MSefi.com read only forum (Jan.15,2018)

I'm running an L-jetronic engine with stock injectors connected to the stock resistor pack. In the stock setup the injectors are connected directly to the battery through a resistor pack. The injecors have a resistance of 2.5 ohms and the resistor in front of it 1 ohm. This combination would in theory make them low impedance injectors so I went with the suggested settings in the megamanual:

# PWM Time Threshold to 1.0 msec, and
# PWM Current Limit to:
* 30% on a V3 or V3.57 main board (if you have the active flyback circuit installed).

The engine has been running fine for about 500 miles on Megasquirt now, but I'm going to drive it 10k miles to Africa in the months to come, so I'd just like to make sure I'm not missing something here.

MM78,

The PWM numbers in the manual are a starting point. You have to tune them, and that's is what you will need to do for your injectors. Only you can get the right numbers for your setup. See: http://www.megamanual.com/ms2/tune.htm#pwm

Lance.

Hmmm, I've got it completely dialed in with the current settings. Besides, I'm leaving for Africa on Saturday... What are the risks when I just leave the settings this way? I don't really look forward to having to tune from scratch again.

MM78,

You don't have it completely dialled in until you have tuned the PWM parameters, and this should have been one of the first things you did.

The PWM parameters shouldn't affect the tune in a significant way - if it does, you have other settings problems. So a re-tune shouldn't be required.

No-one can say how big the risks are for you of not tuning the PWM. Nothing may happen. You may have intermittent trouble with the injectors sticking at high throttle openings if the PWM% parameters are too high (or you could permanently fry injectors if the PWM settings are way too high). If the settings are too low, you might have trouble starting on very cold mornings or if the battery becomes marginal (depending on your code version). All of this depends on how far the settings are from optimal. But because we don't know what is optimal for your injectors, we really can't say much.

If this was mine, I would save your MSQ, and then adjust the PWM as described in the manual. It only takes a few minutes. Then you will know what change is required. This shouldn't affect the tune (the VE table, etc) very much at all. Then once you have optimized the PWM, drive it and see if all is well. If it is, then you are good to go on your trip. If the driveability changes, you can then decide how much of a risk you are taking because you know the difference between the old settings and the optimized ones. If you feel that the difference is minimal, you can revert to your old settings in the MSQ you saved, and you have lost nothing.

Lance.

Thanks Lance! I'll do exactly what you suggested.