TC35 fuel filter problem SOLVED!

[jedjoe]

Hi All,

PLEASE GO TO THE BOTTOM OF THIS THREAD if you are looking for a SOLUTION to fuel levels dropping inside the fuel filter assembly during tractor use. You are, of course, welcome to read the entire thread.


I have been having a persistent problem on my 2004 TC35. When I run the tractor at a persistently higher RPM (such as when using a rotary cutter), the diesel in the filter bowl keeps dropping. If I neglect to check it periodically, I run the risk of the lines being sucked dry and the tractor stalling out (and the later aggravation of having to reprime the injectors). If I loosen the bowl, diesel easily refills.

I've done all of the obvious. Change the filter, blow out the fuel line and return line, drain the tank and ensure there are no blockages or sediment. Also have checked to ensure that the fuel tank cover is venting. Thanks to TBN, I've tracked down a number of threads that describe this same issue. I've drawn the conclusion that my lift pump is probably on it's way out and it's time to replace it. I order a new one from Messick's and it's on the way.

Question: Does anyone out there either have written instructions on how to properly remove the old pump and install the new one? Looking at it on the tractor leaves me with the impression it's probably a pretty simple job, but impressions can deceive and I'd greatly prefer to have the confidence of knowing exactly how to do it correctly. Also, are there any other parts I am going to need beyond the new pump? The hoses all look to be in good shape. The "collective expertise" of TBN members has never let me down. Thanks!

 

[Harry in Ky]

I guess I don't understand your logic. I thought the fuel routing from the tank went to the filter first, then to the supply pump, and on to the injection pump from there. Maybe I'm wrong on that?

 

[thepumpguysc]

It’s possible that u may have to “clock it” differently than received..
As u can see in the picture, there is a hash mark..
& u should ask if it came/comes w a mounting oring/gasket..

 

[JC-jetro]

Lift pumps are used when the gravity supply to the inlet of injector pump is not achieved. Do you have a suction pick up tube in your tank? of this was commercially done on fuel tank system (I.e , engine generator and such ) then there would be a suction check valve at the pick up line to avoid back siphoning into the tank. I checked it and they do call it "lift Pump". It seems removing 2 bolts with free up the device provide fuel inlet and outlet is removed first. I don't believe from a looks of the tip if it needs to be timed. If I removed it then I would not move and turn engine and put the matching spline in to the housing the same as I found it.

 

[jedjoe]

I guess I don't understand your logic. I thought the fuel routing from the tank went to the filter first, then to the supply pump, and on to the injection pump from there. Maybe I'm wrong on that?

My logic fails me as well. It doesn't make sense unless you consider that if the pump is not keeping up with the demand at the injection pump (as might be the case if I was running at a high throttle), a vacuum could be created between the lift pump and the injection pump. Then an air leak could introduce air into what should otherwise be a closed system.

Honestly, none of the past threads have appeared to actually create a solution that someone posted. It's obviously an issue in that vintage of tractors (TC 30, TC 35, TC 40). Solutions have been suggested (such as poor to no venting through the cap, blockages at the bottom of the tank, etc.) but none of them make sense when you consider the entirety of the symptoms.

The tractor is now 19 years old, and since the lift pump is a rather modest item pricewise to replace, I'm going to replace it and see what happens. I think I've done everything else that could be causing the problem.

 

[thepumpguysc]

It DOES sound as tho you’ve tried everything else..
Btw.. u don’t have to “time” the lift/supply pump.. it simply bolts on..
It’s operated by a cam lobe and if u feel like there’s to much pressure when you go to put the new one on.. just bump the engine to move the lobe..

 

[Harry in Ky]

As I see it for the lift pump to be the problem, it has to be trying to pull fuel through the filter faster than fuel can enter. The injection pump demands nothing. It has no vacuum or suction. Those engines survive quite well without supply pumps, just on gravity feed alone.

No matter how I review it, the problem still comes back to fuel supply, not the lift pump. Maybe getting air in through the return line on top of the filter base? I never understood the logic of that either, but what do I know?

 

[dlctcg]

@jedjoe - I have to agree that this seem much more likely to be a fuel supply issue to the filter bowl. Before changing the pump I would double check all the lines you already checked.

We had the exact same problem just 2 months ago on our TC40D, machine would start & run fine at low idle but as soon after idling up the fuel bowl would be half empty. Loosen the fuel filter bowl & it would fill right back up.

On ours - the fuel gravity flowed freely from the tank to the bowl when the filter bowl was removed. The fuel tank cap vented correctly, we actually removed the cap & cover the tank opening with cheese cloth to make sure it wasn't the cause. Finally, removed the return line at the fuel filter housing & from the engine fuel return (they are just tee'ed together), removed the fuel cap & then blew air through the line back to the tank... put it back together... Still have the same issue.

Thought maybe a collapsed hose but they were new less than 2 years ago, so opted to try the return lines again...

This time same as above, removed fuel cap, removed the return line at the fuel filter housing & from the engine fuel return, clamped off the fuel lines & removed them & sent a good amount of air through the return line back to the tank... also blew some air through the fuel filter housing ports... put everything back together & this resolved our issue.

So I would give it one more try prior to putting a pump in...

 

[Harry in Ky]

Makes more sense than replacing the lift pump.

 

[jedjoe]

Thanks to you all, this has been a productive thread. But I am still struggling with understanding why the bowl slowly fills with air (and not fuel). Where is the air coming from? Why, when I crack the seal on the filter bowl, does the bowl immediately refill? To try to better understand this (since NH does seem to supply such diagrams), I drew a diagram of the system as I understand it. Can you all look at the diagram and correct any inaccuracies?

Just for the record, I've check the venting cap (works fine) check for sediment/restrictions in the tank (nothing there), removed and thoroughly cleaned the fuel filter assembly (there were no restrictions of any kind) and tripled checked the on/off valve, replaced the two sections of the fuel return line (the one that comes from the back of the injector pipes and the other one that comes up from the filter assembly, replaced the "t connector" that joins those two lines as they connect to the main return line, blew out (several times) both the fuel line and the return line.

For the life of me, I cannot find a single problem with the fuel system at any point before it reached the lift pump. That's why I am considering changing the lift pump out (even though, you are all right, it's not logical).

I am not a fluid engineer. Consequently, I cannot make any sense of why this problem is occurring given what I have already done. How can it have anything to do with a tank blockage when the problem is immediately "corrected" when the seal is broken on the filter assembly (partially unscrewing the bowl)? The only thing that makes sense is that air is replacing where fuel should be in the bowl. But where does the air come from if the system is providing a positive pressure through the entire flow (see diagram).