M923 nhc250 replaced injector pump still no joy!

[Over]

I have a M923A0 that I used to haul water. Slowly last year it needed a bump in throttle to keep idling at lights. It slowly got worse then I parked it. This year I pulled the fuel filter which had crap in it. Cleaned it all up, new filter, new line from tank to injector pump but still wouldn't start. Would only run on starter fluid. Pressurized tank and got good flow to pump and no leaks. Unhooked pump outlet injector line and noticed just a oozing of diesel out of it when starting. Also checked shutoff valve. Finally figured maybe the pump is bad as even when starting on fluid just an ooze of diesel on the injector pump outlet. Well...I pulled a pump from another known good runner M923A0 I have and installed it. Primed good, pressurized no leaks and flow out of large return line. Still wont start!!!!! Any thoughts?

 

[Over]

I have a M923A0 that I used to haul water. Slowly last year it needed a bump in throttle to keep idling at lights. It slowly got worse then I parked it. This year I pulled the fuel filter which had crap in it. Cleaned it all up, new filter, new line from tank to injector pump but still wouldn't start. Would only run on starter fluid. Pressurized tank and got good flow to pump and no leaks. Unhooked pump outlet injector line and noticed just a oozing of diesel out of it when starting. Also checked shutoff valve. Finally figured maybe the pump is bad as even when starting on fluid just an ooze of diesel on the injector pump outlet. Well...I pulled a pump from another known good runner M923A0 I have and installed it. Primed good, pressurized no leaks and flow out of large return line. Still wont start!!!!! Any thoughts?

I also noted when I pulled the pump that the shaft on the air compressor rotated when starting.

 

[simp5782]

Did you screw the knob in on the front of the solenoid and see if it would start? I take it that you used the shutoff valve from the other truck when you swapped the pumps.
Did you ensure you have 24v to the fuel solenoid? Is your manual shut off valve in good shape? Sometimes they can get weak internally and close on their own when fuel goes by them it is kind of like a flutter.

It takes a good bit of ether on these trucks to get them back running even with a new pump being installed.

 

[Over]

Hi..Like your videos by the way. I used your PT pump install for reference! No I have the other pumps shutoff which is good. I just stepped back in after pulling the line on top and in turning over it bubbled up maybe 1" so diesel is getting to the line. Whats an easy way to check that its making it to the injectors, I noticed a line in front of the head but it was tight but a 1/2" wrench didn't wrap around it tight.

 

[simp5782]

about the only way is to take that line off. If you have a line wrench it is pretty easy. a regular wrench will just round it off especially if it is rusted up. It is a metal line so i wouldnt think that it has anything wrong with it.

You can tell on the return fuel is to take the line off of the return valve that is below the front runner on the intake manifold. It will be a little round cylinder there with a line going in at the top and coming out at the bottom. Pull it off before the valve and see if you have fuel coming out. If there is fuel going in then the injectors should fire unless they just gave out or you broke something in the valve train. Rounding all the cam lobes off sounds unlikely so that no injectors would fire.

 

[sandcobra164]

The only reliable way I know to ensure it's making it to the injectors would be to remove the return line. There are two steel lines going into the front cylinder head, trace the lower one back to a T-fitting just below the intake manifold. Disconnect the left line and crank away to see if you have fuel. Honestly though if you have fuel at that line, you should have a running truck. Did you fill the fuel filter can prior to re-installing? The PT pump is fairly good as self priming but it cannot easily do so if the cannister is empty. I learned that my priming pump was defective when changing my fuel filter once. Turned over and over and never fired. Filled the cannister, reinstalled and it started within a minute. I also replaced my injection pump once. It started within a minute as I had not disturbed the fuel filter and the cannister was full.

 

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Hi...Went out and loosened that line and started with starter fluid. It wet the side of the motor, no soldier B to film. Went thru another can trying to start, no go. Could all 6 of the injector took a dump from sitting a year? Never heard of that but I'm stumped.
The filter canister is full and fuel runs to the pump line when pressurized. I just don't want to keep throwing cans of starter fluid at it. It ran when parked, though really crappy due to the crap on the fuel filter I figured. Everything is clean and sealed now?
I saw the air compressor shaft spinning when I pulled the pump and turned it over, also when attempting to start it builds air.

 

[simp5782]

unlikely with either non top or top stop injectors.

Is does have 24v power to the fuel solenoid correct? Not just that fuel is coming out of it. It can let a little by even when not powered. I mean the O rings on the injectors could be sucking air and not letting it do anything since it is just sucking air.

One thing I can suggest to make it easier to get going is to build a fire under it or plug the block heater in to get it warm. I know its not too cool there but it will help.

Most trucks I work on it bleeds and fires in a matter of a few turns of the motor.

 

[Over]

Yes it has power to the solenoid, plus it's the same as when I pulled it of the other truck that ran fine. I'm freakin stumped. I'm going to run a continuous pressure on the tank and try starting that way. Should rule out air leaks even though when pressurized I see no leaks. So far 3 days of replacing and going thru everything on this and it's driving me crazy! It's the Marine truck, lol!

Just in case I screwed in the combat mode screw on the solenoid.

Went out to start with 10-20 lbs pressure in tank, nothing!

Question: Is it possible the shaft from the air compressor is slipping internally or is it a solid connection? Also what pounds pressure should come out the IP pump, I understand 25 lbs at turnover? That's the next thing to check but honestly this is a pump off a running truck?

What are the other solenoids on the pump. One on top and a bigger one on the bottom. Could electrical in these case a problem?

