M923 nhc250 replaced injector pump still no joy!

What bypass fitting are you referencing? I could not see what you did in the pic with the circled things.

WillWagner said:

What bypass fitting are you referencing? I could not see what you did in the pic with the circled things.

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The bypass (Probably wrong name) would be the one valve at the end of the hard return line from the head.

Over said:

The bypass (Probably wrong name) would be the one valve at the end of the hard return line from the head.

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That is called a pressure reduction cylinder. It just slows the return flow down. You can ditch it which should be done anyway. The return line should go from the Head to a T which splits into a pump return and return to the tank.

Those cylinders are known to gunk up and cause issues. They were removed on trucks that saw engine modifications.
Go to your local hydraulic shop and get a 1/8" NPT to #4 female union. You want a #4 male JIC to # 4 male JIC 90 degree fitting. a hydraulic hose with # 4 female JICs on each end and about 36 inches long overall. You want a 1/8 NPT male to 1/8 NPT female shut off valve. and a 1/8" NPT to #4 male JIC 90. This will eliminate the metal line going to the pump. You need to ensure your feed line is good going to the engine. lAll of those fittings will replace your metal line from your IP to the front of the head.

If you have not replaced your main filter to IP feed line then you should do that as well while you are at the hydraulic shop

simp5782 said:

That is called a pressure reduction cylinder. It just slows the return flow down. You can ditch it which should be done anyway. The return line should go from the Head to a T which splits into a pump return and return to the tank.

Those cylinders are known to gunk up and cause issues. They were removed on trucks that saw engine modifications.
Go to your local hydraulic shop and get a 1/8" NPT to #4 female union. You want a #4 male JIC to # 4 male JIC 90 degree fitting. a hydraulic hose with # 4 female JICs on each end and about 36 inches long overall. You want a 1/8 NPT male to 1/8 NPT female shut off valve. and a 1/8" NPT to #4 male JIC 90. This will eliminate the metal line going to the pump. You need to ensure your feed line is good going to the engine. lAll of those fittings will replace your metal line from your IP to the front of the head.

If you have not replaced your main filter to IP feed line then you should do that as well while you are at the hydraulic shop

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Thanks for the info!! Trying to decide if it's the injectors or pump. Don't think all the injectors could go south at the same time plus when I pinched off the return line I got smoke but no fire so I think the injectors are trying. I may end up popping the injectors out to see if crap got in the screens. Trying to avoid rebuilding a PT pump that worked in the truck I pulled it from. May also just pull the supply fuel line and set it in a jug of diesel to discount down stream problems.

The direct feed with a new line is the best measure to start. You can pull the valve cover and ensure they are moving. and use a listening device to see if they are firing when the engine is spinning over.

Ahh, I see it, it is a 2 PSI check valve....no idea why it would be put there. Those are usually installed if the fuel system....tank and plumbing, are higher than the engine....cranes, boats, industrial stuff.

From all you have done and the cranking pressure, IMHO, it is toward the injector end. You already replaced a pump, correct? Yes, it is odd for all 6 injectors to fail at once, but it has happened.

simp5782 said:

The direct feed with a new line is the best measure to start. You can pull the valve cover and ensure they are moving. and use a listening device to see if they are firing when the engine is spinning over.

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Hi Wes

So I should hear the injectors clicking (firing) when the compress the diesel?

No, injection is done by the camshaft lifting a push tube, pushing up on a rocker and the rocker pushing a plunger down into the cup of the injector, no pop off like a bosch system, just the action of the plunger forcing the trapped low pressure fuel through 7 microscopic holes on the end of the cup. Simp did have a good idea, remove a valve cover and crank the engine. IF the cam broke just behind the gear, the pump would turn but no injection would happen, only seen that one time, you would not see the rockers moving if that happened. Take the return off and look at the flow or, pull an injector, and hit the plunger with the heel of your hand, if no fuel comes out, injectors are plugged. It really only takes maybe 5 mins to pull an injector

+2, you can view the rockers on the center head by removing the oil filler cap and having a friend crank the engine over. No movement while cranking means the camshaft not turning. If it was trying to fire slightly with the return line pinched, I'm think everything is turning. Not that I'm a fan of starting fluid, I'd be game to try a small spray at this point.

