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Old 03-17-2017, 07:51 PM   #1
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fuel plate

I did it!!

finally, after a number of years wondering how much better life would be if i just moved that little fuel plate forward, i did it.

i took out the 4 screws that hold down the AFC. one of them is a tamper proof screw, but an easyout worked like a champ getting it out.



after the cover came off, it exposes the fuel plate.



the plate was dead in the middle of the adjustment. i loosened the 2 screws holding it and pushed it forward as far as it would go. it doesn't move much. maybe an 1/8 of an inch.

here it is with the screws tightened back down with the plate forward.



after closing it back up i took it out for a test drive. maybe its better. hard to say. acceleration is alright. still slowed down on grades, so hard to say its much different. it isn't worse than when i started.

if this is all the difference it makes, i should have done it a long time ago.
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Old 03-17-2017, 08:45 PM   #2
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Be very conservative on moving the fuel plate. There are a couple of threads on 4BT swaps by folks who created a runaway conditions on their 5.9's by moving it too far.
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Old 03-17-2017, 11:31 PM   #3
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hot diggity dam Tango!

thanks for the words of wise. since your post, i've been in deep learn mode about the AFC and tuning it and the P pump.

that AFC is coming back off tomorrow for more testing.

my bus has an accelerator like a brick. on my way back from the last test run it takes some much force that i broke the cable off the pedal mount. (not the first time its done that)

after moving the plate today and test driving, it still started accelerating like a brick and i didn't notice much change. however, there was a sweet spot on the pedal, once i passed it, i thought the truck was running away, but no, the effort on the pedal just decreased and it got real easy to accelerate.

now after my reading, i think the pushing that plate forward helped my post boost acceleration. now, i think i need to back off the diaphragm pressure of the smoke screw and increase the pre boost fueling with the star wheel.

now it makes sense to me

That AFC is coming off tomorrow for some more changes.

this "read me first" thread on a cummins forum is chocked full of great links and info for tuning your diesel.

Beginners Thread - Read First! - Dodge Cummins Diesel Forum
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Old 03-17-2017, 11:37 PM   #4
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sounds similar to the navistar... in navistar they call it the anti smoke screw.. but in the end I believe the star screw is the pre-turbo spooling fueling... I would think you might want to boost that a little but not a lot..just enough to maybe help the turbo spool faster.. as you dont want to over-fuel when theres no air to get a good burn.. - alas black smoke and im guessing less complete combustion. so longer turbo spool time? though your bus could roll coal with that turned up!.

-Christopher
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Old 03-18-2017, 12:04 AM   #5
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i had never thought about tuning before until i felt the different pedal today.

from one of those links it said that a stock turbo probably doesnt spool up until 1800 rpm. for lack of knowledge in adjusting the pre turbo boost, they just stay that way.

that AFC is coming off tomorrow for some changes.

rolling coal isn't my goal. the bus has never been a smoker. i think that means its time to run the fuel a bit richer than its been and make some power.
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Old 03-18-2017, 02:06 AM   #6
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here's my plan for tomorrow i'm doing some reading here and just cut and paste steps for me to remember tomorrow.

afc mods (lots of pics) - DieselRam.com

allows greater rack travel -
replace fat washers with fender washers
remove shaft
shorten foot

This controls the 0 boost fueling, the further in the screw the more tension it puts on the afc spring, allowing more fuel to come on with no boost.

remove smoke screw cover
back the smoke screw out

adjust starwheel spring with air pressure. 20psi - half extension, 40 psi, full travel

reinstall AFC pushed in the forward position.

tighten up the smoke screw, the tighter it gets, the more fuel you get a 0 boost.
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Old 03-18-2017, 06:09 AM   #7
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I'm not sure what the stock timing is on that, often when up up the fuel you may be able to bump the timing a bit too.. I can't remember what trans you have, careful on power adding if it's a 545.. too much low end on it wiltg low rpm results in slippage and heat.

