M923 Hard to start on any slight incline

[Manstein]

If I leave it on flat ground over night it lights with just a bump of the starter, but if it's just slightly nose up, it takes forever to reprime. Can't see any visible leaks in the fuel lines. Anybody else run into something similar?

 

[rrrr]

Your loosing prime on your IP. I would think you have an air leak. Did you recently replace the fuel filter ?

 

[Manstein]

I agree on the air leak but I haven't replaced the filter. In fact, before I started just random tightening of anything, I thought I'd seek the wisdom of the hive.

 

[juanprado]

I would be very curious as to what you find as i have the same exact scenario. I took my truck to my boy scout camp and it is parked tail end down a slope , nose high, and now won't start. I am thinking the fuel level is at an angle below the pick up tube and sucked in air.

I am going back next week to it to change the filter, fill the bowl and see if I can prime it.

Please keep me posted and I will let you know next week if I am successful!

Juan

 

[engineer233]

Mine has the same problem. Level all is well, nose high it has trouble getting started. I thought my truck was low on fuel causing the problem. I had a 1/4 tank at the time. I just thought it was my truck. I'm glad to see this thread.

 

[scoutmanadam]

what fuel level are you keeping your truck at

 

[engineer233]

I generally don't like to let mine get below a 1/2 tank .

 

[D-Man]

Do you all have a fuel filter before the lift pump? Replace the filters before and after the pump.

I would also disconnect the line into the lift pump and ensure the metal screen is not clogged.

On my M939, I installed a full-size, screw-on fuel filter (not a water separator) before the lift pump and a new lift pump and have never had any priming issues since.

Keep us posted!

 

[juanprado]

Dman,

Could you post pictures of your filter set up and the lines when you get a chance? Also, can you show pictures of your lift pump?

Thanks!

 

[M35A2-AZ]

Just an FYI, but I had a priming problem in my M923A1 and it turned out to be the pickup tube in the tank.
http://www.steelsoldiers.com/5-ton-up/79327-m923a1-losing-prime.html

 

[D-Man]

Juanprado,

The line from the fuel tank comes into the fuel filter on the very left. It then goes into the lift pump in the lower center. From there, the lift pump line goes into the fuel/water separator and then to the IP.

Let us know if this helps. Good luck!

 

[juanprado]

Thanks for the Picture D- man!

It looks like you must have the 8.3 as that does not look like mine with the NHC250 but I hope it also might help someone else for a reference.

Juan

 

[D-Man]

No worries, I hope you get this figured out soon.

 

[Durango_USMC]

Dman, That is one clean looking engine!

 

[D-Man]

Durango,

Thank you. I spent a bit of time cleaning it, taping stuff off and repainting it with Cummins Beige.

A little tedious, but worthwhile.

Semper Fi

 

[juanprado]

update on M923 NHC250 no start

I have changed the fuel filter and filled the canister full of diesel. It was about 70% full previously. No sludge or nasty looking stuff present. I have added 15 gallons to the tank. I primed the pump 1000's of times but no fuel is flowing from the pump drain at the primer even though I can hear the tank gurgling and the filter is gurgling. Since I hear the airflow I believe the pump is working. Opened the top drain on the fuel filter canister and I got a drip. How do I know if the primer pump is bad?

Next step, I cracked the rubber line going to the injector pump from the filter housing and filled it with diesel to the top and screwed it back in.

Cranks but no fire. Starting fluid in the air cleaner will let it run ok for 2-4 seconds.

Do I need to keep cranking to get rid of air?

I am thinking of turning the fuel solenoid screw in. Is it regular right hand threads to bypass?

Am I missing something? Any words of wisdom are welcome?

 

[rrrr]

You still have an air leak between the pump and the tank. Did you get a good seal on the fuel filter ? With an air leak the primer is not going to work. I had to snug and twist my filter assembly a couple of times to get it to finally seal.

 

[D-Man]

Do you have a filter between the fuel tank and the pump?

Have you checked the pump screen for accumulated sediment? This may prevent it from developing enough suction even though it is gurgling.

You should not have to prime it but a dozen times or so.

I suspect your lift pump may be to blame here if you are only getting a drip and there are no air leaks.

 

[Beerslayer]

The hand primer pump on my truck does not work. At all.

When I changed my fuel filter, the only way I could get the system primed was to drill the fuel cap and install a valve stem for charging the system with air.

Usual warnings about putting too much air pressure on that tank apply.

 

[Lonekazoo]

I just recovered my first 939 series truck, an M923A1, and while it started with just a couple cranks at the GL lot, it ran really rough and occasionally made a disturbing knocking noise at idle.

During the 1000 mile drive home, it ran fairly well, but idled like crap, and at each startup it would invariably run for 5 or 6 seconds, then stall or nearly stall. And later on my trip when I started wearing my noise cancelling headset, I realized that I could also hear it missing at higher RPM's.

After arriving home and parking it on an incline, it would not start at all. I remember reading this thread so I set off to find an air leak. I went through the priming proceduces, but the pump would not lift fuel. I loosened the fuel line off of the priming pump and was about to backfill it, then I noticed the lower fitting was very loose! After tightening it down, the priming pump drew fuel in about 5 pumps. Not only does it start immediately now, but it idles smoothly and with no missing or knocking.

So it was either drawing air, or not lifting enough fuel. But at any rate it was causing a fuel delivery issue, and I'm grateful for the suggestions here. It's a whole new truck! So don't forget to check all the little fittings.

George