 

[farmerboywyotech]

So just an fyi. Easy on the starting fluid. I've had more than one diesel engine apart that had been overdone. Breaks rings like its its job.

Sent from my SM-G892A using Tapatalk

 

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So just an fyi. Easy on the starting fluid. I've had more than one diesel engine apart that had been overdone. Breaks rings like its its job.

Sent from my SM-G892A using Tapatalk

Yeah that's what I'm afraid of. Have a pile of cans laying around empty at this point.

 

[simp5782]

Build a fire under it and get it warm. Reprime it. And go from there. Get that motor hot. More than likely you have some injector orings that are sucking air.

 

[Over]

Time to call it quits tonight, tomorrow starts another work week. Thanks for the help! Will throw a pressure gauge on the pump next before diving into injector problems. Thanks Again!!!

 

[WillWagner]

Injector o rings can't suck air, they CAN get hard and flat, shunting the fuel from supply directly to return. Supply is the bottom, return is the top for the hard lines going to the heads. Get a line and go directly from the pump to a can of clean fuel, clear line is best so you can see if the go juice is moving. There is no pressure on a PT pump when cranking or at low engine speed, only flow, you can't measure it unless you have a flow machine. If there is no fuel moving up the line, there is an issue with the pump, or, rarely, injectors. If that is the case, sometimes the return line can be pinched off and the engine will fire, but barely run. If it fires, there is an issue BEFORE the engine.

If the starting juice doesn't break rings, it WILL turn the built up carbon to a fluid and stick the rings so there is not enough compression to fire.

Also, if the engine is flat azz worn out, I have seen a no start until the engine temp is brought up, like Simp says, enough to help seal the cylinder enough to fire. Only seen that 2 times.

 

[WillWagner]

I should point out that if the return is pinched off/plugged and there isn't an injector issue, and the engine lights, the RPM will start at an idle speed and fairly quickly increase to a very high RPM. This is happening because the return has no place to go and the engine is being force fed more fuel, at an un regulated/metered rate due to the plugged return. If the shut off is pulled or keyed off, the engine will continue to run until the pressure is gone from the return. IIRC, max return line pressure is 2 psi, even at that, the e ngine willl idle high and loaded it will have WAY more power than it is supposed to and smoke like a freight train.

Pinching off the return was a "trick" used by truckers back when this engine was used OTR to make more power climbing hills.

 

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Hi..Sorry just saw the reply. For some reason SS isn't notifying me of reply's.

Anyhow been screwing with this issue for a couple of weekends. I put a fuel pressure gauge on the pump above the solenoid and when hit with starter fluid it read 40 lbs. Fuel is flowing as I disconnected the fuel return line after the return valve and fuel was flowing. It occurred to me that if the return valve is just letting it flow thru how does the injectors get pressurized fuel? Sholdnt the return valve somehow allow the fuel to gain pressure? It almost acts like it wants to start but doesn't fire.
Should I pinch the rubber return line with vise grips to verify?

Also before I pulled the large fuel assembly and let it sit a year it was running ok but got progressively more sluggish till I had to pull the throttle out bit by bit to keep stalling at a light. Again I'm wondering if the return valve is faulty and just letting fuel free flow thru it?

 

[sandcobra164]

https://www.youtube.com/watch?v=KzuwdxEJfQA I'm not sure why your truck is not running if you have 40 psi while cranking. Maybe the injectors are junk. Please watch this video to understand the basics of the PT Fuel Injection system.

 

[Over]

https://www.youtube.com/watch?v=KzuwdxEJfQA I'm not sure why your truck is not running if you have 40 psi while cranking. Maybe the injectors are junk. Please watch this video to understand the basics of the PT Fuel Injection system.

Great video that I watched early on in December. Always good to know the basics.
Just pinched the return line and it tried, no fire but could smell diesel smoke. Batts are low so will try tomorrow. It's a mystery to me as I find it hard that all injectors went bad from sitting. I did have the big fuel filter housing off for 6 month's then got back to it and cleaned it out and put a new filter and hose from it to the pump. Have pressurized the tank, no leaks and pump has pressure. Also in the previous post I mentioned I pulled a pump off a running truck.

 

[WillWagner]

There should be no measurable fuel pressure when cranking or at idle. The only way to get that is to install an orificed test fitting on the outlet of the pump causing the pump to see a demand for fuel. This bothered me enough to call a guy I worked with that did nothing but pumps for 22 of the 41 years he worked at Cummins. No pressure, only flow. So, there is either a direct orificed shunt to return or messed up injectors.

I didn't see in past posts, did you remove the return line from the heads to see what your return flow is? It should kinda slowly run out, not be under pressure or be flowing like 2 gallons a minute.

 

[Over]

There should be no measurable fuel pressure when cranking or at idle. The only way to get that is to install an orificed test fitting on the outlet of the pump causing the pump to see a demand for fuel. This bothered me enough to call a guy I worked with that did nothing but pumps for 22 of the 41 years he worked at Cummins. No pressure, only flow. So, there is either a direct orificed shunt to return or messed up injectors. I didn't see in past posts, did you remove the return line from the heads to see what your return flow is? It should kinda slowly run out, not be under pressure or be flowing like 2 gallons a minute.

Hi...I checked the line before and after the fuel bypass valve. Tried at the head but couldn't get even the line wrench in there. So went downstream on the same steel line and disconnected at the bypass. Should be same result. I got a mild dribble out of there. This is baffling me but these trucks tend to become voodoo sometimes.