Tuning injector PWM & PW
Posted: Tue Mar 08, 2011 11:06 am
Hi, I'm working on my first install, and don't think I'm setting the PWM current limit for the injectors correctly. Details:
- MSII PCB ver 3.0
- SBC 350 with TBI & 55lb low-impedance injectors on top of a Edelbrock Performer dual-plane manifold. RV cam.
- Fuel only (for now)
The engine starts right up & idles well with the 'stock' cranking phasewidths - no problems there. But when tuning the PWM parameters, I'm able to go clear down to 0 PWM Current Limit %, and ~0.8mS PWM Time Threshold (any lower & the engine dies). At 0% current / 1.0 TIme, the engine idles fine, and doesn't seem to stumble when I stab the throttle (although AFR goes way high - but I think I deal with that later). But the 0 PWM current seems crazy low! The idling PW at these settings is ~1.3mS (which also seems low).
I have the Injectors running 8 squirts per cycle (alternating), and the Req. Fuel is 8.3 (not exactly sure what that means). I've tried other settings (variations of fewer squirts & simultaneous / alternating), using the 'stock' PWM settings (30% Current, 1.0 Time), but the engine idles much better with 8 squirts.
(MSQ & datalog attached)
So:
1) Given that engine idles well, should I just move on to load tuning, ignoring the idea that PW & current limit seems really low?
2) Anybody have any advice on # squirts & alternating vs simultaneous for GM TBI units? Where are these parameters in the MSQ? (I have the MSQ from the DIYAutoTune '77 Nova project, but can't find the # of squirts settings).
3) (separate question) I only have 11psi fuel at the TBI inlet. Should I consider a rebuild of the pressure regulator to get closer to 15psi? (I know that this will force me to re-do all my tuning again).
Thanks!
- Kelly
- MSII PCB ver 3.0
- SBC 350 with TBI & 55lb low-impedance injectors on top of a Edelbrock Performer dual-plane manifold. RV cam.
- Fuel only (for now)
The engine starts right up & idles well with the 'stock' cranking phasewidths - no problems there. But when tuning the PWM parameters, I'm able to go clear down to 0 PWM Current Limit %, and ~0.8mS PWM Time Threshold (any lower & the engine dies). At 0% current / 1.0 TIme, the engine idles fine, and doesn't seem to stumble when I stab the throttle (although AFR goes way high - but I think I deal with that later). But the 0 PWM current seems crazy low! The idling PW at these settings is ~1.3mS (which also seems low).
I have the Injectors running 8 squirts per cycle (alternating), and the Req. Fuel is 8.3 (not exactly sure what that means). I've tried other settings (variations of fewer squirts & simultaneous / alternating), using the 'stock' PWM settings (30% Current, 1.0 Time), but the engine idles much better with 8 squirts.
(MSQ & datalog attached)
So:
1) Given that engine idles well, should I just move on to load tuning, ignoring the idea that PW & current limit seems really low?
2) Anybody have any advice on # squirts & alternating vs simultaneous for GM TBI units? Where are these parameters in the MSQ? (I have the MSQ from the DIYAutoTune '77 Nova project, but can't find the # of squirts settings).
3) (separate question) I only have 11psi fuel at the TBI inlet. Should I consider a rebuild of the pressure regulator to get closer to 15psi? (I know that this will force me to re-do all my tuning again).
Thanks!
- Kelly