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

I just got my tfi setup running, and have an issue that seems to conflict with a part of the ms2 tfi setup instructions. At low rpms (less than 1000, my tach was acting eratically, and the car acted like it had weak spark. The only way to "fix" it seemed to be to increase the dwell to 2.5-3 ms. The setup documents said to set dwell to 1ms with no battery compensation. Did this mean set the maximum spark duration to 1ms, and dwell might need to change? This seems to work. I felt my coil and tfi module and they don't seem to be that warm. Can I mess anything up like this? I am about to take it down the road and tune, any suggestions will be welcome. It is the normal "grey" module.

Wes,

The TFI set-up isn't 100% tested. 3.0 milliseconds shouldn't hurt anything, and if it helps, then use it! Let us know what works, and we'll change the instructions to match that.

Lance.

Thumbs up! Another turboford liberated from the LA3!

3 ms seems to work well, I think I may need to also increase maximum spark duration slightly. I am not really clear on what dwell and maximum spark duaration means in relation to the "control" signal.

Has anyone got this going on TFI with no issues yet? Above 1100 or so rpm mine is perfect. If it drops below 900, it will die down to the cranking rpm and just barely chug along. Increasing the dwell to 3ms seems to help, but it still does it. Does anyone know what could be happening? I noticed with msns-e, it has a fixed duty dwell option, and that is what the tfi people seem to run. Unplugging the spout makes all of this go away. It otherwise is running fine. While the dwell was up this high, it also "stumbled" about 4 times above 3000rpm. With the dwell down it never did it (could just be coincidence). If I can't figure this out soon I am just going to buy an msd box. ALso, it will crank fine, and then start to stumble. If I can get it above 1100 or so after it does it it will run fine. I also found in a search some info about trying to get a duty cycle style output, and it was suggested to enter the same value for dwell and spark duration, but just really big (like 100ms). I would be will to try this, but is it safe?

it was suggested to enter the same value for dwell and spark duration, but just really big (like 100ms).

wes kiser,

Yes you can do that, what it does is essentially give you a 50% duty cycle on the output signal. MegaTune probably won't like numbers bigger than 25.5 for the max spark duration, or 8.0 for the dwell though, so you'd have to edit the INI file (megasquirt-II.ini) to allow bigger numbers (this is documented in the INI files themselves).

You could try 8.0 and 8.0 to start with to see if it helps at all....

Lance.

8 and 8 seemed to help. I am going to read up on how to modify the .ini file and try big numbers.

Modified the .ini to allow 25 on the dwell. 25 and 25 seems to do well, but the tach is "shakey" at idle. Is there a chance 50% duty cycle is a bit much? Would putting 16 in for dwell and 25 in for max spark duration yeild approx a 30% duty cycle? If that is the way it works I may play with the values and see if there is an "ideal" setting.

Wes,

Yes, that's how it works, 16 dwell and 25 max. spark duration would be:

16/(16+25) = 16/41 = 39%

To get 30%, you could use dwell = 11, max. spark = 25 for:

11/(11+25) = 11/36 = 30.6%

Lance.

Thanks, I tried it, and it seemed to run a little better with the 50% duty cycle than any other way. I think the only other issues I have left are just good old tuning.