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

1. Use a pull-up resistor (1K is fine I guess) between the signal wire and 5V (is it really better to use 5V than 12V? Why?) to get a typical 0V-5V-0V-5V-... square wave.

This is what i done on my mates schirocco vr6 using hall sensor input. Vr6 engines have two versions of hall sensors one using 12v power and one with 5v. Earlier obd1 engines have 12v. I was having thouts about using 5v puling suply but evrithing works fine. we have only dwell issues. After setting dwell to 1,6 engine revs frealy trough entire rpm band.

Due to the date on this, I am sure you have already worked through the problem and are driving around, but just for everyone's future benefit:

I believe it is a much cleaner install to reverse the opto circuit on the MS board rather than use a pullup resistor. Basically, you are already building the MS and have to use some jumpers to select your ignition configuration, just use those two jumpers to reverse the circuit!

"optoin" jumpered to "S5" (which is a fused +5v source found immediately next to the db9)

"tachselect" jumpered to "XG1".

And of course, "optoout" jumpered to "tsel"

Reversing the circuit is cleaner than using a bandaid like a pullup resistor, though if you did use one I am sure it works fine. There are many different ways to cook chicken

a mallory technician just informed the 6100m hall sensor used in their distributor must see a range from +12v to -2v to properly signal the distributor, he also said this hall sensor will not work with an ecu and either the 77201 excell or 1255104 mallory distributor must be used with ecu controlled fuel injection systems,
the cover statement in this thread mentioned using a 2k2 pull up res to 12v, does this mean 12v will go to the hall's negative side and is this via s5 from the relay board? the 5.5v coming out of the ms2 3.57 board via relay board s5 doesn't appear to allow this 6100m hall sensor to function properly,
this particular ms2 3.57 ecu was sent back for warranty repair in 2010 and at that time it was confirmed to be wired properly to work the mallory hall sensor, this is the first try since then to get it this system working again,
tia, kevin

that should read signal the coil not signal the coil

All respect to the tech's experience, but I'd be surprised to find a Hall sensor in a distributor that couldn't be made to signal something as flexible as a MegaSquirt. He may have meant that the 12v signal couldn't be used directly with an ECU expecting +5v; I'll agree with that part, but that is why the Opto circuit is there.

S5 is a 5v source only. There are two +12v sources on the V3.0 and V3.57 board, S12 and S12c.

DonTZ125 wrote:All respect to the tech's experience, but I'd be surprised to find a Hall sensor in a distributor that couldn't be made to signal something as flexible as a MegaSquirt. He may have meant that the 12v signal couldn't be used directly with an ECU expecting +5v; I'll agree with that part, but that is why the Opto circuit is there.

S5 is a 5v source only. There are two +12v sources on the V3.0 and V3.57 board, S12 and S12c.

a 300 ohm pull up resistor brought the 12v hall power supply down to the 9v needed on the hall trigger side so now a good signal is sent through the tach wire to relay board s5 and the ecu optoisolator,
s5 now signals the coil allowing a nice spark out of a test plug, the dispaly tach responds and trigger wizard show ignition advance as a drill motor spins the mallory dizzy, yea

the bench test before this was on the injectors using alpha-n and that appeared to work also so maybe it's time to throw the parts on the engine