M923A1 Fuel problem... Won't start!

I have a M923A1 that is a 2010 rebuild. It started having fuel problems awhile ago where it would chug and spit and no power until it got warmed up. Once warmed up it ran fine. I don't drive the truck much... But this went on for several months. Then I went out to move it, and it it started, but didn't run long enough to warm up and it died.. and wouldn't start again. It will start on starter fluid, but won't stay running. So far I've:

- Drained the fuel tank and cleaned it, added fresh diesel.
- New Fuel filter, cleaned the housing, w/ new O-rings
- New PT pump filter screen
- Primed the system
- Checked that fuel is coming out of the fuel line at the motor while cranking

I saw one post saying that they had a stuck return line check valve... and my engine doesn't have one? I've traced the return line from the motor to the tank, and there isn't a check valve, unless it's inside the tank??

Can anyone offer any other ideas where to look now? HELP!!!! lol

So you have fuel at the engine side of the pump. Have you cracked an injector to check for fuel. Check the emergency kill linkage?

are you gretting fuel returned?

big block 88 said:

So you have fuel at the engine side of the pump. Have you cracked an injector to check for fuel. Check the emergency kill linkage?

are you gretting fuel returned?

Click to expand...

- Yes I am getting fuel out of the fuel line attached to the front of the block when I crank the engine. It pulses out at a decent rate.
- How do I crack an injector to check for fuel?
- Yep, I checked the emergency shut-off cable and manually pushed the linkage on the shut off valve on the engine to be sure.

I'm definitely not a diesel mechanic by any means... lol

You can't crack the injector on a 250.

Your return valve is the little cylinder thing hiding up below your intake on the front runner. return line comes into the top of it and exits out the bottom then it goes to another T then back to the tank and return to the pump. It is a little black round thing.

Replace your metal feed like from the pump with a pushlok type hose and fittings into your filter housing. If your feed from your filter to your pump is cracked, get rid of it and replace it.

Yeah.... thinkin a2 for some reason i apologize. I meant no offense to your 250 by calling it a school bus motor 8.3.

If you are getting fuel on the out side of the ip then id check for return flow.

Have you given it any ether to give it motivation to start? Sometimes it just takes a little bit to get em going to work what little air they have in the lines out. a 250 will run with air in the system but the ether will motivate it to clear the system.

He said it will start on fluid but not stay running. I wonder how hard hes forcing her to run. I know a lot of people dont like to but i will flat foot that pig till you hear it firing diesel. It smokes and clatters and clunks but once you hear and feel it on diesel it should stay running.

The thing that stands out to me is that it was running then stalled out and now wont resart. Only time i had that on a 250 my electric fuel shut off had failed. Turned the screw all the way and it fired right up.

Cracked hose sucking air in between fuel filter outlet and injection pump inlet.

Or how much fuel is in the tank? Maybe the pickup tube has broken and fell down into the fuel tank.

Remove the fuel cap from the tank. Make sure the tank vent isn't stopped up with dirt dauber spawn of satan from ****.......

Take a coat hanger or small diameter rod and poke into vent tube that is hose clamped to your intake tube on the side of the cab.

Did you get the fuel filter oring seated and sealed correctly when you replaced the element? Can suck air there as well.

I would try to use a fuel can and hose and go right into the pump, If it runs that way then you have an air leak some place. Make sure the can and hose are clean, no filter.

Or somebody doesn’t like you and poured something in your tank.

Thanks for the ideas.... Ive been too busy to tinker with it. Once the holidays are over I'm going to try a 55gal drum of fuel plumbed directly to the PT and return line to the drum and see if it runs. If it does, I'm dropping the entire rest of the fuel system and tank and rebuilding/replacing everything. I'm going to go ahead and put an insulated tank on it too, with a 24v electric lift pump to provide positive pressure to the PT.

PT pumps are not designed for positive pressure.

doghead said:

PT pumps are not designed for positive pressure.

Click to expand...

Neither is the CP3 in a duramax... but man does a lift pump help them out. An LP has been added to a few trucks on this site. A search will show it helped.

Have you figured out your fuel problem? My truck (1986 M923A1 with non turbo 855 ci cummins) is doing the same thing you described. I removed the tank to clean and temporarily installed an electric fuel pump to a 5 gallon can and did not help at all. Having a horrible time finding someone who can help. Thanks

doghead said:

PT pumps are not designed for positive pressure.

Click to expand...

In some industrial and marine applications, supply fuel location is higher than the engine. If there is 250-300 gallons of fuel in the tank, how much pressure is on the inlet of the pump? Pittsburgh Diesel has been using a high output pump to force feed PT pumps for ages.

To the above post, did it run fine BEFORE removing components for cleaning?

On my truck, I bought it about 5 months ago and did all the normal maint which included fuel filter. It was a disaster and ran much better after the maint. After about 6-8 hours of running over 8 weeks, it started running lousy and then died and won't restart. White smoke coming out of exhaust and the engine tries to hit but won't stay running. I'm to the point of pulling the pump off and going through it. Any help would be greatly appreciated.

When you put the lift pump into the system, did you go directly to the pump or thru the entire system? Easy checks first, get a clear line and go directly from a clean bucket of fuel directly to the pump, it's ok to run for a bit with unfiltered fuel. If the pump sucks the fuel into the pump and you have a no start, turn the knurled knob in at the front of the fsov. If it is still a no start, probable pump issue, most common failure is front seals, If it will not pull fuel up the line, look into the fitting at the inlet of the pump, it is possible to have sucked up debris and have it lodge in the fitting. If no debris, something is most likely amiss in the pump.

WillWagner said:

turn the knurled knob in at the front of the fsov.

Click to expand...

I do that first when having trouble.

WillWagner said:

In some industrial and marine applications, supply fuel location is higher than the engine. If there is 250-300 gallons of fuel in the tank, how much pressure is on the inlet of the pump?...

Click to expand...

The amount of fuel is not really relevant, other than the level in the tank being higher full vs empty.
.4335 psi is the head pressure per 1’ of water, due to the lighter weight of diesel it would be a tad lower, so a tank with a fuel level 10’ above the pump inlet would be around 4.3 psi.

Will try the hose next. I'm not sure about the knurled knob on the front of the fsov. Sorry for the ignorance, but I'm brand new to the 5 tons. Thanks and will post findings.