M54 LDT-465 dies out. Lifter pump problem?

[msisco]

Hi All,

Looking for ideas on what might be the problem. The LDT-465 dies at random while driving and I think it might be the lift pump/fuel pump (in tank). I just bought the truck and done the following to trouble shoot:

Cleaned the primary fuel filter. (It looked ok and seems serviceable, plus I could not locate a replacement)
Replaced the secondary fuel filters.
Replaced the air filter.
Dumped the old fuel and put in 25 new gallons of diesel.
Primed the fuel at each filter one at a time and finally at the last fuel injector.

It runs and starts good but seems to lug a bit at times. The performance is ok in general other than it does seem to lack power at times.

The fuel pump or lifter pump in the tank seems to loose prime and then the truck dies. After I tun the power on and off serveral times the pump seems to reprime. You can actually hear a big change in the sound of the pump when it primes. The sound goes from a loud high reving whine to a quiet fluttering sound and you can actual her fuel moving. Once it gains prime the truck will start right up. It usually will run a few miles or minutes and die out again. I usually have to turn the power off and on 3 to 10 times before it primes or catches again and will start.

I took the tamper proof screws off the fuel pump head/screw but can not seem to take the pump a part any further to investigate. The pump head has those flat blade screws that you can only tighten. I guess it's not a serviceable part hence the tamper proof screws?

What do you think? Do I just need a new intank pump? Where is a good place to get one if that is that case. I can't wait to get on the road again!

 

[wsucougarx]

Maybe a good time to hook up a pressure gauge to the fuel line to see what the intank pump is getting your pressures upto. Typically a deuce MF will run with an inop intank pump, just as long as you don't need to bleed the fuel lines. The IP has enough suction to draw fuel to keep the truck going. I am a bit concerned your truck is cutting out while driving. Have you had a chance to blow out your fuel lines? Wondering if you have some gunk in there obstruction your fuel flow. Did you drain your fuel tank? Notice any algae or other gunk? Does your truck have a smooth idle? Do you hear any misses? Does your truck smoke excessively regardless of operating tempature? Notice any excessive vibrations during idle? Have any diesel fuel leaks in your fuel lines? Just wondering if you're getting air in your fuel lines. Is your fuel shutoff valve going all the way in when you push in the in cab handle?

 

[msisco]

The truck is two hours from my house now. I didn't have a pressure tester with me yesterday. Now it's another week or two before I get back to continue the trouble shoot.

I did not blow out the fuel lines. I can try that next.

When I first primed the system after the tank dump and filter change there was plenty of fuel flow all the way to the last seconday fuel fiter. That was when the pump seemed to be primed based upon the way it sounded. I did disconnect the power to the fuel pump after the engine was running and it ran for a few minutes before it died. Question: would an LDT-465 with a LDS-465 Injection pump need the lifter pump running at all times? Does the IP have enough suction to keep up with the demand without the lifter pump running?

 

[wsucougarx]

Hmm now I'm really wondering about the fuel lines and IP. These trucks are designed to run without batteries (combat situation), therefore no intank pump working. The IP is suppose to draw enough fuel to keep the engine going. When the batteries are in the truck the in tank pump does work continuously regardless of fuel line pressure.

 

[emr]

gee, thats a tough one, I had a motor that would run all day at the shop at 2500 rpm and when I went down the road and hit third gear it would shut down, had a guage on everything all was fine, checked for hot spots, none, went thru 4 injection pumps, everyone said it is the injection pump, i have had multiple bad parts in my life before so i kept changing them, finally pulled the motor and swapped it out, and it sits at my shop, if it does not get junked first i will pull the head and look inside, man it was a mind blower, hope u have a simple fix, good luck...

 

[Stretch44875]

You can swap any part between a LDS and LDT motor, and run it. Pump settings are different. But the LDS pump will work fine on a LDT motor. Bellhousings and starter locations are different, depending on what truck it is in, 5 ton or 2.5 ton.

If the fuel system has no air getting in, the truck will start and run without the intank pump working.

 

[gimpyrobb]

I would say the filters are suspect. I know I have had my motor die out when my filters get clogged. Find a new filter before you go any further.

 

[msisco]

How about that lifter pump? It for sure seems to have a priming issue. One out of 10 times I turn on the main power the pump sounds right and will run fine. The other 9 times the pump sounds like it is running dry. As soon as it catches and primes the truck fire up right away. Since the pump runs as long as the main power is on I wonder if it could actually be causing the fuel loss even though I understand you dont need the lifter pump running after the system is primed. I am looking for a new intank pump unless I can figure out how to rebuild the one I have. Anyone ever rebuilt the pump before? The pump motor always spins so I don't think that is the issue. Any leads on a new pump assembly? I've been looking and only found a used take out so far.

Thanks guys!

Mike

 

[Earth]

Change the first filter! Motor dieing out when running means lack of fuel more often than not.

Once the truck starts the only thing important that the lift pump could be doing is compensating for an air leak or helping push fuel through a bad filter so the IP can pull it home.

 

[gimpyrobb]

Another issue (don't you love to hear that) is the pump can sound like its working, but the bottom screen could have fallen off. If you have not had the in-tank pump out, I would pull it and make sure all is well. Most of the pumps I have pulled, have benefited from having the screens around the impeller cleaned with a wire brush.

 

[Warthog]

I'm with Gimp, I would pull the tank pump for an inspection/cleaning. While you are in there also check the rubber fuel lines. I have had a truck that the line had a crack in it and wouldn't pump correctly.

Section 3-26 of the TM 9-2320-361-20 manual cover how to test the pump pressure and perform maintenance on the pump.

And then work your way from the tank to the IP checking for leaks.