Getting Autometer Tach to work..MSD GMR Pickup

[~KnuckleDuster~]

Ok. I've been dealing with no tach's in RB's since 2008 and it's getting old. I originally bought an MSD tach adapter to try unit I read about it poping the resistor in the ecu. I tried wiring in the 10k resistor between the signal wire and 12v power (i think that's what it was) and nothing there. I found one thread where a guy successfully used this MSD GMR pickup and it's the closest I've been to getting a working tach. It clamps to the coil packs power supply and sends the signal to the tach. I've got it clamped to the same big white wire you would use for your timing gun. The tach is moving but it get stuck and fails to drop and will freeze in place. Directions state for distributerless coild packs set the tach to 1 pulse 4 cyl. mode. I've tried both 1 and 2 pulse 4cyl. modes on the dip switches and nothing. Can anyone help me along? I feel like I'm so close!

 

[Wizzurp]

Man I used a cheapo autogauge tach with a 10k pullup and my rb has been showing rpm since I stuck it in.

[Vandergriff84]

I used the resister method as well and I haven't had any problems. Is it possible you have a bad tachometer?

[~KnuckleDuster~]

I used the resister method as well and I haven't had any problems. Is it possible you have a bad tachometer?

I doubt it, it's brand new. Maybe I had the wrong signal wire from the get go when I had the resistor wired in, I'll have to double check the pinouts. It just bugs me that I can get this MSD unit to work that's designed to send the proper signal to a tach. It even has directions for a distributerless engine with coil packs.

 

Edited July 17, 2016 by ~KnuckleDuster~

[Vandergriff84]

I can't speak for the MSD unit but I will say that I have never been able to get a clean signal off of the white wire on the back of the coil pack harness. When adjusting timing I have always had to use the spark plug wire between the coil and the plug. I even have a newer style timing light and every time I pull the signal from the white wire I get a random flash and the RPMs on the light are all out of whack.

[~KnuckleDuster~]

I can't speak for the MSD unit but I will say that I have never been able to get a clean signal off of the white wire on the back of the coil pack harness. When adjusting timing I have always had to use the spark plug wire between the coil and the plug. I even have a newer style timing light and every time I pull the signal from the white wire I get a random flash and the RPMs on the light are all out of whack.

I've come to find out the new digital timing guns don't work on that wire too. You need an old style one. I bought a standard cheapo light for $30 and it works just fine.

Edited July 18, 2016 by ~KnuckleDuster~

[Wizzurp]

I've come to find out the new digital timing guns don't work on that wire too. You need an old style one. I bought a standard cheapo light for $30 and it works just fine.

Same, the cheapo ones work great on the timing loop

[mtnickel]

The signal out of the ECU is going to be far better than the adapter signal on the white wire.

I even got my stock tach to work with an adapter I made. It uses the ECU's signal to trigger a Transistor to give a voltage spike through a small relay coil. You shouldn't need all that however and should just need  a 12v Pullup. The stock ECU sends out a digital signal that is open(not connected), then ground, open, then ground. So not a square wave, but becomes a square wave if you use a pullup. It then outputs 12v when it would have been open, but still outputs ground when the ECU goes ground (since the likely internal resistance of the output is much lower than the pullup resistor resistance).

 

If you need help with wire colors and diagrams, let me know.

Edited July 19, 2016 by mtnickel

[Wizzurp]

Hrm, I ran a line straight from the ecu tach output to the tach input and ran a 10k resistor between the tach input line/ecu output and the 12v source for the gauges power/lights. It has worked fine since. Just had to set it up for 6cyl.