got the sedimentor opened up I could see that it likely hadn't been serviced in years. After cleaning and reassembling I opened the air bleed bolt and opened the fuel valve to purge air from that part of the system. When no more bubbles came out with the fuel, I tightened the bleed bolt. The tractor started and ran for a couple of seconds so I then started working my way along the fuel line, bleeding air at each fitting until the tractor would start and run. It is not the best system that I've seen. The three o rings in the sedimentor have to be perfectly aligned and tensioned correctly or there will be a seepage. It took me three attempts to get that part right. There are three o rings. The two that match are for the glass cylinder sealing and the slightly larger one is for the top of the steel ring fitting above the glass bowl.