Trailfinder

My M998 just sprung a leak. Diesel is dripping out of the air cleaner housing. Does anyone know how to correct this? I suspect fuel tank vent line/filter.

WillWagner

Air cleaner?! Does it have a fording kit? The tank vent might be plumbed to there. I'd check the oil for having fuel in it too.

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Trailfinder

Has a fording kit. Manual states a clogged vent filter will cause vacuum in tank/fuel problems. Thanks for suggestion on checking oil. Several important items are also attached to the main vent line.

Just found this on:

Hummer Trivia & Misc Info

Don't Modify the Air Intake System

Even AMG has not covered their air cleaner and gearbox vent system interrelated functions in HUMMER Manuals or as I recall not even during Tech training sessions, so I cannot hope to cover it properly here ..guess you could just trust me on this one!

BUT ..basically it all has to do with the orifice of vent tube, p/n 12340799. Just where it is located inside the air cleaner, how it is positioned relative to the direction of air flow, the velocity of air flowing by its orifice (venturi vacuum effect) that determines how well, if at all, the vent system functions. When too much vacuum was created it actually sucked diesel fuel into the air cleaner on the original HMMWV design. For that reason ever since there has been a separate fuel tank vent line run and it is always open to atmosphere ..never comes under a vacuum! If too little vacuum is created or
the reverse, incoming air pressurizes the vent system, guess you know what the results can be!

Now what?

Stonepicker1

We had a M998 do the same thing in Iraq in 2003. It turned out to be a bad lift pump.

Diesel fuel was leaking past the diaphragm and was being pushed through the vent system to the geared hubs / transfer case and then pushed out the air cleaner.

The M998 ran fine just took a few more seconds to start.

Just something to check, good luck.

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Trailfinder

I'll check that "lift pump" failure possibility. I am also going to see if removing the fuel cap eliminates the vacuum. If so, I will most likely have to run the fuel tank vent line independent of the main vent line. Thanks for the help!

sandcobra164

We had one at work do the same thing. It was a Marine Corps M998 with the fording kit and it would suck enough diesel to soak air filter in about 2 days time. The truck ran fine during all of this and we never did determine the cause. We checked all of the vent lines, (they were fine) as well as the lift pump. It was the only HMMWV I ever saw do this so it probably is a rare problem. The truck itself was driven very little at work and mostly spent it's time idling around our maintenance facility.