FLU-419 fuel question - part above filter housing

talex419

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Hi, I'm new here and this is my first post.

I bought a FLU419 a few weeks ago, and it has been quite an adventure in learning about these and fixing the issues I've found with it so far. I'm an aerospace guy so it's in my wheel house. I think I got lucky, it has the "Overhauled at RRAD" plates (2009), and only 53 hours on the engine since that. Seems like a really clean one.

This is not a troubleshooting thread, as I have already found and fixed the source of my fuel system problem. On mine, the main air leak was a missing crush washer on the banjo fitting at the fuel inlet to the lift pump. I also had to replace the hand pump primer thing, fuel filters, the gasket at the strainer, and all the fuel lines.

My question is, what is this unlabeled part above the fuel filter housing? I can't seem to find any information as to what it is or what it does. See attachment.
 

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talex419

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Ahh, so it measures the pressure difference between before the filters, and after? I'm guessing this gives some sort of indication if the fuel filters are clogged and need replacement, the pressure drop would be larger. Does it flash a light on the dash or something?

The fact that it can be removed answers my question there, thanks.
 

Guyfang

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The pressure switch is indeed, as FLU Farm said, part of the STE/ICE-R diagnostic system.
Test step numbers:

24. FUEL SUPPLY PRESSURE Measures fuel pump outlet pressure. (Before fuel filters)
26. FUEL FILTER PRESSURE Detects clogging by opening a differential pressure switch across secondary fuel filter. (After fuel filters)
 

Speedwoble

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I haven't got around to it yet, but it sure seems like there's some 3,000 feet of unnecessary wiring and other stuff that could be eliminated...which would make the FLU more reliable.
Oh? Are you aware of a single issue traced back to the diagnostic wiring?
I agree it is cluttered, but the pin out is available and it makes a handy test point with a multimeter. Not that I have used it as such.

{edit, not trying to be sarcastic or poke FluFarm any more than I usually do. Just honestly curious as I don’t think I have seen issues traced back to the existence of wire. Most issues have been due to the lack of wire where rats chewed it.I would hate for the FLU to get a reputation for un-reliability without modifications.}
 
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talex419

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So far my gut feeling is that everything there on the FLU that was made by Mercedes is going to be fairly reliable (except maybe the shifter bushing, and a few other known issues). It's all the add-ons and things that could potentially cause issues (like fuel system leaks originating from this pressure switch thing). I agree that non-critical wiring like the diag stuff can't really cause reliability problems as the truck will still work without it, but things like unnecessary additional fuel system plumbing, I think I plan to get rid of.
 

The FLU farm

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Oh? Are you aware of a single issue traced back to the diagnostic wiring?
I agree it is cluttered, but the pin out is available and it makes a handy test point with a multimeter. Not that I have used it as such.
To me, the diagnostic system as a whole is a lot of useless wiring and hardware. Of course, I'm one of those who when getting a new-to-me or new vehicle start removing things I don't need or like. Unlike most, who add things instead.

And when I do add something, like the "extension hoses" from the backhoe's connectors to the loader (for the snow blower), and the current situation, running cables for the front mounted electric winch, it's painfully obvious how many essential hoses and electrical cables and wires there already is. Consequently, access to many things is quite cramped, or almost nonexistent.

You may recall me mentioning getting rid of the blackout lighting, and even the headlights. Like the diagnostic wiring, those are things I don't need or use.
While this 16,000-lb. pig will never rival a Lotus, I still believe that less can be more. Plus, it'd make it a bit easier to work on.
 

talex419

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Ooh yeah, I think I'll ditch the blackout lighting as well, I have no use for this. I'm not going for a restoration in any way on this FLU, it will be primarily a tractor, a work vehicle, and then also a fun mutant art project. It will be getting a non-military paint job, custom LED lighting, etc.
 

talex419

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Yep, everyone's project goals are different. I certainly can respect the pure utilitarian, "it just needs to work" thing. For me, this FLU is more than a piece of equipment, I will use it as such, sometimes, but at other times, I'm doing to do weird art stuff with it. These are already strange machines, in this oddly beautiful industrial art kind of way, so I'm inspired to do something with that, as well as the maintenance and fixing up of the machine of course, and making its core bits more reliable.
 

The FLU farm

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For me, this FLU is more than a piece of equipment, I will use it as such, sometimes, but at other times, I'm doing to do weird art stuff with it. These are already strange machines, in this oddly beautiful industrial art kind of way, so I'm inspired to do something with that...
Then it sounds like the HME would be the perfect version for you. Those look like they're made to be at Burning Man, as delivered.
 

peakbagger

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The diagnostic wring was added on in the US after it left Mercedes factory. it obvious they attached it on after it was assembled. One or two folks claimed to have removed the entire harness. There is current shunt near the battery box that have given a few folks issues with corroded connections. The student handout in the Misc Technical Manual section has more info on the STE/ICE diagnostic system

I would suggest leaving the black out lighting alone, that is Mercedes factory wiring and heavily integrated into the electrical system. Long ago my entry into the SEE world got delayed by having to trace and diagnose the electrical system to repair where a rat had chewed through the main harness without a wiring diagram (not available then but now available to download thanks to a forum member) and that blackout wiring is something I would not mess with.
 

The FLU farm

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There is current shunt near the battery box that have given a few folks issues with corroded connections.
My shunt's still there, but only because it's hard to get to. And after seeing how corroded the through-the-frame connector below was, I'm surprised that anything works correctly.
I'd like to hook the positive cable for the winch to that connector, but have so far only managed to get the nut on the inside of the frame loose, where the cable to the starter is connected.

And speaking of getting rid of, I'd really like to eliminate the master switch (winch installation related). What are your thoughts on that?
 

peakbagger

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My shunt's still there, but only because it's hard to get to. And after seeing how corroded the through-the-frame connector below was, I'm surprised that anything works correctly.
I'd like to hook the positive cable for the winch to that connector, but have so far only managed to get the nut on the inside of the frame loose, where the cable to the starter is connected.

And speaking of getting rid of, I'd really like to eliminate the master switch (winch installation related). What are your thoughts on that?
Funny you ask, my master switch is stuck on. I can turn it but its stays engaged. There are several running lights that stay lit so I have to pull the battery terminal whenever I am not using it. EI does not stock the switch. Its on the very long "list" of things to chase ;)
 

The FLU farm

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Hmm. I bought a new switch for the first SEE, since that one seems to be acting up. I can post the part number later and maybe you can confirm if it's the correct one or not.

Anyway, shouldn't everything go off when the light switch is turned to "everything off"?
 
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