Injector Pump Tuning Question

[Lonnie]

If I understand correctly the fuel button controls your fuel pressure, but the fuel screw can change the flow/pressure also... I was trying to follow the circuits, but detailed really info is hard to come by.

Am i understanding it correctly that the screw in the throttle shaft can allow more pressure to the injectors, but it is ultimately limited to what the button will give for max pressure?

Will the screw allow you to fatten up the pressure in the mid RPM better than adding a smaller # button which ultimately boosts pressure across the board?

Trying to understand how the 2 in combination work together.... if they did the exact same thing, there would only be a need for 1 adjustment.

 

[simp5782]

If I understand correctly the fuel button controls your fuel pressure, but the fuel screw can change the flow/pressure also... I was trying to follow the circuits, but detailed really info is hard to come by.

Am i understanding it correctly that the screw in the throttle shaft can allow more pressure to the injectors, but it is ultimately limited to what the button will give for max pressure?

Will the screw allow you to fatten up the pressure in the mid RPM better than adding a smaller # button which ultimately boosts pressure across the board?

Trying to understand how the 2 in combination work together.... if they did the exact same thing, there would only be a need for 1 adjustment.

Shaft screw is what controls the force pressure on the injectors. The button is what allows the rate of fuel by it. Anything above 250 rail pressure will eat a cam.

Are you running a dual fuel line? aftercooler? intercooler? fuel cooler? What size fuel line from the tank to the pump? All going to be factors in your fuel setting.

You will not want to venture below a 16 button on the SC and adjust your rail pressure vs pulling and not pulling(the boost numbers) I had mine cranked to 250 on a big cam and I didnt notice anymore difference than 225psi. I also had a large slow boosting turbo though. Could also have injectors redone by Premco that will give you increased flow which then will let you reduce rail pressure and button size.

 

[Lonnie]

Shaft screw is what controls the force pressure on the injectors. The button is what allows the rate of fuel by it. Anything above 250 rail pressure will eat a cam.

Are you running a dual fuel line? aftercooler? intercooler? fuel cooler? What size fuel line from the tank to the pump? All going to be factors in your fuel setting.
.

The screw/button relationship you stated contradicts what I was reading... I was understanding it was the opposite.
Still trying to get my thoughts sorted out.

I have no coolers at this time. Due to the small injectors in the NHC-250, I am only seeing 14-15# boost, but it doesn't max until 2000-2200 & it is lower in low gears.

A #17 button is in there, but I'm seeing 210 psi, just before it defuels, at lower speeds it varies from 150-200, then spikes just before the governor kicks in.

The turbo (a HT3B) does not make a lot of boost at 1500, maybe 7#, but EGT's are not high, so it appears I could use more fuel that will spool the turbo better.

Any ideas?

 

[Floridianson]

I had thought that the button would increase rail pressure from idle to mid rpm range. So if we add a turbo then running the stock PT we decrease the button to get higher pressure from the get go. Now if you added a PT that had a AF screw you could run the AF screw to allow more fuel from the get go and roll some coal off the line. The throttle shaft screw will also raise rail pressure all the way to defuel. So we do the button or the AF then do the throttle shaft to no more that 200 psi on a stock 250. Yes / No?

 

[simp5782]

The screw/button relationship you stated contradicts what I was reading... I was understanding it was the opposite.
Still trying to get my thoughts sorted out.

I have no coolers at this time. Due to the small injectors in the NHC-250, I am only seeing 14-15# boost, but it doesn't max until 2000-2200 & it is lower in low gears.

A #17 button is in there, but I'm seeing 210 psi, just before it defuels, at lower speeds it varies from 150-200, then spikes just before the governor kicks in.

The turbo (a HT3B) does not make a lot of boost at 1500, maybe 7#, but EGT's are not high, so it appears I could use more fuel that will spool the turbo better.

Any ideas?

What are the egt numbers? Pre or post turbo? What cfm air filter?

you arent loading the motor with just an empty truck you won't see decent boost numbers.

 

[Lonnie]

I turned in the fuel screw slightly to reduce pressure to 200. Mine is 25 psi per 1/4 turn.
I'm at 2 turns out.

My EGT's are only around 900 max pre-turbo under boost.

Yes, it is only driven empty & I can see it get more boost in higher gears due to load.
But on hills around here it is seeing full load & shows it's weakness.

Not sure about the AF screw... it has a screw where 1 would be, but it is recessed in the pump, not like the AF screws I see with a lock nut on them. I didn't mess with it.

My question would be... What is the difference if I swap from a 17 to 22 button & then bring the pressure back up with the screw?
Or do I go the other way with a #10 & tighten the screw more to stay at 200 psi? How would any of these change the mid range fueling?