Looking forward to this to see what you come up with
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Old 03-18-2017, 05:45 PM   #8
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well worth the investment of $5 in parts.



i got the AFC back off today and took it apart. getting through those tamper screws is slow. the internet says you can pound the right size torx into it and reuse the screws but i wasn't so lucky. an old fashion impact driver and a hacksaw did the trick for me.




i took the foot out and ground down the end marked with black. the marker was about 1/8", i ground off maybe a third of that.




i installed the new washers and bolts and reassembled the AFC.



put it all back together and took it out for a test run.


so far, so good. still no smoke, so i think i need to turn the starwheel a bit more to let more fuel in. at first the throttle wouldn't move all the way to full fuel. i loosened the star wheel (which is suppose to increase fuel with boost) until the air compressor could move the foot all the way over to full fuel, but its still pretty tight. and no smoke. if the spring was slack, it should roll coal.

the smoke screw is almost all the way in. there is still some room for adjustment, but not much.

test driving the bus was a marked improvement on the feel of the pedal. it does not feel like a brick when you push the accelerator. its lighter, but i would like it lighter still.

the bus almost held its speed going up and down some mild hills, better than before. the bus felt capable of the speed, instead of barely getting there. in fact there was a bit of throttle cable left at WOT. no need to be stomping on the pedal.

egt temps range from 700 to 1300. uphill wot was 1300* coasting downhill was 700*. egt response is amazingly fast to letting your foot off the pedal too. that 1300 comes down instantly with less pedal.

more experimenting tomorrow. i need to loosen that star wheel a bit to see some smoke.
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Old 03-18-2017, 06:38 PM   #9
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Change the governor springs to get rid of the slow brick feeling. The pedal is much lighter with a 3000 rpm spring.
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Old 03-18-2017, 09:17 PM   #10
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i got one more test in before i lost daylight today.

with the smoke screw almost all the way in, i get a healthy black cloud behind me for about 2 seconds and then it clears up as i stomp on the throttle.

the star wheel is as loose as it will go. a smaller spring would be the next step.

i'll back off the smoke screw a hair tomorrow and probably call it good.

the truck is not timid anymore. you push the pedal and she goes. you feel like you could merge into traffic without any issue. its a much better feel on the pedal and transmission. less slack and slop if that makes sense.

i'm pretty happy. now if it only lasts!
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Old 03-18-2017, 09:44 PM   #11
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Nice job.

It should be about identical on mine. I've watched a bunch of youtube fuel adjustments but listening to you do it helped a lot.
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Old 03-19-2017, 04:13 PM   #12
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i think i'm done adjusting the AFC. for anyone that does this in the future, here is how i set mine.

i have the Bosch P7100 fuel pump.

stock fuel plate all forward.
AFC housing all forward.
ground ~.05" off the AFC foot
star wheel all the way out (slack spring)
smoke screw backed out. (no pretension)

the first three things increase fuel at WOT
the star wheel increases fuel during boost
the smoke screw increases fueling at 0 boost (not a problem)

it smokes when i hit the throttle under load, but only for a couple of seconds. no smoke when parked and no load on the motor regardless of rpm.
the power increase was a seat of the pants noticeable. but now i can't imagine driving it with less hp. its not a crazy amount of power, but the bus feels capable of merging in traffic, accelerating up a hill. confident. the pedal is a bit lighter than when i started.

the AFC was easy to work on, no mystery springs or bits. i only had to remove 1 end of 1 fuel line to get access to the AFC. once you have removed it, its a very easy process to repeat. getting through and replacing the tamper proof screws was the most difficult. i put in hex head cap screws and now taking on and off AFC just takes a few minutes.

moving the star wheel gave the single biggest gain. the turbo would not spool up until i was pushing 1800 rpms. now it spools up 2 seconds after you hit the pedal, and accelerates you nicely.

if you are on the fence about modding, this cheap diy one is worth it for me.
3 hours labor and $5 in parts gets you no stomach ulcer going uphill. time will tell!
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Old 03-19-2017, 08:33 PM   #13
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A most excellent write up! Thank you. May have to play with my 3.9.
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Old 03-20-2017, 10:49 AM   #14
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Thanks Tango!

