TC35 fuel filter problem SOLVED!

[jedjoe]

Haha! Great minds do think alike....they also persist! And to persist one needs pizza...

 

[Harry in Ky]

I'm betting the blockage (if that's what it was) was more likely on the fuel tank to filter side, and the suction from the supply pump pulled air from the return line into the filter base. Seems more likely to me than the return line being somehow blocked.

 

[Jerry/MT]

I'm betting the blockage (if that's what it was) was more likely on the fuel tank to filter side, and the suction from the supply pump pulled air from the return line into the filter base. Seems more likely to me than the return line being somehow blocked.

+1

 

[Jerry/MT]

Ok, so yesterday I had removed the entire filter bowl assembly and cleaned everything thoroughly. There was absolutely nothing obstructing or limiting any one of the three orifices. I did not think to check whether that return orifice was before or after the filter. I believe it was AFTER the filtering but I can't swear to it.

I went back out about 90 minutes ago and took off the return line from the filter bowl assembly. Ran pressurized air through that line AGAIN. Then, reconnected the line after first ensuring that the bowl was full.

I then went out and did another long mow at about 2500 rpm engine speed. This is the rate that always produced the symptom within 15-20 minutes of mowing.

Guess what?? NO LOSS of height in the bowl!! Ran the tractor at that mowing speed for well over an hour and the bowl stayed full!!

What I did differently this time I am at a loss to define. It worked, but darn if I know WHY IT WORKED... The lift pump will likely show up in the next few days, and I have 30 days to return it without anything more than the shipping cost. So...I'll hold on to it for the next couple of weeks as insurance. I know it's almost certainly not the problem, especially since if it WAS the pump the problem couldn't have resolved WITHOUT replacing it. I just don't want to jinx the repair by sending the pump back prematurely. Call me superstitious.

If anyone out there can offer me a decent explanation as to why it worked this time but did not work the previous 4-5 times I'll buy you a pizza...

My relief that it may be fixed is tempered with the need to give it a few weeks of consistently working without incident. But perhaps (knock on wood), I'm done with this problem. I just wish I could tell all future TC owners with the problem the actual fix.

Thanks all

Glad you got it running. My thoughts on why your filter bowl kept running low implies that the supply passages between the tank and the filter bowl were restricted and the lift pump was sucking down the bowl through the fuel filter vent to the return to tank line since it probably is not checked.

For further reference, you can check a lift pump by removing the outlet line that goes to the injector pump and cranking the engine. If it the lift pump is working, you will see a big gush of fuel from the lift pump discharge port. If it doesn't or if it dribbles or is intermittent, the pump is bad.

 

[jedjoe]

I removed the fuel and return lines, checked them for deterioration on restrictions, blew them out thoroughly, etc. I then completely drained the tank, using a white cloth in a fuel funnel to look for any material that came out with the fuel. I then flushed the tank with clean fuel and even diesel conditioner. There was nothing in the tank...nada...zip. I then reinstalled the lines, removed and thoroughly cleaned and inspected the filter bowl assembly, etc. Put everything back together. Ran the tractor for 40 minutes at full engine speed (mowed another field). For those 40 minutes, the filter bowl stayed full. Thought I had finally addressed the problem. Next day, went out to mow another field and the symptoms all returned, same as before, fuel level dropping in the filter bowl assembly after about 15 minutes of tractor use. Arrrrgggghhhh!!!

While it seems to make no sense to do it, I will now replace the fuel lift pump. Yes, I agree that the problem should be between the tank and the filter assembly. But then the work I did should have fixed it. Since I had the new lift pump from Messick's, I might as well try it and see what happens. Promise to update this link after I change out the pump, but that won't be until this weekend.

 

[thclimer]

I removed the fuel and return lines, checked them for deterioration on restrictions, blew them out thoroughly, etc. I then completely drained the tank, using a white cloth in a fuel funnel to look for any material that came out with the fuel. I then flushed the tank with clean fuel and even diesel conditioner. There was nothing in the tank...nada...zip. I then reinstalled the lines, removed and thoroughly cleaned and inspected the filter bowl assembly, etc. Put everything back together. Ran the tractor for 40 minutes at full engine speed (mowed another field). For those 40 minutes, the filter bowl stayed full. Thought I had finally addressed the problem. Next day, went out to mow another field and the symptoms all returned, same as before, fuel level dropping in the filter bowl assembly after about 15 minutes of tractor use. Arrrrgggghhhh!!!

While it seems to make no sense to do it, I will now replace the fuel lift pump. Yes, I agree that the problem should be between the tank and the filter assembly. But then the work I did should have fixed it. Since I had the new lift pump from Messick's, I might as well try it and see what happens. Promise to update this link after I change out the pump, but that won't be until this weekend.

Well that is discouraging.

Hope the pump solves the problem.

 

[jedjoe]

Okay, so I had a bit of time this afternoon and thought I would go ahead with installing the new lift pump. Attached are three photos. The first is the top of the old lift pump after removal. Upon removing the cover, I inspected the inside of the pump. Looking carefully (and not really knowing what I was looking for) I did find this piece of the pump membrane broken off and inside the assembly. I pulled it to the side so that you could all see it easily. It obvious broke off from the outlet valve membrane. If I understand how this pump works, the shaft on the bottom of the pump is pushed in an out by a cam in the engine. As the shaft is pushed up by the cam, fuel is pushed out of the pump housing. Then the shaft extends back to engine, pulling new fuel in from the supply into the assembly for the next cycle of ejection. If that's right, then it would seem that this broken material compromises that process, by pulling fuel back into the pump from the wrong side and substantially limiting the efficiency of the pump. If I have that wrong, feel free to correct me.

Whether this broken outlet valve is the culprit causing my problem is anyone's guess. I'll have the run the tractor fast and long to see if I can recreate the "air inside the bowl" problem. The idea of air being introduced into the filter assembly from the return line still makes the most sense, but why start doing that now after more than 17 years of it never happening?? The main fuel line is not restricted or blocked in any way and the tank has been thoroughly flushed, something that I am now confident about after my previous efforts this past weekend.

I'm running out ideas here, so feel free to chime in if you have a better or another theory as to what is happening.

 

[thepumpguysc]

It’s as good a theory as any..
But the proof is in the pudding..

 

[jedjoe]

If the air is coming from the fuel return line (being pulled from air in the tank), would I be correct in assuming that I could fix that problem by installing a check valve on that return line? So that only excess fuel could move one way back to the tank, but not permit air to travel from the tank back to the filter bowl assembly?

 

[Harry in Ky]

I keep going back to logic of the return line to begin with, and then to the logic of a check valve. Why would there be excess fuel in a filter base that operates under vacuum from the supply pump? If it were me, I would snip the hose and plug both open ends. Then see what happens.