 

[Floridianson]

My .02 without more up grades #17 button and 200 rail plus your 900* your looking good. Seem like it is a rabbit chase to gain just that little more. With bigger injectors to eat the higher rail pressure then more heat so then after cooler then something else to keep EGT's down. I do not believe you going to see / feel a change with chasing that fuel button any lower.

 

[Lonnie]

I'm ok with the top end power, but I would like to get more in the mid range.

At 1500-1600, I'm seeing under 150 psi pressure & about 7# boost with EGT's in the 800's.
Here is where it needs more to pull through & spool up, otherwise you try to hold that speed with it floored or downshift & then hold it at redline at a slower road speed.

 

[Floridianson]

I never put a turbo on any of mine. Just found this thread and post #9 talks about plugging a hole in the head if we add a turbo.


https://www.steelsoldiers.com/showt...s-With-Allison-Transmissions&highlight=button

 

[simp5782]

I'm ok with the top end power, but I would like to get more in the mid range.

At 1500-1600, I'm seeing under 150 psi pressure & about 7# boost with EGT's in the 800's.
Here is where it needs more to pull through & spool up, otherwise you try to hold that speed with it floored or downshift & then hold it at redline at a slower road speed.

As soon as you put the throttle down you should get increase in rail pressure. Full throttle being max RP.

Cruising at 1500/1600rpms you should not have any pressure if you put your foot in it your pressure will vary between the throttle percent. I don't know why you would not have any higher rail pressure.

I would reflow the injectors. And increase your fuel delivery line. I was running 3/4" hose on my BC.

The manual transmission on the 809s has huge gaps 3 to 4 and 4 to 5 that are tough to overcome

https://youtu.be/K-f8GHWCq0c

https://youtu.be/qXJ3-zy7vWU

 

[Lonnie]

I never put a turbo on any of mine. Just found this thread and post #9 talks about plugging a hole in the head if we add a turbo.

Thanks for info. Those holes are plugged on my engine.

 

[Lonnie]

As soon as you put the throttle down you should get increase in rail pressure. Full throttle being max RP.
Cruising at 1500/1600rpms you should not have any pressure if you put your foot in it your pressure will vary between the throttle percent. I don't know why you would not have any higher rail pressure.
I would reflow the injectors. And increase your fuel delivery line. I was running 3/4" hose on my BC.
The manual transmission on the 809s has huge gaps 3 to 4 and 4 to 5 that are tough to overcome

I also have low rail pressure at idle & cruise, the pressure only climbs high when I'm at full throttle.... but it only sees about 150 psi at 15-1600 instead of the full 200 psi.

 

[simp5782]

I also have low rail pressure at idle & cruise, the pressure only climbs high when I'm at full throttle.... but it only sees about 150 psi at 15-1600 instead of the full 200 psi.

You should have no rail pressure at idle or cruising. A rail pressure gauge is to help with mileage by showing limited or no throttle pressure to maintain the speed while cruising.

Its like a nagging wife to let you know when you are using too much fuel.

 

[Floridianson]

I also have low rail pressure at idle & cruise, the pressure only climbs high when I'm at full throttle.... but it only sees about 150 psi at 15-1600 instead of the full 200 psi.

From what I understand you will never see the 200 psi at 15-1600 rpm. What we don't know is how much performance gain when we drop one lower button size and change full rail pressure. You might have gotten the same amount of power / performance with a 20 button and 185 total rail pressure before drop off. That's with your stock injectors. Yes others have said they could tell the change in the button helped with adding a small amount of psi down lower and increase in total rail. I do believe if you had put a lower range gage on the PT before you changed the button you would have seen a change in the idle pressure. There would have to be some pressure at idle just to push the fuel around the fuel loop system back to the PT. I still believe your good all around right now if all other things are correct. Plenty of air and injectors adjusted. So my .02 be happy or follow the white rabbit to the red or blue pill. Meaning increase / rework injectors for more fuel then might have to deal with the heat so intercooler and what ever else to get where your happy.
I never expected much from the 250 in any of the trucks not like any of my 400 Cummins that I had or my 400HP series 60 in the 915 I drive now.

 

[simp5782]

Ive got an aftercooler if you are needing one. Its a good take off from a BCIII

 

[Lonnie]

Is 200 psi a realistic safe limit on the line pressure?

I spoke with Pittsburgh Power about getting the injectors flowed.... I would be fine with spending money on injectors if I could drop pressure for more reliability.

 

[simp5782]

Is 200 psi a realistic safe limit on the line pressure?

I spoke with Pittsburgh Power about getting the injectors flowed.... I would be fine with spending money on injectors if I could drop pressure for more reliability.

Premco is around $75 an injector for top stops. Which you probably do not have top stops.

I wouldnt trust pittsburgh power to touch crap to be honest.

 

[Lonnie]

Thanks... good to know. I thought they had a good reputation with these engines?