cummins 855 fuel button?

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So I'm seeing stuff on changing out the fuel button to increase fuel pressure. I have yet to crack mine open to see what button I have.
If I understand this correctly, I need to put a butt in that is numerically a few numbers smaller.
Is this acceptable practice?
Will it cause damage engine damage?
Is there a noticeable increase in power?
has anybody had any experiences with this good or bad?
 

74M35A2

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Correct. A smaller # fuel button on the 250 engine delivers more fuel, which increases power output, which increases EGT, which increases the risk of liquefying your pistons. Install and use an EGT gauge, and gains can be realized safely. Recommend the dual fuel line mod also if you have not already. Look it up.
 

wreckerman893

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Driving a "HOT" diesel requires a special skill set to keep from destroying the engine.

As stated above you need a pyrometer and you have to know when to back off the throttle.

I once melted a piston because I was driving someone else's truck.

These were company trucks and this bird didn't bother to tell me he had had the fuel turned way up.

I got into a hard pull on a long hill and kept my foot in it until Number Three piston decided it couldn't stand the heat anymore.

You also have to turn the air to a diesel to help burn all that extra fuel.
 

Floridianson

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As said above pyro and you should have a 200lb fuel pressure gage. I myself would not go over 200lbs as stock is about 175lbs. You can hook it to the upper port for the test and buy dropping the button and adjusting the center throttel shaft screw you will get a increase of performance.
 

wcuhillbilly

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I messed with this on my 250, over on the thread "816 jakes and turbo" I have been stumped for some time now as the dual fuel line and button change did nothing. THus i likely have low rail pressure.
Notes.... I had a #32 in mine, I then turbo'd it and had some noticable power and less black smoke. I then put a #17 button in from a donor pump. this really didnt do much, but bump up the idle some, as the button is actual called an idle spring plunger... If you ask Cummins for a fuel button they will look at you like you have two heads.... I installed a pyro and the numbers where ok, so I installed a dual fuel mod and my top RPM dropped 450rpm.. thus top rpm was around 1650. where it had been 2200..... I pulled the rear leg of the dual fuel and cap'd it, and now the RPMs are somewhat back to normal...
Idle spring plunger part #
#10=141625
#12=141626
#15=139894
#17=140417
There is a more extensive list around here somewhere, search for "fuel button" or Idle spring Plunger" but you will likely end up somewhere around 15-22 and these are old part number so get ready for a superceded list of new numbers.


Like others have said be extremely careful modding the old 855 it's no C-15 Cat and will never come close. Respect it for what it is and be nice to it and it will serve you for years. If a hot rod is what you want, go find a modern Cummins, cat or Detroit and twist it till your wallet says otherwise
 
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73m819

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I dropped my button in the 36,000 lb m819 from a 27 to a 22, what a difference, more pulling power, where I had to downshift from 5th to 4th, I now stay in fifth, Be REAL careful fueling up, NO MATTER what everybody says" I dropped to x and everything is great", the 250/265 (265 was not a long used engine) does NOT have piston squatters (coolers), fueling up gets the pistons HOT very FAST, the higher the fuel up the faster the heat buildup, the piston can handle the HEAT to a point, even several times, BUT at some point there will be no turning back, EVEN with a pyro, pulling a long grade the heat can build so FAST the damage is done before you can get out of it,

There is another thing to consider is MAX rpm, fueling up at times increases the max rpm (I gained 50 to 2150) again NO MATTER what other people say" I bumped my rpm X and everything is great", the Cummins engine is designed to run at 2100 or a bit over, at 2400 the valves start to float and maybe start hitting a piston, 2500 they ARE hitting the pistion, 2600, you just brought a head, some rods, valves. Now if you have the rpm up to 2350 (max test rpm for the ip, NOT the engine), you go down a long hill which will tend to bump up the rpm, a lot more then 50 rpm, you are now in the float specs., things WILL NOT get better unless you slow things down (BRAKES then downshifting, though downshifting may not help the issue).
 
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wcuhillbilly

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Sorry for calling it a fuel button. I got this terminology from this video that is a great brake down of the whole injection pump.
https://m.youtube.com/watch?v=KzuwdxEJfQA
No worrys, most refer to it as a button, looks like a button,,,,, engineers commonly call a simple item a complex term... IE: who ever heard of a propeller shaft on land,,???? thats the technical term for a driveshaft..... :cookoo: good video...
another way to turn up the fuel is to drill out the ball bearing plug in the end of the throttle shaft and turn the screw... Counter clock if i recal correctly opens up the fuel. Mine just had a plug of gum in the end of the shaft thus it was easy to get too.... and too much messing with it will result in what wreckerman and 73M819 refered too.... mucho melto downo.
I have a worn out fuel IP and no time/money to work on it, so I put up with low rail pressure and limp it along untill I can get into the pump and fix it correctly.. The turbo and the fuel line mods net most guys a good drivability gain. I for one am looking into using the power I have in a better way to stay in an RPM range. IE converting to a 10 or 18 spd trans, thus instead of a 1200 RPM drop with a shift. Im dropping 250 rpm thus keeping my power to the wheels
Good luck, and find some jakes,,, they will save your juice brakes and set off car alarms..... When your ready for some real power, look around and find a B model Cat to stuff in there.
 

simp5782

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Stock they come with a #27 button. You can drop 4 buttons and be safe. You can also run a dual line kit and get more power. If you up your button you have to drill the ball bearing out on your throttle shaft to adjust it COUNTER CLOCKWISE about a 1/4 turn. Or just take your pump off and have it done professionally on a bench test so you know you are set right. I have a #20 in mine and only a single line kit. It has tons of power and not much smoke. I am impressed with it so far. Throttle response is 100percent better than before. Also remember on a 250 you have more power about 10% before WOT You can feel the power band and the drop off on the throttle when you open it up.

You want more power get the pump redone so it is set right. Get the dual fuel line kit. You can actually go to a hydraulic shop and get all the fittings and hoses for about $100 or so.

https://youtu.be/mvQsUXV8bPE
 

Trent Britton

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Elkcity Oklahoma
I messed with this on my 250, over on the thread "816 jakes and turbo" I have been stumped for some time now as the dual fuel line and button change did nothing. THus i likely have low rail pressure.
Notes.... I had a #32 in mine, I then turbo'd it and had some noticable power and less black smoke. I then put a #17 button in from a donor pump. this really didnt do much, but bump up the idle some, as the button is actual called an idle spring plunger... If you ask Cummins for a fuel button they will look at you like you have two heads.... I installed a pyro and the numbers where ok, so I installed a dual fuel mod and my top RPM dropped 450rpm.. thus top rpm was around 1650. where it had been 2200..... I pulled the rear leg of the dual fuel and cap'd it, and now the RPMs are somewhat back to normal...
Idle spring plunger part #
#10=141625
#12=141626
#15=139894
#17=140417
There is a more extensive list around here somewhere, search for "fuel button" or Idle spring Plunger" but you will likely end up somewhere around 15-22 and these are old part number so get ready for a superceded list of new numbers.


Like others have said be extremely careful modding the old 855 it's no C-15 Cat and will never come close. Respect it for what it is and be nice to it and it will serve you for years. If a hot rod is what you want, go find a modern Cummins, cat or Detroit and twist it till your wallet says otherwise
Is a # 10 going to be to much fuel? That’s all I could find.
 
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