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
Tuning injector PWM & PW
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Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0). For tuning/troubleshooting questions, please attached a datalog and your MSQ file to your post.
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
Tuning injector PWM & PW
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Re: Tuning injector PWM & PW
Some follow-up info on this...
The engine idles well at 4 squirts simultaneous or 8 squirts alternating. 8 / simultaneous also works, but the idle is less smooth. Any less & it cycles erratically, almost dieing each cycle, until it finally conks out.
I spent some time this afternoon looking at AFRs at idle (I have a WB LC-1), and playing with the VE Analyser on the MegaLogViewer. AFRs were quite low (11-12), and VE Analyser suggested a pretty good cut to the VE table in the idling area (to the mid-teens). I implemented the changes, but found that the AFRs didn't change. VE Analyser now suggests entries in the 8-10 range in the idle cells. This seems ridiculous, so I didn't try it.
I don't have my mind completely around this, but considering all the data, I'm thinking that somehow my injectors have a lower limit as to how little fuel they are capable of spraying. These are 'field tested' injectors, so maybe they're worn out? What happens to injectors as they get old?
Anyone's insights on this would be appreciated!
Thanks,
- Kelly
The engine idles well at 4 squirts simultaneous or 8 squirts alternating. 8 / simultaneous also works, but the idle is less smooth. Any less & it cycles erratically, almost dieing each cycle, until it finally conks out.
I spent some time this afternoon looking at AFRs at idle (I have a WB LC-1), and playing with the VE Analyser on the MegaLogViewer. AFRs were quite low (11-12), and VE Analyser suggested a pretty good cut to the VE table in the idling area (to the mid-teens). I implemented the changes, but found that the AFRs didn't change. VE Analyser now suggests entries in the 8-10 range in the idle cells. This seems ridiculous, so I didn't try it.
I don't have my mind completely around this, but considering all the data, I'm thinking that somehow my injectors have a lower limit as to how little fuel they are capable of spraying. These are 'field tested' injectors, so maybe they're worn out? What happens to injectors as they get old?
Anyone's insights on this would be appreciated!
Thanks,
- Kelly