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.

 

[thepumpguysc]

I don’t think there’s enough pressure to open a check valve..
Do u have a knob on your inlet banjo bolt.??
If yes, try turning it the other way and see what happens..

 

[jedjoe]

If replacing the damage lift pump doesn't fix my problem (and I am now expecting that it will not), what I try next is simply temporarily crimping that return line to connects to the top of the filter assembly with a hemostat. If the air is entering the filter assembly from there, then it should stop the problem without preventing the return line from still running from the back of the injector assembly back to tank. I'm sure I have no leak from a crack in the filter assembly, so it has to be from the return line connection.

Here's another thing to consider. The return line leaving the injectors connects to the line to tank and the line to filter assembly using a "T" fitting. Should it matter which part of the "T" goes to which line? I thought I once heard that, at least in waste water household plumbing, It's imperative to use a "Y" fitting vs. a "T" fitting when joining three pipes. I think "T" fittings can cause a suction in a cross line when fluid is moving rapidly along the straight line place on the connection. If I'm right, the "straight" linkage on the "T" should be the line from the injectors to the line heading back to the tank. The bottom of the "T" should go to the filter assembly. Right now, I have it the other way around, possibly causing air to be sucked from the tank toward the "T" connector.

I may try switch those lines and seeing if that makes any difference. It would be amusing if that was the problem! When I replaced those lines many weeks ago, I did not bother to pay attention to which line went to which part of the "T" connector. The devil is in the details!

 

[brown1032]

Your post doesn't say if your losing power, mine did at higher rpm. Replacing the lift pump solved the issue for me Same machine mine is a 2003. And that is all I did, had an issue found the same situation here on TBN, replaced the pump, solved. Good Luck.

 

[jedjoe]

I would occasionally lose power, but not consistently. What would happen is that, if I didn't pay attention to the height of the fuel in the filter bowl, I could drain the bowl completely and the tractor would then stall out. I would then need to reprime the injectors (always a pain in arse)...

 

[brown1032]

Mine never stalled out only lost power (rpm) happened a few times started doing research here and ordered the lift pump and installed. Look forward to hearing how yours runs with the new lift pump installed.

 

[jedjoe]

Going back to theory that air could be entering the filter bowl through the fuel return line (via the tank), here is a diagram I found online from a site that sells fuel line check valves. While the arrangement on this diagram is different from my TC 35 (especially with the lift pump being BEFORE the filter assembly vs. the pump being AFTER the filter), it does reveal the probable value of having check valves in a fuel system to prevent things moving in the wrong direction.

I have order a small in line check valve designed for diesel that I will probably try.

 

[jedjoe]

So I got a three pack of these 3/16" check valves. They were only $7.99 for the three of them. Rated for fuel oil (including diesel). If my little experiment with crimping the return line to the filter assembly works, I will likely install one of these valves on the section of the return line that runs up to the tank. Should stop fuel (and then air) from being suctioned back down that line and into the filter bowl...

 

[jedjoe]

So crimping the return line where it enters the top of the filter bowl fixed it, at least for a solid hour of running the tractor at high throttle and mowing a sense field. The air is DEFINITELY coming in from that location. And the only logical place to access that air has to be from the return line to/from the tank. I theoretically could run the tractor this way indefinitely, with that small return to filter bowl just closed off permanently…right? All I think I would be sacrificing is the warming effect of the recycled fuel from the injectors to prevent gelling in really cold weather. But I use an antigelling additive in the winter and have a block heater for when it gets really cold here.

I think I will try installing the check valve on that return run to the tank. Providing there is enough fuel pressure to keep the valve open when it heading back to the tank, it should stop the suction of air back the other way. Not a bad experiment for $7.99 either way. If it doesn’t work, I think I’ve still essentially solved the problem!

 

[thclimer]

So crimping the return line where it enters the top of the filter bowl fixed it, at least for a solid hour of running the tractor at high throttle and mowing a sense field. The air is DEFINITELY coming in from that location. And the only logical place to access that air has to be from the return line to/from the tank. I theoretically could run the tractor this way indefinitely, with that small return to filter bowl just closed off permanently…right? All I think I would be sacrificing is the warming effect of the recycled fuel from the injectors to prevent gelling in really cold weather. But I use an antigelling additive in the winter and have a block heater for when it gets really cold here.

I think I will try installing the check valve on that return run to the tank. Providing there is enough fuel pressure to keep the valve open when it heading back to the tank, it should stop the suction of air back the other way. Not a bad experiment for $7.99 either way. If it doesn’t work, I think I’ve still essentially solved the problem!

While your experiment does seem to have solved your problem and may work going forward, I'm still curious and I'm sure you are as well as to what has changed that caused your filter housing to lose its fuel level. Yours as well as thousands of other TC35A's have run without a clamp on the return line.

Its almost like your tank has a vacuum on it and will not allow the fuel to flow into your filter, but with a vent line being on your filter the fuel is allowed to be pulled from it and replaced with air from the vent. Its an example of the path which offers the least resistance will be taken.

Is there a pressure rating on the pressure required to open the check valves that you purchased?

 

[jedjoe]

While your experiment does seem to have solved your problem and may work going forward, I'm still curious and I'm sure you are as well as to what has changed that caused your filter housing to lose its fuel level. Yours as well as thousands of other TC35A's have run without a clamp on the return line.

Its almost like your tank has a vacuum on it and will not allow the fuel to flow into your filter, but with a vent line being on your filter the fuel is allowed to be pulled from it and replaced with air from the vent. Its an example of the path which offers the least resistance will be taken.

Is there a pressure rating on the pressure required to open the check valves that you purchased?

That's the thing that drives me a bit crazy about this. The tank vents perfectly, so it's not a vacuum build up in the tank itself. It's not a blockage in the tank or near the tank exit, as I completely drained the tank, rinsed it out with diesel and diesel conditioner, and did not get even a speck of particulates out of the tank. It's not the main fuel line as near as I can be certain, as when I drained the tank I was able to empty about 9 gallons of diesel in about 12 minutes of gravity draining. That's a rate of flow FAR in excess of what the engine could ever demand. And I watched it drain for that entire time; there was never a moment where the flow rate slowed until it reached that last quart or so of diesel and there was simply less weight of fuel above the outlet to encourage draining.

I will admit that while I changed out the two small sections of the return line with brand new OEM 3/16" fuel line, I did not change out the longer section to the tank, nor did I change out the main fuel line. I did inspect them, however, and they absolutely looked and functioned perfectly. At one point, I wondered whether the INSIDE of the main fuel line had degraded over the years, and had somehow created a rougher surface where friction could slow the rate of fuel movement. But the speed of draining I mentioned above seems to negate that theory. The diesel flowed out rapidly and consistently under gravity, and at a pace that would far exceed even a high rate of fuel use by the engine.

I don't have an specs on the pressure required to open that soon to arrive 3/16" check valve. I can't imagine it's any more than a few psi, but I'll have to wait and see. If it doesn't work, it was but a small investment. I can only hope that this thread is read by someone who has had this same problem AND is now entirely CERTAIN of what is the etiology of the symptom. It's become pretty clear to me that I am far from the only TC owner who has encountered this exactly same issue