M929 Questions

[Russ Knight]

What's the valve between the driver's door and seat near the rear of the cab for? I tried turning it, but it appears to be stuck. I haven't traced the lines out yet. Is it the valve that switches the fuel tanks perhaps? Also, does the dump bed latch close automatically when the bed is lowered all the way?

 

[BKubu]

That is the fuel tank selection switch. I believe there should be a data plate under the switch that indicates left and right.

 

[Russ Knight]

That is the fuel tank selection switch. I believe there should be a data plate under the switch that indicates left and right.

There is some kind of floor covering in this truck. I'll get a crescent wrench and see if I can move the handle. Thanks!

 

[M35A2-AZ]

I would take it out and clean it and replace the o-rings and it will be good as new. If it is pointed to the back of the truck it is the left tank if it is pointed to the drivers seat it is the right tank. But someone may of put it on wrong.

 

[Mullaney]

What's the valve between the driver's door and seat near the rear of the cab for? I tried turning it, but it appears to be stuck. I haven't traced the lines out yet. Is it the valve that switches the fuel tanks perhaps? Also, does the dump bed latch close automatically when the bed is lowered all the way?

.
I FOUND IT!

The link below is the "how to" guide on rebuilding the fuel valve on a 5-Ton. Old is good! Created back in 2011

5 ton fuel tank selector valve cleaning/rebuild

Well,After searching the threads and getting questions from other members,I decided to cover the cleaning /rebuild of the fuel tank selector valve used on the M39,M800 and possibly M900 series 5 tons. First off,this valve is a common air leak in the fuel system on the 800 series trucks with...

www.steelsoldiers.com

 

[Russ Knight]

.
I FOUND IT!

The link below is the "how to" guide on rebuilding the fuel valve on a 5-Ton. Old is good! Created back in 2011

5 ton fuel tank selector valve cleaning/rebuild

Well,After searching the threads and getting questions from other members,I decided to cover the cleaning /rebuild of the fuel tank selector valve used on the M39,M800 and possibly M900 series 5 tons. First off,this valve is a common air leak in the fuel system on the 800 series trucks with...

www.steelsoldiers.com

Thank you!!!

 

[TechnoWeenie]

Now would be a good time to read the -10 TM front to back

 

[Russ Knight]

Now would be a good time to read the -10 TM front to back

Uh, no. I'd rather dig a ditch. But I agree, I should.

 

[TechnoWeenie]

Uh, no. I'd rather dig a ditch. But I agree, I should.

You're driving around a 40K+ lbs truck... and you don't even know where the fuel selector lever is?

Pray you don't get into an accident, as the other party's attorney is gonna have a field day...

This isn't a passenger car you just hop into and drive, you know.

 

[Russ Knight]

You're driving around a 40K+ lbs truck... and you don't even know where the fuel selector lever is?

Pray you don't get into an accident, as the other party's attorney is gonna have a field day...

This isn't a passenger car you just hop into and drive, you know.

Good grief. This is my fourth MV, my third 5 ton. My last truck was a MK23. I've owned these trucks in various configurations since the early 90's. While I certainly don't claim to have an exhaustive knowledge of these vehicles, I know how to drive these trucks, service these trucks, understand the handling / braking characteristics, etc. However, none of the other trucks had dual fuel tanks. It was a simple question about a minor mechanical detail. I appreciate your concern, but with all due respect, I'll stay in my lane and invite you to stay in yours.

 

[TechnoWeenie]

Good grief. This is my fourth MV, my third 5 ton. My last truck was a MK23. I've owned these trucks in various configurations since the early 90's. While I certainly don't claim to have an exhaustive knowledge of these vehicles, I know how to drive these trucks, service these trucks, understand the handling / braking characteristics, etc. However, none of the other trucks had dual fuel tanks. It was a simple question about a minor mechanical detail. I appreciate your concern, but with all due respect, I'll stay in my lane and invite you to stay in yours.

My 'lane' is to protect myself, and the hobby. If the shoe does not fit, then clearly it's not yours.

 

[DeMilitarized]

My 'lane' is to protect myself, and the hobby. If the shoe does not fit, then clearly it's not yours.

The tone of how things are said/read can change the meaning drastically compared to what was intended.

 

[Russ Knight]

My 'lane' is to protect myself, and the hobby. If the shoe does not fit, then clearly it's not yours.

Good enough. Peace, my friend.

 

[Russ Knight]

Back to the topic. I used a crescent wrench today and broke the valve loose. It operates smoothly now, and I swapped tanks with no issue. I think I'm going to need a sending unit in the driver's tank, it's very unstable. Gauge moves wildly back and forth when the vehicle is moving. Where is the best place to source one?

 

[DeMilitarized]

Back to the topic. I used a crescent wrench today and broke the valve loose. It operates smoothly now, and I swapped tanks with no issue. I think I'm going to need a sending unit in the driver's tank, it's very unstable. Gauge moves wildly back and forth when the vehicle is moving. Where is the best place to source one?

How long did you let the truck run for before you said “it works now”? It takes mine about 10-15 min at idle to eat through all the fuel in the lines then dies. I think my passenger tank pickup is broken.

 

[Russ Knight]

I drove it about 25 miles after switching the tanks.

 

[TechnoWeenie]

I drove it about 25 miles after switching the tanks.

Double check your grounding at the tank. It's almost always a ground issue since the fuel level circuit uses the tank/straps/chassis as return ground path.

You can pull the valve and clean it. It's messy, but doable.

