Help sharing rpm signal between MS and stock ECU

annoyingrob · Post by **annoyingrob** » Wed Jul 26, 2006 12:26 am

Here's the deal, I have a MSII v3 what I'm attempting to wire into my car to run fuel only. I'm keeping the stock ECU to control things like the AC, speed sensitive power steering, and the 6 cyl COP ignition.

I need to share a bunch of signals between the ECU , and MS, like the O2, coolant temp, air temp, and RPM. I've successfully shared all of the signals except for RPM....

The ignitor in my car that fires off the 6 coils will send a signal back to the ECU indicating that the ignition was successful. This would be a 5v square wave signal. I'm trying to use this signal for RPM, as it should provide the right signal, and I won't have to worry about trying to decode my dual wheel nippon-deno system. With a multimeter, I can see a voltage of about 4.6v at idle, which I would assume would be about right for a fluctuating 5v signal. When I hook this signal up to another input, like coolant or air temp, I can see the temperature bounce around, indicating that there is indeed a signal there

But, when I plug the signal into RPM, I get nothing. In fact, the engine dies, which I would assume means that MS is pulling the signal either up, or down to a point where the stock ECU cannot read it, and stalls the engine. I tried placing a 1k resistor inline with the signal, but it didn't help.

I can get a good RPM signal on the stim, so I know that the MS board is good. What could be causing this? What should I try to get a usable signal?

BTW, not that it's terribly important, the engine is a Toyota 1JZ-GTE

annoyingrob · Post by **annoyingrob** » Wed Jul 26, 2006 4:32 am

Ah, well I did a little more research, and I think I can just tap into the tach signal coming off the ignitor, much like what people with 3S-gte engines do.

Ferret · Post by **Ferret** » Wed Jul 26, 2006 8:48 am

If you try the first method again or if the engine dies when you tap into the tach wire, try wiring a resistor between MS and ECU.

Avner.

JustinL · Post by **JustinL** » Wed Jul 26, 2006 11:22 am

Ferret wrote:If you try the first method again or if the engine dies when you tap into the tach wire, try wiring a resistor between MS and ECU.

Avner.

This was the solution that worked for me. 1K wasn't enough and it took some trial and error to find a resistor that both my stock bosch motronic and MS2 could agree on. Turned out to be a 1.2K 1/4 watt resistor was the trick.

annoyingrob · Post by **annoyingrob** » Wed Jul 26, 2006 3:25 pm

Ok, I used the tach wire, and placed a 4.7k resistor inline with it, and it works perfectly. I'm happy now.