M4800 just started loosing power under load

[huntersprings]

I have a M4800 with 500 hours that has just started loosing power under any load. This can be pulling a box, mowing or climbing a hill. The tractor dies if I don't let up. Idles and moves on flat ground without a miss. I am no mechanic by any means but prefer to do as much as I can before turning it over to the dealership.
The RPMs decrease despite throttle and there is little or no smoke. The air and fuel filter were changed two months ago. The fuel filter cup stays full while tractor is loosing power.
Does anybody know of a reference link with a diagram of the parts on the 4800s engine. I'm not sure how to drain the tank except for pulling the line feeding the fuel filter. Also, if I'm looking at the right thing, the injectors are behind the manifold under the fuel tank and look difficult to get to.
Any suggestions where to start first or a reference manual would be much appreciated.

 

[North Idaho Wolfman]

Sounds like you have a fuel flow issue.

Simple things, loosen cap when running to see if it improves, this is from a plugged vent in the cap.

Pull the filter and check for water / contaminates, while filter is off check for flow, out of the tank.

The next issue could be a bad lift pump, you will need to pull the input off the injection pump, feed fuel to the injection pump from above the pump from a new source like a funnel and while running check the output from the tank and the lift pump.

 

[huntersprings]

I hope you're right about the vent cap. I did open the stop cock while I had the filter off and the fuel was hitting the side of the cap underneath. Didn't know what was normal but seemed slower than I expected.

I've seen post where people blow a little air back into the tank in case something has blocked the flow coming out of the tank. Would the fuel line leading to the filter reservoir be the line to blow into and would that also be the line to drain the fuel tank if need be?

Thanks

 

[Tx Jim]

Ditto on "is tank venting"? IIRC my M4900 had fuel tank vent hoses. Water separator housing has a long history of passageway getting blocked. I once owned a M4900 that had a clogged screen in the water separator fuel cut-off valve.

 

[huntersprings]

Fingers crossed. Won't get to check it till the weekend.

 

[huntersprings]

Fired my tractor up last night after work, loosened cap on fuel tank and it climbed up a pretty steep hill without loosing power. My weekend is looking better.
Thanks guys!

 

[huntersprings]

Problem solved but it wasn't the cap. Loosening the cap did improve the fuel flow problem and I thought it was fixed until I hooked up a mower. RPMs dropped and the tractor bogged down again. I pulled the fuel line going from the tank to the filter and the flow was there but not great. Took off the cap and blew and little air toward the tank and heard the air bubble through the fuel. The flow immediately doubled.
When the fuel level gets low I plan to drain the tank and see if I can vacuum out any trash that might be sitting in the bottom of the tank. Love this forum and appreciate the helpful post.