Detuning the 5.9

[AndrewKing]

HI All,



I recently bought a 1989 d250 with auto trans. The truck seems to run fine and gets 20. 3 MPG at 63-65 MPH... . Problem is it tends to smoke a little at idle... Not blue smoke but black smoke... . So I am assuming it is overfueling?... . I don't currently have a boost or pyro on the truck... . Also, I would like to Detune the truck for less power (I know... I Know I really don't want to BUT my helpers will be driving the truck for lawn care and I don't want to even risk them messing up the transmission by being to hard with too much power)... . Is detuning as simple as doing the reverse of turning up the power..... I don't want to retard the timing or do anything to make the truck less efficient (because I am paying for the fuel)... I just want to make the truck not smoke at idle, get good MPG's by being efficiently tuned and be less powerful so as not to stress the trans... .

Thanksfor any and all help.

Andrew

 

[DVolk]

My guess it has a littel larger injectors than stock or it needs some injector cleaner ran through it .



On the de tuning i wouldnt do it , but id do one of 2 things , one is cheap the other will cost you a littel but well worth it .



option 1 drill a hole in the floor board and install a large bolt and washer

sticking up a littel so you only get 3/4 throttel .



option 2 go to a truck wrecking yard or else were and get your self a

truck tattel tale , it records the time miles per hour engine rpms ,

and the lenght of time the truck was driven ,or sitting .



With this option youknow how yourtruck is driven , some have a warning bell to alert the driver to back off or be fired .

 

[sdstriper]

You should do several things that will require a little tune and testing. Like check the star wheel setting, smoke screw and where the pin is set. Has the fuel screw lock collar been removed, I would guess yes. And I would put a hidden valet switch on it.



Folks are going to want an accurate profile on the truck. Where are you located?

 

[dpuckett]

If it's smoking at idle, I'd check the air filter and injectors. Air filter is obvious; injectors can get plugged up or wear and pop at a lower pressure, causing all kinds of havoc. The 20. 3mpg at 65mph isnt bad, though. Bout like a 4. 10 with OD should do.



Unless you have some yeah-hoo employees that will constantly be brake torquing and burning the tires, I wouldnt worry about detuning it. It may be at factory settings as it is. I can understand not wanting company drivers to break things, but if you have to worry about that, it may be time for some new hands.



Tighten up the starwheel, loosen the throttle linkage a little, back the smoke screw out- basically all the opposites of what we "normally" do to these trucks. One reason to NOT mess with the fuel screw is that it can actually HURT your MPGs. I know it sounds unreal and illogical, but is true; BTDT. The 727s seem to be better than the later 518s about transferring power, so it may SEEM like it is stronger than it is.



And, once you get it to 6. 2 Chevy gutless, dont tell any of your hands about the TDR.



Daniel



Daniel

 

[sdstriper]

You could run the high idle screw out to limit throttle travel too.

 

[AndrewKing]

Thanks for the help so far... . I did look at the air filter and it was a little dirty... . Actually probably pretty dirty... . it was so dark that when held up the filter to the sunlight it blocked alot of light... . almost like a welding helmet... . New filter was like night and day... . I am hoping to see if this helps to clear some of the smoking at idle at least..... I am a little afraid of trying new things (like messing with the pump but I think I will risk fiddling with it a little)..... I like the hints about how to limit full throttle... . That I will definitely do... . I would also like to make some adjustments to make the power come on more gradually and possibly even less powerfully... Well maybe limiting the pedal travel to 50% or so will help also. In one of the earlier posts it was mentioned that messing with the fuel screw can actually hurt mileage... . You are right it does seem illogical that lessening the fuel would hurt MPGs?... Well, I'll try some of the other settings at least. Maybe even a heavy dose of fuel treatment to boot... . While I'm thinking of it could a dirty fuel filter cause smoke problems too?

Thanks again

Andrew

 

[AndrewKing]

Oh I almost forgot... . What is a valet switch?... . IN answer to another question, I am located in Charlottesville, VA...

Andrew

 

[phillips5]

If it smokes at idle sombody installed pod injecters or the like or the injecters need attention. You can back out the AFC screw a ways to delay the power. This will save on tires. That early 727 will burn the tires if there not carefull.

 

[sdstriper]

I wouldn't be afraid to make any adjustments to the pump. Take a note how many turns you make on the fuel screw, star wheel, smoke screw etc. Check the milage a tank or two and you can always turn them back.



You can loosen up that throttle linkage pretty easy as well as tighten the high idle throttle stop. I would adjust the transmission kickdown cable if I messed with the throttle linkage adjustment much.



A valet switch is a solenoid valve that can block off the boost to the AFC. With no boost to the AFC, you could rod on the truck and still not have EGT trouble etc. Flip the valet switch to allow boost into the AFC and you have your AFC boost back. There are several How-To's on this on the net, here or DTR IIRC.

 

[JLEONARD]

If I drove a truck that had a valet switch I would energize it... at least just to see what the switch did.

Then I would switch it on while driving and switch it back off at the end of the day.

Just food for thought.

The best bet is to turn the fuel pin to "dog" position. Then your drivers can't experiment with the mystery switch.

 

[sdstriper]

And I would put a hidden valet switch on it.

Hidden switch Jay! I been an employee type once err more than once...

 

[PToombs]

Buy a cheap chibby for the workers and keep the good truck for yourself! :-laf Then you don't have to detune nuttin!

 

[sdstriper]

These CTD get four times the mileage Pete. NS, That is why I got mine. I'll never buy another gas engine truck again. I was already a Dodge man, just never had a diesel. Wow, what a learning experience this has been.

 

[Moab4x4]

I used a keyed switch for the valet switch for my teenagers, but I agree, simpler (and less tempting) to just turn the fuel pin to the least aggressive position and tighten up the afc spring starwheel.



When I backed off my fuel screw 1/2 turn, the initial blast of smoke pretty much went away. ... ... ... ... ... Then I turned it back. :-laf

 

[AndrewKing]

HI all,

Thanks for the replies... . I am a little nervous at making the adjustments... Can anybody post pics so I can see exactly where everything is that I need to adjust?... . I played with the linkages and I did figure out which screw was the low idle stop and which was the high idle stop... Only problem with the high idle screw was that there was some sort of cover over the screw head... Is it a problem If I accidentally break this off so I can make the adjustment to lessen the throttle travel?

Thanks again for the help.

Andrew

 

[AndrewKing]

Oh... By the way... The new air filter did not make the smoke at idle go away... . Maybe the fuel pin needs moving... Where is this thing hiding?

Thanks

Andrew

 

[MEby]

Oh... By the way... The new air filter did not make the smoke at idle go away... . Maybe the fuel pin needs moving... Where is this thing hiding?

Thanks

Andrew

The fuel pin is located on the top of the pump underneath the afc cover. The cover is held down by 4 small bolts. there is also a boost line attached to the rear of the cover by a banjo bolt. Be careful how you tighten it back down though as the cover is very thin walled. Check out the stickies in the faq forum, I think I have seen photos in there.

 

[dpuckett]

If the filter didnt fix the smoke, you have timing or injector issues to contend with. I'd run it for a while and see if you get used to it or it clears up.



It wont hurt anything to "accidentally" remove the high idle stop cover. It is for warranty, anyway, which expired long ago.



If you break the pot metal tube going from the intake to the AFC housing, I posted a fix for it eons ago in the Discontinued Parts sub-forum, even got published in the magazine about 2yrs ago.



DP