FE35 air in injector pump

My FE/MF35 (not sure which it is!) with 23C has a problem at the moment in that I'm constantly getting air in the injector pump, which will cause the tractor to stall.

At first I thought it was just due to bouncing over some rough ground, shaking up the fuel and sucking through some air. But now its happening very often on flat ground with a full tank of fuel. It appears most when I'm working the tractor - not so much at low rpm/load. I suspect because the auto air bleed off system can't bleed it off quick enough? At the moment I'm trying to mow 5 acres with a 4 disc mower, its cutting out and I'm having to bleed the pump about every 2nd lap around the paddock.

There is no sign of air in the rest of the fuel system, cracking the top bleed screw on the pump, then bleeding the injectors gets it going every time. I cant see any fuel leaks, although the small cyindrical shaped device attached to the bottom of the pump does appear a bit weepy and the cork gasket between this and the pump is a bit swollen.

Where is this air getting in? Could it be a dodgy pump gasket somewhere like the one I mentioned?

Make sure all the filters are sealed correctly, no twisted O rings. Also check the constant bleed oriface fitting on top of the filter base. The small hole must be open. If plugged any air in top of base can't escape, and then gets to the injection pump causing shutdown. Hole is small, maybe .020 or .030 Inch size. If I remember correctly it is in the banjo bolt on top of the final filter. When it gets plugged it can drive you nuts, as engine will run awhile until it gets a gulp of air again. Happens on Perkins engines too, Just in case Tony is reading this!!!

Also check the gauze filter inside the tank, on top of the drain tap.
partial blockage of this can let the tractor run but then when you
need to get some work done it will stop/starve of diesel. By the
time you get to bleeding it, enough diesel has made it through the
gauze to allow the tractor to start again. Another possible problem
is the fuel lift pump. It could have a ruptured diaphram, allowing
some engine fumes to mix with the diesel, giving the same effect as
an air bubble.
Let us know what yoy find please......Sam

Ok, I've dismantled and cleaned the low pressure side of the fuel system. I haven't replaced the fuel filters yet as I'm not near anywhere at the moment that I can get them. But was told they were new when I purchased the tractor and its only done 80hrs since then, so I cant see they'd be the problem.

The fuel tap/bowl did not have a screen on it - I was hoping this being clogged would have been the problem but no joy. There was a bit of crap in the fitting which screws into the tank but not enough to cause a problem. I dismantled the lift pump as well. I put it all back together and made sure everything was tight. If i remove the pipe that feeds the injector pump, I can pump the lift pump and get a small stream of fuel coming out so there didnt appear to be any major restriction.

I took it back out to the field with the mower and got about 30m before it started losing power and stalled again - bled the pump and got about another 20-30m and same thing. If anything its worse than before!

My lift pump has always been a bit weak I thought - whenever I've had to hand prime it just didnt seem to move a lot of fuel with each pump and I can never get a good spurt from the bleed screws - just a dribble, could this be a problem? It certainly sounds like a fuel starvation problem, I can drive it all day long at lower revs/load, it just seems to be at load ~1300-1500rpm that it dies.

Ok, it does sound like you have a fuel lift pump problem. possibly
either dirt in some of the valves or just a weak or busted diaphram.
On pumping the lift pump you should be sending fuel from the
bleed screws out at least 2-3 foot from the tractor. Try a new lift
pump they are not very expensive....I sell them for about
£17sterling.....does not take much downtime to cover that expense!
Sam

Yep, it was the lift pump. Did the 2hr dash to my tractor parts guy and picked up a new one, noticed the difference when priming immediately. Finished cutting my hay paddock and it didn't miss a beat!

Thank goodness you have got it fixed....It is always nice to know
that we helped!
Sam