i did a lot of reading on this, i think my first post about turning up the the screw was 5ish years ago. and now its done.

i absolutely heeded your warnings about runaways. most all of my diesel knowledge has come from participation in this forum. In the time i've owned a diesel, mechanics are the ones that have told me no, about turning them up. it seems that any bus owner that has, has been happy with the result.

sometimes a cummins 5.9 isnt a dodge cummins 5.9. 2 examples i've found are the fuel pump and the afc. (plus the obvious air compressor)

i have a '93 blubird, 5.9 cummins. it has the 2nd gen P7100 fuel pump. dodge didn't change to the P7100 until '94. so my first attempt learning about my fuel pump resulted in a lot of reading on what i thought i had, the 1st gen dodge vp44 pump.
another difference in the AFC is the spring. the dodge engines offer 2 lighter springs. the lighter vehicles can take more fuel with out bogging down. when i saw the difference of my spring compared to the lighter dodge springs,i was confirmed in my thinking that the motor will handle more fuel, because it does in the pickup application.

many say you can pull the fuel plate out completely and leave it out. the fuel plate is actually a WOT stop. i think it' be more inclined to runaway if you do something along those lines. custom adjustable fuel plates can get you much bigger horsepower gains than i got with this mod.

not that i found a set up chart, but it seems that people on the cummins forum know that if you have a 180hp fuel pump, xxxx fuel plate, and xx AFC spring you can adjust the start wheel all the way back. my numbers matched what i read, giving me confidence in the mod.

i think my engine was setup as "industrial" as it could be for a truck engine. so deciding to fuel it a bit more, within the parts limits just makes sense.

the improved performance changes you from a proud bus owner, to a proud cummins owner.

i've probably driven 60 miles testing the changes. the engine doesnt seem strained and just happily chugs along.

i think i read that the most likely point of failure now would be the head gasket. my bus has 320k mile so......a new head would make the motor good for another 320k?
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Old 03-20-2017, 11:00 AM   #15
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the bottom end Rarely nukes on a cummins.. most of any mechanical issues seem related t othe valve train.. of course as engines wear, the rings do end up a bit looser and you get more blow-by.. the more fuel you give it, the nore blow-by you will have..

how much is too much? i dont know that answer.. I know theres tests..

im of the mind though unless oyu feel like theres a ton of headgasket failkures around this age of the engine, or you think a valve is leaking that i wouldnt touch it...

if I had any reason to believe I was getting ready for a head gaskey failure, id pull the head, replace the gasket and while at it, measure the cylinder ridge to get an idea of how well the cylinder walls are wearing..

at the same time, send the head off and have it surfaced, and the valves done...

then you have a pretty fresh top end and you know where you are at ring-wise.. bottom ends usually speak for themselves... excessive bearing clearances and you have oil-pressure issues.. ready to nuke and it usually makes a lot of noise..

-Christopher
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Old 03-20-2017, 11:15 AM   #16
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Seems that just about all of the Cummins HP builds on other forums started with new and stronger studs for the heads. Seems the stock ones stretch a bit when the ponies get pushed and that's where the gasket failures come from. Other folks swapped the studs just for the added gasket security.

The only lower end mods I have ever seen were on insane 1200+ hp sled pullers and such. As Chris noted, they seem to be pretty much bullet proof otherwise.
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Old 03-20-2017, 11:31 AM   #17
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head studs are the way to go on any high HP diesel.. even stock... after all the ford guys learned this real quick with the 6.0's.. one of the first real bullet-proofing techniques in the 6.0 was to swap bolts for studs..

-Christopher
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Old 03-20-2017, 11:35 AM   #18
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Pretty cheap insurance actually.
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Old 04-08-2017, 08:27 PM   #19
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just finished installing a bunch of new filters today and thought i'd give her a test run. 0-60 in about 40 seconds!


https://youtu.be/eJgRhf84Zkw
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Old 04-11-2017, 02:25 PM   #20
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here is another short video of the smoke i get from the pipe. that's not exactly rolling any coal! watch the mirror. its hard to drive and film at the same time..

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