scarecrowX

just use a darlington pair to yank the MSD's trigger to ground.

http://web.archive.org/web/200510170...torReplacement



the bigger transistor has to be able to pull about 500mA to get it to ground, since the MSD uses a pretty low-ohm pullup resistor on that line.

boarder360j

I keep hearing about this darlington pair that you can make but the only info I can find is the link you posted and that diagram.

Does it take place of the igniter or do you still keep the igniter hooked up like normal when using this?
Is the yellow/green coming from the ecu in that diagram normally the wire that gives the igniter its signal?
Do you have a picture of one complete or any more instructions?

I found this site which gives a clear discription of how the igniter functions. http://www.tegger.com/hondafaq/ignit...ion/index.html

From what I can tell this honda to msd trigger adapter looks the same as the stock igniter ciurcut but without the control chip. So I dont get it, whats the advantage?

scarecrowX

the honda igniter has current limiting. the control chip uses a sense resistor on the coil line to determine current flow through the coil and limits it to a specified value to prevent the coil/igniter from burning out. it also has a lock prevention circuit. if current flows through the coil for more than a specified time value, it shuts the igniter down slowly to prevent the igniter from burning out and to prevent an unwanted spark.

the circuit i posted takes the place of the igniter. that circuit accomplishes 2 things:

-pulls the MSD trigger to ground, then releases that ground to fire the MSD.

-provides 12V pullup to the IGT line in the ECU to prevent ECU CEL code 15.

i used that circuit diagram to figure out the honda's firing signal for running a honda P75 on my MR2/3SGTE. the circuit works. i modified it to send a 5V trigger to the MR2's igniter, since the MR2's igniter is higher energy and has intelligent internal dwell control, but the circuit is almost identical. it's not bulky, it's 3 resistors and 2 transistors (or just one transistor if you use the right kind of transistor. an LM395 NPN would work (and you can get free samples from www.national.com. just use the pullup resistor to 12V on the base of the transistor and connect the collector directly to the MSD trigger. they're ultra-reliable and can sink about 500mA.