Quote:
Originally Posted by turf
hey there.
my bus used to be an all mechanical 12v, but im the llucky new owner of a allison electronic conversion.
so... i want to tune it up a bit to run best with the new trans.
inthe few short drives i;ve been on... it seems to not downshift very well and luggs easy.
on another thread i was talking about how im set to roll a bit of coal with my smoke screw.
so tonight im sitting here and wondering if the 2 are related.
if i roll back the smoke screw , which to my understanding controls fuel from 0-5psi boost, i should reduce the lugging maybe?
im not sure what kind of boost im running when lugged out, but i would think 0. so if i back off that screw, maybe my luggin issue clears up?
does that sound valid?
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if Lugging easy... I had issues with my red bus with lugging.. granted not a mechanical cummins.. But..
it was a 70 MPH maxx bus before my 6 speed allison conversion so after the 6 speed swap I was over-geared for 6th gar for sure and really at times i turned off 5th if I was up and down in the hills. not sure what your original top speed was.. I regeared and solved that issue
the TCM I got from CAC tended to want the transmission to be in 6th gear as quick as possible.. it shifted low for my liking.. since i am using J1939 electronic throttle, I didnt have any mechanical geometry that I could correct to raise the shift points of the transmission... I ended up getting a different TCM that I can tune..
in your case i think the TPS is still misadjusted or doesnt have the right curve for your engines pump profile.. im guessing the more the cable Pushes out, the higher the TPS value on yours? (im used to a pull mechanism and not a push).. you may eed to adjust the cable a bit so it shifts higher or uses a faster arc so that it reaches hgher shift point quicker... was hard for me to tell exactly how yours is built from the one pic I saw.. higher shift points will tend to reduce lugging... if you are changing your governer springs then you might want CAC to program you a TCM with the higher RPM profile on it which would raise your shiftpoints
in my case regearing to where I reached max RPM around 54-56 MPH in 4th gear allowed me to get great use out of 5th gear in that 50-64 range in low throttle conditions.. 65 and above 6th gear is he perfect gear to be in.. at 65 im taching in that 1900-1950 range.. you, being an I-6 might do fine with 100-200 RPM below that under light-moderate load and then have your 6th come-off if you crowd it.. thats the way it "should" work...
for me the only way I could get there was building my own shift tables....
CAC designs tend to favor the cummins 5.9's so you likely will have a much easier time getting it right when you get the TPS adjusted where it should be..