NHC250 Cummins fuel rail pressure

Hey Jimk any results on the buttuns that you used? I have turboed my truck and havent touched the fuel yet but i want to i am not getting any smoke what so ever and egts are so low. I had a guy to tell me that i couldn't get the engine with the stock pump and injectors and that it wouldn;t ever get enough fuel to do that.

Thanks for asking. Installed button #20. Easy job thru the starter access panel. Seems stronger, better thru mid range... Makes about 2psi more at higher rpm, maybe 18psi at redline. Not much smoke. Probably could have done #17.

Fuel rail pressure is 225psi at WOT at 2100rpm. EGT seems about the same as before. Haven't seen it go over 700 (post turbo). I have a 200mile tow Sunday. Should know more afterwards.

Right now the rpm come down very slowly. I'm hoping it is just air trapped in the long fuel hose (to cab gauge). Might be acting like a fuel spring? Gauge is close to zero while rpm is still coming down (slowly).I'll remove the gauge tomorrow and re-plug the pump.

Still looking to recalibrae my pump to one that was for a 290. does any one have the numbers from a 290 pump that runs close to the 250. I have talked to guys at cummins and they said there was different pumps that were used on 290's. Just wondering what i need to get my pump calibrated for.

Do believe most of our pumps should be 172lb and you are still safe at 180lb but my Injection man did not want to go any higher.

any photos of the buttom replacement?

Vinny

Any udates on this

I am using the #20 button. Never tried my 17. The slow-to-return-to-idle was indeed the gauge, specifically the air in the line to cab. The air would compress as fuel pressure builds then expand when you get out of the throttle, pushing extra fuel into the injectors. The issue went away after I removed the gauge after a few days of study. Manifold pressure max is 19-20psi at 2100.

Anybody know how high the EGTs will go above normal when you drop 5, 7, 10 button numbers in a NON-tuboed 250., I am pulling the IP because the input seal is now leaking like a open faucet, so If I am going to bump the IP a bit to help on lonnnnnnnnnnnnng hills and also to make MORE smoke (yes, I said more SMOKE, I like the steam engine look), NOW is the time to do it.

There is nothing like a diesel engine blowing smoke under load to say POWER, even if it is only an illusion

Any suggestions on HOW to get the drive OFF the input shaft of a AFC ip so I can pull the cover to replace the seals, a few HINTS sure would help, Thanks

73m819 said:

Anybody know how high the EGTs will go above normal when you drop 5, 7, 10 button numbers in a NON-tuboed 250., I am pulling the IP because the input seal is now leaking like a open faucet, so If I am going to bump the IP a bit to help on lonnnnnnnnnnnnng hills and also to make MORE smoke (yes, I said more SMOKE, I like the steam engine look), NOW is the time to do it.

There is nothing like a diesel engine blowing smoke under load to say POWER, even if it is only an illusion

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Ron, it's anyone's guess as to how high your EGTs will be. Best advice is to install a EGT gauge.

jimk said:

Progress report- Here are some pictures of the button and associated parts. There is a small washer (not shown) in the cyl. for the end of the small spring. My button is a 27. It is the correct ones according to the calibration code on tag on the top of pump. The local Cummins dealer had some trouble figuring out what I was talking about. The part is known as an Idle Plunger. Here are some button #'s. Cost is $12.30/ea. They will be shipped from the factory. I'll try the #20 then edit, update this post and bump. Should be about 2 weeks.

button #17 - part #140417
button #20 - part #141629
button #22 - part #141630

Does anyone know what button a stock NTC290 and/or NTC300 uses? Or, if someone can provide a calibration code from a pump the dealer should be able to tell me.

