Cranking VE Cells
 

My car has been tough to get started lately, I finally realized that the issue started when I went to bigger injectors. I changed from 550 to 660 injectors and the car was running rich, but well enough that I just retuned from the map I had rather than adjusting Req Fuel. I dug up an old MSQ and sure enough, my cranking cells (far left column, 100kpa-50kpa) had never been retuned after the injector swap. I pulled out 20% fuel from those cells and the car starts much better.

This got me wondering how far away from "correct" my cranking cells actually are. I was wondering if you guys would mind posting up the numbers you're showing in idle cells vs cranking cells. Currently I've got my cranking cells set at 76 and idle is 72 (obviously the numbers are going to be different from car to car, but I'm assuming the ideal ratio would be basically the same), I'm wondering if I should pull a little more fuel when cranking and see what happens.

(Hopefully that makes sense, I tried to explain it the best I can. I'll be happy to clarify if something was unclear.)

What as ass backwards way of tuning.

You should've changed Req_fuel, and then you should've changed your cranking settings As it's those which directly effect whether your car will start or not.

What Rich said.

In my case, the only VE cells that are tuned in the lowest RPM column are in the idle region (55kPa and below), because it's darn near impossible to hit the others. So the rest of the cells in that column are extrapolations from the higher RPM cells. My lowest RPM column (800RPM) goes:

100kPa VE=59
84kPa VE=52
75kPa VE=45
55kPa VE=45
35kPa VE=44
26kPa VE=44
19kPa VE=44

if you had changed the req_fuel proportionately, there's be no issue here, the fuel map could pretty much stay the same. It's a multiplier and the correct method for injector size changes, now you need to retune the entire map instead of minute little changes.


with that being said, it's smart to tune your entire fuel map in ALL areas.

take a look at mine:
https://www.miataturbo.net/attachmen...1&d=1310125208

Thanks for the numbers, should point me in the right direction.

As far as my idiotic tuning practices. I understand that req_fuel is a multiplier. I put the injectors in, changed req_fuel down 20% and drove around. The car was running very lean at cruise. I then reloaded my old map and it was running normal AFR's at cruise (at WOT it turned out to be rich like you would have expected the full map to be). It was my personal preference to lean out a car that was running too rich than try to add fuel to a car running too lean.

Sounds like the new injectors have a longer dead time. (Leaner than you expect at short on-times)