NHC250 Cummins fuel rail pressure

[jimk]

I turned up my M813 PT pump a second time (1-1/4 total). I have a fuel press gauge on this unused plug (see arrow). I'm getting only 50psi when I go wot to 2100, no load. When I get to 2100 it drops quickly to 10psi. I must be doing something wrong.

Can the recommended 172-178 psi rail pressure be tested here?
Is it supposed to checked under full load?


TM 9-2320-260-34-1, sec 5-25

 

[WillWagner]

Yup check it there. The engine hasn't been turboed, correct? Also, it's backward. out increases, in decreases.

 

[jimk]

No, it has a turbo. Makes 16psi at 2000rpm (6psi under no load/test conditions). It runs low EGT so it can take more fuel.

I have been turning the screw counter clockwise.

Starts and runs nice. I find it hard to believe it can run nice on the 10psi indicated (or 5.8% of normal). The gauge is new. Can you suggest another diagnostic step to sort this out? Thanks


ps I think I might like a 1700% increase in power

 

[R Racing]

What are you adjusting to turn up the fuel ?

 

[jimk]

The screw behind the hole in throttle shaft (after the metal ball is removed)

I should point out, as will Wagner states above, that the directions below are wrong (clockwise should be counter clockwise)

 

[R Racing]

Thats what I thought . But My ball is missing and my screw wont turn in or out ?? That sounds perverted lmbo

 

[jimk]

Dude, you've got more problems than I do. At the risk of getting banned, my screw is off to one side in the hole and was fairly hard to turn.

 

[supermechanic]

If the fuel pressure didn't drop at high idle, the engine rpm would continue to climb until it grenaded itself.

 

[augiedoggy]

Jimk is that the rev limiter you are seeing in action?
I'll be watching this thread and trying to learn

 

[jimk]

I dunno. I'm still not sure how to test the rail pressure. Maybe it has to be done on the test stand.

I plan to change the button next. Lance R sent me this link. AWOL member Joethemechanic's interesting post #5.

http://www.steelsoldiers.com/5-ton-up/12861-m818-questions-new-member.html

 

[Floridianson]

Fuel pressure is not controled by that screw but the restrictor plate that must be changed out. Does your PT have a AF screw to.

 

[jimk]

That's helpful.

What is this restrictor plate?
What can be done with it?
What is an AF screw?
What is that throttle shaft screw used for?


I'm still at a loss for determining if my fuel pressure is off. 50psi is a long way from 170. Do I look at the gauge while I drive it?

 

[jimk]

Jimk is that the rev limiter you are seeing in action?...

I think not. The no load governed speed is supposed to be 2400rpm. Under load it's currently 2200, though I have only gone that high a couple times to check it. I think the pressure drop is the response to me backing off the throttle so I don't get to many rpms.

I'll be watching this thread and trying to learn

Me too

 

[WillWagner]

If it has an AFC pump, snap rail will only be 70 to 100 psi. To check loaded rail pressure, it needs to be loaded...on the dyno or a test stand. Test stand will be apx 10 to 30 psi lower than loaded rail pressure...dunno why, it jjust is. Maybe 'cause the stand drives the pump instead of the engine driving it? If you want to see full rail pressure w/o loading, take the AFC line off the intake, put regulated pressure to the line going into the pump...about 30 PSI and snap the gas. It should be very close to rail pressure specs...5 to 10 PSI won't matter. Maybe I missed something. Did you say it had low power? f so, the bellows in the pump could be junk. If the bellows rips or gets a hole in it, you will only see 30 to 70 pounds of rail pressure on a dyno or regulated pressure test. 30 to 70 is no air fuel pressuer. Designed to get you off the road. Another thought, did you just turbo it?

"Fuel pressure is not controled by that screw but the restrictor plate that must be changed out. Does your PT have a AF screw to. "

?? Maybe you are thinking about a Bosch system and the rack stop plate? PT systems have no plates, it's all done with springs, fly weights and manifold perssure if equipped.

 

[jimk]

Power is good.

Yes it is turbocharged. Why is that important? I have low EGT and want to increase the power, maybe 10-20%. If I add fuel the boost, charge air temp and EGT will all go up. I feel it can easily tolerate another 200*F.

TM 9-2320-260-34-1 page 5-1 said I have a PT and AFC plugged. I'm pretty sure there is no line to manifold. If I knew where the plug was I could add the 30psi.

Is that bellows the same as the pulsation damper (in illustration post 12)?

I'll move port gage to cab, drop the button 5 sizes and report back. Tally-ho.

 

[jwaller]

will, he added the turbo like I did and I don't think he has the AFC line, it was a stock 250 and pump.

 

[WillWagner]

Power is good.

TM 9-2320-260-34-1 page 5-1 said I have a PT and AFC plugged. I'm pretty sure there is no line to manifold. If I knew where the plug was I could add the 30psi.

Is that bellows the same as the pulsation damper (in illustration post 12)?

I'll move port gage to cab, drop the button 5 sizes and report back. Tally-ho.

Your pump doesn't have a bellows. Not the same as the damper, that's there to take the pulsations out of the pressurized fuel that the gear pump makes.
It could be that it's just the way the pump was set up that you are seeing all the rail the pump will make. The button is the right way to do it any way. Be careful, lots of spring tension in the gov. pack! Don't lose any shims!

 

[Floridianson]

Will when we add a turbo to a noturbo motor should the PT be changed out to one with AF screw and reset up by the injection shop?

 

[WillWagner]

All the AFC and bellows is for is acel. smoke. If you don't care about black smoke when leaving a light, nope.

 

[jimk]

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