smoke screw adjustment

[southpaw]

Help someone, I have an 89, and a 2002, witch will run circles around my 93. I,ll run down what i have done to the 93 so far. I bought it with about 80K on it 2yrs ago. it has always given terrible fuel milage but has improved with each fix . I replaced the thermostat, it was stuck open. valves adjusted, new tires, AFe filter and vented box, timed with dial, pump advanced max,star wheel 3/4, pin rotated 180,smoke screw untouched, this vehicle had a rebuilt injection pump installed just before i bought it . I have been reluctant to turn the smoke screw up because of the already bad consumption but now its time. My question ?could the smoke screw possibly increase milage and will added fueling possibly bring the egts down a bit if the engine is starving for fuel. I don,t believe it smokes at all or very little. fuel consumption has gone up from 13mpg to 17mpg as best I have been able to check. My next move is to turn the star wheel to max and fuel screw in maybe %50, then adjust from there. I know this vehicle has a null turbo I can,t change that part yet, it a future project . I have put in all the guages, Egts seem to get up quickly into the yellow zone running up a grade with no load. it cruses 70mph at about 18-1900 rpm. aint it fun bombs away.

 

[dpuckett]

1) More fuel will make for higher EGTs, all else being equal. You need to balance the fuelling increase with an airflow increase, which you seem to have started on. Try a 16cm exhaust housing to increase spool up and get more air in there. What kind of EGTs do you run at cruise on flat ground, 60mph? ANd where is your thermocouple- manifold or exh pipe? If it is in the pipe, it may not be entirely accurate for what is in the manifold; the subtract 300deg rule (for post turbo) is unreliable, IMO.



2a) When you set the timing, what did you set it to? And how did you find TDC? If you used the timing pin, you need to verify its accuracy. I am lucky enough to have 2 trucks that the pin is dead on (w/in 1/4 deg) TDC. Others here have had their timing pins off as far as 5 deg one way or another, rendering a timing set a waste of time when relying on the pin.



2b)What do you mean by pump advanced to the max? If you advanced it too far (like the 2. 05mm I ran for a short time), you run into a loss of bottom end, increased fuel consumption, excessive cylinder pressures, etc. I have had good luck in the 1. 5-1. 7mm @ TDC, depending on elevation.



4) What kind of shape are your injectors in? If they are crudded up, or the pop pressure is low, that can bring your MPGs through the floor. I had a 93 W350 that passed emissions with 6% opacity (almost no visible smoke), yet the injectors were popping open 500psi low. Got them reset, and gained 4MPG.



5) After all that checks out, your transmission may be a little weak, esp the torque convertor, though they normally are good to 150=200K, IF they are maintained properly. That means changing fluid/filter at the time interval if you havent reached the miles yet.



Good luck in getting yourself up to the 18-20MPG mark. Mom's 92 got 20MPG intown when I owned it; now gets 17-19.



Daniel