M35a3 fuel problem

Hey guys,My m35a3 was acting like it had a dirty fuel filter,so I changed it today.It starts fine but once in a while it acts like it is running out of fuel.It starts back up ok.Does anybody know if the injection pump has a filter or screen or any other fuel filters on the truck.I would like to know who the genious was who decided to mount the spin on fuel filter completely upside down.thanks,John

I would like to know who the genious was who decided to mount the spin on fuel filter completely upside down.thanks,John

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Never forget that your truck was built by the lowest bidder.

It's prob sucking air somewhere......did you tighten the filter good when you installed it? Does it have more than one filter?

I don't know A3's so I am guessing.

The old filter was so tight I had to use a set of giant channellocks to get it off.

Mine was on real tight too.

Catman on here is a Caterpillar mechanic and in an earlier thread addressed the fuel filter issue:

Also, Cat engineers and the Army did not want maintenance people prefilling the fuel filter canister when changing spin on filters. That is a No No. Contaminated fuel (dirt) can get into the filtered side of the filter. All the Cat books for many years tell you that. Never fill the filter!

The unit fuel injectors will not tolerate contamination.

The remote filter is installed threads down on the M35A3, which means it must be installed dry to prevent contamination. You have to crank the engine to prime the system.

Clever huh!

Cat Man

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Also there is some switch (I forget where) around the fuel tank that can shut off fuel. Can't find the reference to it but I will keep looking.

I am in the excavating business and have always filled the filters on all my trucks and equipment when installing new filters.

Bet you won't on the 3116!

I found the thread on the fuel tank issue:

http://www.steelsoldiers.com/deuce/66651-problematic-m35a3-fuel-tank-check-valve.html

Couldn't start my nicest A3 today... wasn't getting fuel.

From previous experience I pulled the check valve on the top of the fuel tank
(Item 24, Fig 30, TM9-2320-386-24p, page 0031-00) and found the brass plunger gunked up badly, and the O ring a bit mangled. Cleaned and reinstalled it and the truck started in seconds.

This is the third A3 that's failed to start for me until that check valve was removed. I see on some of my trucks that it's been removed previously. Seems to be a common problem.

A couple questions:

1. Who has spares of this part?
2. Is there a better alternative? I think a check valve is somewhat important because the A3 doesn't have an in-tank pump.... just a lift pump that sucks fuel up out of the tank. The valve prevents that fuel from draining back on shutoff. Don't know what problems draining would cause.
3. Does anybody know the dimensions of the O ring in that check valve? It doesn't match any O ring in my GI O ring selections.

Bottom line for all A3 owners is that this check valve is a failry common problem with an A3, although not horribly difficult to cure when you get it clean enough to see the clip holding the check in it's body.

Thanks much.

Mark

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Your right there...

thanks Ace I will check that.

Might have been a bit over torqued. Did you drain your fuel air separator? That usually removed pressure on the fuel filter. There is a filter in the tank if I read it correctly, more of a screen really. Also check your fuel shutoff switch, see if a wire is loose. That's my quick 2 cents.

Thanks,Ill check that also.

When I picked up my -a3 from GL, I did a complete by-the-book PM and motor stables, pulling all the drain plugs to check for "other materials" and draining fuel from the fuel/water separater. I did not change any of the filters, as the fluids really appeared 'cherry'.

About 1100 miles after picking my -a3 up from GL, all the sudden she decided not to run over about 1900 RPM. Pulled the Cat fuel filter off and put on a new Cat filter. (Was very hard to take off the old one - bent the filter getting it off.) With new one on, I turned on the power switch (battery/accessory) and left it on for about 30 seconds. Then turned the engine start switch and it was immediately running.

I later cut apart the take off fuel filter, and all the element was coated in a layer of greasy slime. No wonder it was fuel starved.

My understanding is that the -3 return fuel line circulates a much greater volume of fuel than does the other M35 series. My Cat guy says that the fuel tank is now probably pretty clean....
Have driven it another 2000 miles with not a hint of fuel problems.

...anyway - just my experience...! Mark

M35A3 Fuel Problem

The Cat 3116 engine does not have an "injection pump". It has 6 individual unit injectors under the valve cover.

The mechanical governor is the thingy that looks like a pump on the left front corner of the engine. It also contains the the fuel transfer pump. Were the fuel supply line enters the transfer pump on the forward side of the governor, there is a fitting and behind the fitting there is an inline washable coarse screen that can be removed, cleaned and reinstalled. This is before the main fuel filiter.

These A3 trucks have sat idle for months and even years. Running a few tanks of fuel thru them now seems to flush accumulated junk out of the system.

Have you ever noticed that the diesel fuel pump at the truck stop always has dark brown brown varnish all over the side of it were the pump nozzle dribbles a little? Same thing is happening inside the tank and lines in your truck when it sets for a long time. Varnish!

And the comment about "I've always filled the fuel filters in my fleet" is often repeated. I learned the same thing from the "old guys" when I started many years ago. And you may get away with it for a long time, but sooner or later with the tolerences in new systems, you'll see the effect. It may not be a sudden and dramatic fuel component failure but you won't see the maximium component life you should. Under an electron microscope you can really see and compare the damage on injector plungers. Cost per hour and life to overhaul is huge on rigs that run 24/7. And when they don't last, someone always blames the engine. I've been in those customer meetings! Yikes. Just keep it clean.

Cat Man

What causes some fuel problems is the army went to JP-8 fuel to replace diesel fuel. If the truck had been running on diesel fuel and later fueled with JP-8 then the slime that grows inside the tank starts to break loose and into the fuel line it goes. Thus, having to change filters several times until it goes away. I had to change mine 4 times before the truck began to run good.

When you drain the fuel / air separator, it is common that the drain is plugged up. Open the petcock and use a piece of welding rod, etc. to clear the drain. Mine was full of **it and I had to keep poking it free to clear it. Leave the pump running while clearing it, but be prepared for a bath in diesel fuel if you aren't careful.

I also agree about the idiocy of inverting the filter. Mine was so tight when I removed it that I was afraid I was going to destroy the mounting. I'm not sure if it was overtightened or just that the gasket sticks. When my filter broke loose, I could unscrew it by hand.

I understand the rationale for placement of the filter by Cat.

Agree with glcaines on two accounts: When the filter broke free from being on tight, I too easily removed it by hand - and the new one went on easily...

I too was drenched in fuel when clearing the fuel separator - when the switch is on it comes out under a lot of pressure!!!

Mark

I solved the problem,I think.Algae in the fuel,changed the filters again and added stuff to kill the algae,Seems to run fine.