Injector upgrades

[jmd4993]

I have a 92 w250 5spd. I'm getting a flatbed and putting a cab over camper on it and moving to Montana for school. It used to be auto. When it was bone stock in California I'd get 18-22 mpg all day even got 24 one time. But ever since I've touched the fuel screw it's at 16 or lower. I've put on the stock pin and turn the pump way down. I installed an extra long fuel screw and lost track of the turns. I've adjusted the star wheel and smoke screw as we'll. I'm looking to get the mpgs back up to where they used to be. So I'm getting injectors for more efficiency and power capability. I've heard 190s are good and 5x11s too. I was thinking of a 50-75 up gain. I have a getrag with a dual disc so I'm not racing or anything. Just want good towing and hauling ability and good fuel economy. Any suggestions is greatly appreciated thanks.

I have a fass 150, timing, 4"tbe, no air box, I believe 3.54 gears, and 30" Bfg mud terrains but have skinny ten ply towing tires too.

[RCCUMMINS89]

5x11 will be a little cleaner at idle over the 190s. The 190s will be more responsive, but have the potential to be a little hazier at idle, especially when cold. Both will net the same fuel economy.

Fuel screw setting will have no bearing on economy at a given speed, it can only affect acceleration economy. So, if your highway economy dropped...something else is to blame.

5x11 I would consider about a 40hp injector. Would that be enough, or are you looking for more? Stock turbo?

[jmd4993]

I have stock turbo but was told to get either a he351cw or an s300. I just want to have good power/towing/hauling ability with good mpgs. Have you heard if project rust bucket? They take an 89 250 I believe 2wd and get 972rwhp with 27mpg at 75 mph with a Ve pump. They used nitrous which I know is where the power came from and I know it cools down the air going in but would that cause that much mpgs. What's your opinion on water meth is it worth it? I'd be happy with my original 18-22mpgs I had when it was a stock auto.

[RCCUMMINS89]

A mild injector would be a 5x11 SAC.... for a little more money and power.... 5x12 or 5x13.

[jmd4993]

You said the fuel screw doesn't have anything to do with mpgs but when I first touched the fuel screw it went from 18 on a bad day and 20-21 avg mixed driving. To 16 17 at best. I got a fuel pin, fass150, bumped timing, no air box, 4" tbe. Now I have a 5spd which should help mpgs. It's very puzzling

[RCCUMMINS89]

All I'm saying is, is something else caused.... whether it be driving style or coincidence.

Once one has an understanding on how the fuel screw works inside of the pump, they'll realize that it is impossible for it to have a change in fuel economy at a given rate of speed. I say given rate of speed, because most folk accelerate faster without realizing it.

[ellis93]

Your fuel mpgs are probably gonna come back with afc adjustments. If you you think about it in gas terms like rich and lean (least it's how I'm able to understand it),fuel pin depth vs pedal position= more or less fuel.

I've had lots of arguments over it with people,it's how I learn

[RCCUMMINS89]

Again though... afc adjustments will only affect acceleration mpg. It has no bearing on a given speed's (load) rich/lean mixture.

[DodgeFreak]

Again though... afc adjustments will only affect acceleration mpg. It has no bearing on a given speed's (load) rich/lean mixture.

AFC it controlled by boost, if you were to loosen the spring tension wouldn't that cause it to fuel sooner\more?? Ex: just flat driving my boost is at 5ish psi I'm not sure what boost the pin starts moving but if I climb a hill and hit 10-15 psi isn't it going to fuel more since I have a "weaker" spring than if I had stiffened the afc adjustment to where the pin didn't travel as much in those 5-10 psi???

[RCCUMMINS89]

Only if you are giving it more fuel. I've had this argument many times......if your engine receives more fuel, it has no choice but to accelerate.

The difference between diesels and what most thinking is that ... we control fuel, gassers control air. If you are burning more fuel, it has to accelerate.

[RCCUMMINS89]

If you delete your afc........and going down the road at a steady speed, you are using NO MORE fuel than if you have a working afc....it ONLY affects acceleration or turbo spooling fueling.

The fuel screw and fulcrum lever control nothing more than throttle position.

[DodgeFreak]

I'm not talking about a flat road.....I understand if you are going on a flat road with the same throttle input the fueling stays the same....but if you start up a hill and have to tip into the throttle are you telling me that the afc adjustments have no bearing on fuel mileage?? He lost mpg with mixed driving. a weak or no afc will affect over all mpg....I'm not sure about you but I have no way of calculating my milage just driving down the road....I have to figure in when I'm acclerating also.

[RCCUMMINS89]

...it ONLY affects acceleration or turbo spooling fueling.

Yes, that is what I had already stated.

[BC847]

It's my experience that, all the above is accurate, in given driving conditions whether it's acceleration, or maintaining speed. But it gets back to the accelerator-pedal.
If one honestly considers their driving style, saying I want good MPGs while adding another potential 50HP in the same sentence, is often a contradiction.

Me, I enjoy the "Pull" of acceleration. I enjoy being able to safely, accelerate around a slow vehicle on a 2-lane. Knowing that, in a stock/OEM 1st gen Cummins, I'd most likely have the pedal to the floor a lot of the time. Adding bigger injectors just feeds the flame.


One can hack the IP and get good mileage, with proper working of the throttle. Or one can properly tune the AFC system, as well as the injection event timing and get more consistent improved mileage, that's a lot more driver friendly.


If you want larger injectors, then there's a good chance you'll have them do their job. That extra power costs MPGs.

All you can do is make sure you maintain or improve the engine's efficiency.

[RCCUMMINS89]

Well said, thank you.