Another stupid d-jet question:, Related to a new 2.1 tune: defining terms- what constitutes "part-load vs full-load" and other mysteries Options

[DRPHIL914]

calling all d-jet masters !

OK so yes, ive read Anders etc and maybe missed it along the way, but
how or what constitutes a part-load condition?

I am trying to get my d-jet MPS dialed in on the 2.1 build. and it had been running really well, but just a tad lean still, so after going back and reverifying my timing and other settings, checking plugs aftera 750 mile trip, its really close and realizing i was probably a bit low on the fuel pressure i made that correction and then set out to do some local highway driving to test it out, and really felt good, but maybe a bit rich at low end, idle and what i was thinking would be part-load.

BUT i think i over corrected on the MPS and now i went from being in the 12-12.5 range at idle and also cruising at 3000-3400rpm, i now am running light at about 14 on that mid-range cruising. it is good on WOT so i dont want to mess with that(full load stop) .

i should have left well enough alone because i will probably be a bit heavy at idle and low end with this motor, due to a more performance minded cam profile etc.

point is, what is part-load? if i am reading my AFR meter , lets say at 3000rpm- 3400rpm and cruising on the flat, that would be part- load condition correct? so i dont want to make it more rich at cruise or on WOT, so how can i isolate the mid range or par-load to enrich it with out messing anything else up. i already messed this up trying to just lean it out slighty and over corrected.

if i adjust the inner screw by itself it changes both part and full load.
the outer screw in will richen part load i believe lean out full- load.
the Anders chart doesnt really address it.
- also i feel i cant really get idle right, it seems too rich but that might be the way the motor will be, not sure.

the MPS is a rebuilt one with Tangerine kit and adjustor screws, so easy to access and adjust using the Tangerine tools.

I may be at the point of just going dual webber with 44 IDF's, and forsaking the d-jet - OR a more modern programable EFI...... i just dont think i am getting the most power out of this motor that i should or would with better air intake and A/F mix.
intake is somewhat restricted on a stock d-jet and the injectors can only give you so much fuel. i did see somewhere anders wrote that the stock set up could support a build up to 2270 even with the proper changes( not sure what that means either),

anyway first question is - part load definition. then how to proceed to get this mid-range or par-load adjusted into a better mix with out making idle even more rich(or WOT either)

Thanks for the help.

Phil

[BeatNavy]

Phil, a couple of thoughts from me.

@Frank S , IIRC, suggested one way to identify "part load," or that point at which manifold vacuum is in the 4-5 psi range, is to run a "T" vacuum fitting off of your MPS to a hose with vacuum gauge in the cabin. It'll give you a better sense of what driving conditions are for your engine at "part load." In my case I found it instructive, and you can base your AFR numbers accordingly. Simply cruising down the road doesn't take much load or HP in most cases, so take AFR there with at least a little grain of salt, especially if you can monitor head temps accurately.

Do yo have an inductance meter to measure what it is you are changing, or are you going by AFR readings alone? If the latter, I think that's hard to do with much precision. I think you sort of need to ballpark it at that point and see how the car feels under different circumstances.

Take idle AFR readings on a T4 with a big grain of salt. Too many variations in exhaust and O2 setup, plus the exhaust gasses move too slowly through the system to put too much stock in them. I know it's tempting (I do it too), but you need to use other clues like smell and the nature of the idle (is it too low, too high, does it react a lot with small changes in air, etc.). Your idle mixture should be primarily controlled at the ECU. I imagine the ECU "slope" has some effect on that (or not, maybe someone can enlighten us), but get fuel pressure where it should be and then use the ECU.

Don't ditch the D-Jet. Carbs present their own set of issues. Also, I'm running Microsquirt, which I really enjoy, but it's not a panacea either. Still lots of fiddling and experimenting. The upside is that it's much easier to do the fiddling and measure the results.

Much smarter and more experienced people than me can chime in now (IMG:style_emoticons/default/smile.gif)