I think he has used a bunch so far....

WillWagner said:

I think he has used a bunch so far....

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Used more Starting Fluid than I care to think about. When the rain comes and goes I'll jump on top and check the cam then pull the injectors. 15 minute job, right?

All, a bit longer than that. I hear ya on the rain! It has been pouring here for two days. No need to pull the boxes, loosen and pull the injector adjuster, flop the lever back and then pull the hold downs and injectors....don't drop the hold down bolts down the push tube cavity!

FINALLY GOT HER GOING!!! Appreciate all the help here and special shout out to Wess and his videos! Noticed when I pinched the return line it tried but no go. Then I noticed the rubber return line was leaking at the first joint due to the hose being old and brittle. Went and set up a fuel line into the PT Pump from a gallon container, then I replaced the rubber return line and let the new one run into the container. I filled the jug with 1/2 Diesel Kleen, added a bottle of of LiquiMoly Complete Diesel System Cleaner (Couldn't find their Diesel Purge here) then added Diesel to top of the jug. First I used a clamp on the return line then gave it a go. She really tried and was so close I hit the mushroom intake with some starter fluid. Took a couple of try's then she ran under her own power. When it sped up I would loosen the clamp she would slow down then tighten again to speed up. When pushing the throttle not much happened so I just let it run, clamp, un-clamp. After a while I think the injectors started loosening up and she would respond to throttle. Finally pulled the clamp and let her run thru 2 gallons of the witches brew. Connected everything back up, primed and she started again! Woke up the next morning (40 degrees) and she smoked and tried, finally started when I just left the throttle alone and didn't mash it.
Question: Cold starting a NCH250 should I leave the throttle at rest or press it. I know my diesel 6.2 Burb doesn't like a lot of throttle on cold mornings. Again thanks to everyone here!!!!!!!!!!

Should fire at no throttle with a good fuel system. Some ether may be used if below 32 degrees

Over,

It sounds like you had two problems? A leaky return line and gummed up injectors?
For cold starts (32F and colder), my truck wants exactly what the dash data plate says- "Apply 1/3 foot throttle." It definitely does not like more than that. The warmer the temps, the less pedal it wants.

Ajax MD said:

Over,

It sounds like you had two problems? A leaky return line and gummed up injectors? For cold starts (32F and colder), my truck wants exactly what the dash data plate says- "Apply 1/3 foot throttle." It definitely does not like more than that. The warmer the temps, the less pedal it wants.

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Yes that's what I figured. My throttle pedal was sticking down a ways and seemed like to much diesel got to the cylinders so it just smoked. Throttle is sticking in that area right where you cant see it under the cab. A year sitting and I believe the diesel just gummed up on the injectors. Probably wouldn't happen on the M923A2's with their pressure injector system. The leaky return hose was a culprit in regard to when pinching the line it wouldn't let all the pressure build up to force it into the injectors. Other than that the return line should have been fine but was pretty hard and cracked. So after all the removing pumps and messing with everything I guess I could have just replaced the return line and pinched it. Gotta love the MV hobby learning curve! Now I wander out into the yard once a week starting my trucks up, good excuse for a beer!

simp5782 said:

Should fire at no throttle with a good fuel system. Some ether may be used if below 32 degrees

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Your videos are a great help! Need to go thru some I saw that addresses other issues I have on the trucks. Shortens the learning curve! Thanks again!

Heh, the reason I asked for confirmation of your solutions is to shorten my own learning curve. I'm not having any problems *yet* but it's probably only a matter of time so the more knowledge I absorb now, the less painful it'll be later...

Ajax MD said:

Heh, the reason I asked for confirmation of your solutions is to shorten my own learning curve. I'm not having any problems *yet* but it's probably only a matter of time so the more knowledge I absorb now, the less painful it'll be later...

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Understand! Wish this thread was up when my Gremlins started showing up. The world needs test dummies and I got elected to this one, lol!