One thing you might want to do, provided you have spare fuel filter, is dump some oil and ATF in the tank, along with some B12 Chemtool or Seafoam. There are a ton of detergents in oil and ATF that will clean out a lot of gunk. Just beware that you're going to.. be dislodging a lot of gunk.. so you're probably going to clog your filters pretty quick, if the tank/lines have never been cleaned...I wouldn't use waste motor oil for this, just regular oil, pretty much any grade will do. 'High mileage' oil tends to have more detergents... I would suggest doing it on no more than 1/4 tank and dumping a couple gallons of oil in there... I'd also double dose your fuel with PowerService... I think the big jug is like $30 and treats 250 gallons.. or ~20 for the one that treats ~100 gallons. I'd just dump the whole thing in a full tank... Should clear out any lines halfway decently, but again, make sure you have a spare fuel filter on hand first.

I do the above with all my 'new' trucks....and it usually clears up any small issues... and quiets the engine down a bit..... It has a different note to it.

 

[Russ Knight]

Double check your grounding at the tank. It's almost always a ground issue since the fuel level circuit uses the tank/straps/chassis as return ground path.

You can pull the valve and clean it. It's messy, but doable.

One thing you might want to do, provided you have spare fuel filter, is dump some oil and ATF in the tank, along with some B12 Chemtool or Seafoam. There are a ton of detergents in oil and ATF that will clean out a lot of gunk. Just beware that you're going to.. be dislodging a lot of gunk.. so you're probably going to clog your filters pretty quick, if the tank/lines have never been cleaned...I wouldn't use waste motor oil for this, just regular oil, pretty much any grade will do. 'High mileage' oil tends to have more detergents... I would suggest doing it on no more than 1/4 tank and dumping a couple gallons of oil in there... I'd also double dose your fuel with PowerService... I think the big jug is like $30 and treats 250 gallons.. or ~20 for the one that treats ~100 gallons. I'd just dump the whole thing in a full tank... Should clear out any lines halfway decently, but again, make sure you have a spare fuel filter on hand first.

I do the above with all my 'new' trucks....and it usually clears up any small issues... and quiets the engine down a bit..... It has a different note to it.

So, to be clear, do I do this all at once, oil, Seafoam, and 2.5 quart Power Service all on 1/4 tank? I have a Freightliner flatbed delivery truck that is running like crap, it needs it too.

 

[TechnoWeenie]

So, to be clear, do I do this all at once, oil, Seafoam, and 2.5 quart Power Service all on 1/4 tank? I have a Freightliner flatbed delivery truck that is running like crap, it needs it too.

If you want to get stuff out of the tank and lines, then yes. You can also run biocide if its been sitting for a while.

If you want to purge the pump, injectors, etc and clean them out, then you disconnect the supply line going to the IP/PT pump, and your mix of seafoam, power service, ATF/OIL mixed into a gallon jug and have the engine suck it all in directly instead of pulling from the tank.

That's one of the great things about older diesels like the NHC250, and to some extent the 6cta8.3.... looser tolerances mean it's not as picky about fuel... Do NOT let it run out of fuel though.. It uses fuel as lube for the pump.

I literally ordered a gallon of MMO, a gallon of TCW3 (2 stroke oil), 2 cans of seafoam, 2 cans of wallyworld version of seafoam, and a gallon of ATF, because this convo reminded me I needed to do it to my new truck.... I plan on doing a pump/injector purge which means I'm gonna take half of the above, dump it in a pail, and suck it directly in, and the remainder will be dumped into the fuel tank and diluted. By sucking it in directly, it's not diluted with fuel.

I couldn't get powerservice diesel kleen, otherwise I would have added that to my list...

The seafoam will provide the immediate cleaning ability, the ATF has detergents, the TCW3 and MMO provides lubricity. All of which are readily combustible in a diesel engine with no issues.

You really don't need to do a purge that often, but my truck is 30 years old and I guarantee it's never been done.

TCW3 is something I suggest in every tank...1 oz per gallon, but more won't hurt. the ULSD of today doesn't have the lubricity that older diesel does... which the engine was designed to run on..

It's actually very common to dump seafoam 100% strength into diesel fuel filters when changing them.... to clean things out... This is just a longer, more complex version, on steroids.... when purging....

By diluting it with fuel in your tank you have a gentler effect over a longer time, as the chemicals work in the tank/line.

That's why I do both. Half to do a quick deep clean of the injectors/pump, the other half to continue cleaning the rest of the system, for the remainder of the tank.

You will notice a quieter running engine on the TCW3 alone..

 

[TechnoWeenie]

To the above - If you're looking at cleaning/freeing up the fuel selector valve, then you can disconnect both lines and run both of them into your pail that you're sucking your purge solution from, then just keep moving the valve back and forth as it's sucking it in, 30 seconds or so on each side, alternating...

The problem with that, though, is it goes through the fuel filter, which is MASSIVE, and already full of fuel. You'd be better off pulling the valve and cleaning manually, IMO... or just wait for the mix in the tank to make its way through... if it's not critical right now.

Also, as with most things on these trucks, they tend to bind/seize when not used... so use it... alternate tanks frequently.....

--Also, if you don't believe me on the TCW3... dump a gallon in your fuel tank (half tank or more is better, so it's not being wasted)... Start your truck and wait a couple minutes..... you'll notice it gets quieter as soon as it makes its way through the filter and into the engine... Funny what happens when things are getting lubed properly..