Staged injection 87-89 injector flow

[scott87star]

Tuning staged injection on a stock throttle body setup on my 87 Starion. MS-I chip in a V2.2 board, I noticed in the datalogs that whenever my second stage kicked in the AFR dropped about three points and stayed that way until it went back to primary only. I used the given 580 and 1080 primary and secondary injector flow rates to get the staging factor used in the software which worked out to 179 ((primary/primary + secondary)*512). Dropping from 14 to 11 AFR was not going to work, I realized that the injector flows must be different so I went ahead and measured and while I was at it I measured at some different pressures. I have a jectorate board that you can set up to pulse the injectors a preset number of times at different pulse widths and calculate flow and I built a test rig that uses compressed air over the test fluid to supply pressure. Here's what I got, all in cc/min:

 

30 psi primary 474 secondary 844

40 psi primary 537 secondary 958

50 psi primary 610 secondary 1060

60 psi primary 650 secondary 1166

70 psi primary 721 secondary 1250

 

So the primary is flowing a bit higher than rated and the secondary is a bit less. The new staging factor is 185 and yes, it solved the problem. Its interesting that 6 points out of 180 or 3% could cause such a big change in AFR.

 

Scott

[dmyers151]

Good stuff.

 

Can't say enough how much I love solid numerical data.