TC35 fuel filter problem SOLVED!

[Harry in Ky]

I would be looking at the passages that involve the return line from the filter base leading up to the tee. I've never understood the need for that port. Most all the tractors I see with that type filter base have no such vent or return line involved. It's just fuel into one port, fuel out of another.

 

[jedjoe]

That makes sense to me. It seems that the only place for air to enter the bowl would be from that opening. It doesn't make sense to me either. I see the value of having a place for excess fluid/vapors/even air to go after visiting the injectors. It keeps everything moving in a loop from the combustion end of the tractor to the fuel storage area. Why it needs to connect back to the filter assembly doesn't fit.

I can temporarily shut off that one section of the return line (the section running from the filter assembly to the "T connector" with a hemostat (a medical clamp). And then run the system and see what happens. If I lose power after several minutes of mowing, then I'll know that somehow that one link in the system is essential. If, on the other hand, the bowl stays full and I don't lose power, then I may have my answer. Sometimes I wish that the New Holland engineers who design these systems would visit a site like TBN to explain their thinking.

Fortunately, if this fixes the problem, I can return to the pump to Messick's as long as I haven't opened up the packaging.

No matter what, when I do solve this problem I will be sure to post the fix, as it seems I am far from alone in trying to address it.

 

[jedjoe]

Okay, so I followed Harry in KY's suggestion and focussed upon the section of the fuel return line that runs from the top of the filter assembly to the "T connector" that joins the hose that runs from the back of the injectors to the main return back to the tank.

I crimped that short line with a pair of hemostats (two of them just to ensure I had no leakage for this experiment).

Result?: Was able to run the tractor at about 2500 rpm (mowing a field edge) for about 45 minutes with no loss of power/performance. In the recent past, that would have caused my filter bowl to nearly empty. This time, I still lost some fuel volume in the bowl, but only a drop of about 1/2 inch.

I guess I must be on the right track. What's still annoying is that for the last 18 years this was never a problem, and this summer it has been. I'm still flummoxed as to where the air is being introduced. It has to be a location in fuel loop that permits air to be pulled in. If it was a place that had positive fuel pressure, I would have a fuel leak, not the introduction of air. Right?

 

[thclimer]

Attached is a diagram of the fuel system and a description of how air is bled from it.

 

[Harry in Ky]

If I were fighting this, my next move would be to remove the bowl and filter. Remove the problematic return line from the filter base and blow some air into fitting it came off of, mainly to see if it connects to the inlet side of the filter element or the outlet side. That probably makes no difference either way, I'm just curious. Then I think I would swap some hoses around, run the supply from tank to the lift pump inlet and from there to the filter and on to the engine, thus pressurizing the filter. I prefer that to fighting air leaks on the suction side. Have done that many times with no ill effects. If the situation warrants, I will add an inline screen just ahead of the pump. In this case I don't see where that would be needed.

What to do with/about the return line would be based on results of all that. Leaving it intact might result in too much flow and pressure having a free flow back to tank. Then again having the port available might be handy for bleeding air from the filter base if/when needed. That's a judgement call at this point.

 

[dieselscout80]

I would be looking at the passages that involve the return line from the filter base leading up to the tee. I've never understood the need for that port. Most all the tractors I see with that type filter base have no such vent or return line involved. It's just fuel into one port, fuel out of another.

The return fuel from injectors is warm and can help keep a fuel filter from gelling if it is cold enough. That said it seems to dump in the fuel tank where I guess it could keep it warm too.

 

[jedjoe]

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

 

[Harry in Ky]

The earlier post from dlctcg describing an experience with a similar (if not the same) problem, in which it was stated that it was solved by basically removing lines, etc, and thoroughly blowing everything out. Apparently no parts were actually replaced. Sounds pretty similar to what you've done. That tractor has been working since then, now yours is as well. With everything back as originally configured? Kind of leads to the possibility of a minor blockage somewhere on the suction side of the filter that went unnoticed during all the attempts at finding a problem. Who knows?

At least you know it's running again and hopefully you're done with that.

 

[jedjoe]

You are right, it was the very same problem. And, interestingly, it was repeating the "fix" (as dlctcg did) that resulted in what appears to be the solution. Now time will tell.

I'd still be interested in any compelling theory that explains how a partial blockage in the return line could result in air entering the bowl

 

[dlctcg]

I wish I could explain it... but glad it worked!!! Maybe it just has something to do with NH TC's in CT....

When I was troubleshooting ours I called upon my brother who is head of a vehicle maintenance for a local town... He kept telling me "it is a fuel delivery problem, stop over thinking it. You have a blockage or collapse line somewhere... it is gravity fed".

Funny thing is after re-clearing the lines & it working... I picked up pizza (& a 6 pack) for him & his wife... I guess great minds think alike (besides we have pretty great pizza in CT... lol)