Boost and EGT update to follow

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JimK: I was really glad I found this thread today. My PT pump on my 350 was leaking so bad (throttle shaft) after a little while last year that I decided to put the pump from my 250 onto it and in theory get the problem resolved a little cheaper then say sending the pump in to have it rebuilt. My local cummins guy said it would work with a bit more response than the pump originally on the 350 as he claimed it would have a tad bit more fuel pressure supplied to the injectors. (don't know why but thats what I was told) Anyway, to make a long story short, the new pump installed, I fired it up and got poor response, cracking, and poor engine performance. It wasn't idling down right in order for me to shift properly through the rpms and in general was making me think that after the long winter I had a froze up valve (it was my first start of the season) After finding this thread I got to thinking maybe I'd try switching the plunger from the 350 pump into the 250 pump currently installed on the truck. I switched the plunger, the button, springs and stack of washers. fired right up and sure as heck that truck came to life!!!!!! no excess smoke, no hard starting, and wow!!! did it make a difference on the test run on the road. I read somewhere that to make those Cummins come to life one of the improvements that Cummins did was to supply fuel to both ends of the rail simultaneously but at the same time with a bit less fuel pressure as the #6 injector was no longer getting what was left over after injectors 1-5 took their supply from the rail. Now the supply to the rail is equalized, and bit higher pressure I believe and none of the symptoms I described earlier. High end rpms still the same and low end idle rpm is the same only smoother running, with no loping. The PT pump from the 350 was equipped with a bellows where as the pump currently installed from the 250 did not have one, but I don't think that there is a need for a bellows as the supply of fuel is under a bit more pressure anyway. I wish I could give you guys a few test pressure numbers and etc, but I'm sort of flying by the seat of my pants here on this one.

grunex125 said:

but I'm sort of flying by the seat of my pants here on this one.

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Me too.

So do you remember what the number the 350 button was?

I looked at that rear fuel rail port... If I remember correctly I thought it was a tough access due to the firewall being too close. For me it was more trouble than it was worth (dual feed). Then I have been know to be lazy. You'd think adding some psi might accomplish the same thing. I dunno.

I always think a bit of air might get stuck at the end of the rail because it still comes down slower that I like. That dual feed would make sure there is no air back there. Not much room for air the way it is. Probably just the heavy flywheel. If it acted like a chainsaw I'd probably stall it at every light. The air in my test gauge made take a long time, like 5-10 sec., to come down from 2100. That was with a 6-8ft hose/ fuel line and a small, temporary, gauge near windshield.

If you had a probe in each exhaust manifold port and multiple egt gauges (or one gauge and a 6 pole switch) you'd know indirectly the vol of fuel is going thru each injector. If it is low at end of rail the rear cyl would be cooler.

I looked at the button but did not see a number on it, I just knew that I needed to be exchanging exact parts to get the same performance. The stack of washers on the back side of the plunger (or front depending on which way you look at it) totaled eight washers from the 350 and the 250 only had six. I didn't have a way to measure spring tension(force) so I again opted to switch the spring as well. As for the dual line feed, the 350 already had that when I put it in the truck, so trying to get the line in there was not an issue. Only thing was being extra carefull on that end as I tilted and set the new engine down on the rear mounts. Since I used the stock bellhousing and trans, there was no problem locating the rear portion of the engine in relation to the drive shaft and firewall.
I know what you mean when you say about the length of the hose. It's pretty hard to install a guage or set of guages to monitor preformance when you have to put the hood down for your test drive. reomote readings as you described is about the best a person can get in this case but it worked out alright in the end from what I gather.
I'll have to look and see if I even have ports for egt probes, this sized engine is still rather new to me yet so I still have lots to learn about it. Where would I be looking if there was any ports? Most of my experience with diesels comes from 7.3 fords, 478 Herc's and 6bta Cummins engines so it is a bit of a change working with Pt pumps, and top stop injectors.

grunex125 said:

Where would I be looking if there was any ports?

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The drill and tap kind.

jimk said:

The drill and tap kind.

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IC.hmmmmmmmmmm well I guess that rules that out for now...lol

I will bump this back to the top with some information

The pump I had one my NHC250 and ran for ever was a #16 button with 170 rail pressure. It ran hard and pulled well with little smoke. Would probably be a little bit of underpower for a turbo truck with a load on it. However it would run a NTC-400 at idle and on upwards with no load.

This is a fuel rail test on my NTC-400 with the flow screw maxed out and a #15 button. Set right at 200 on rail pressure when I am on it and about 40/45psi running 60 with slight throttle. This was a slight mod we did to the pump today.

https://youtu.be/K-f8GHWCq0c