Greetings,

I'm wondering if anyone knows what kind of signal the tach in the factory cluster takes? I swapped to an aftermarket ECU and have all the other gauges running but the tach is weird. The ECU I'm using has a 12v tach output. I picked up the tach input at pin 10 (white) on the ECU. It drives the tach but the tach reads high. When it's idling (800 or so rpm) it reads like 1500. I'm assuming it is frequency that drives the tach as opposed to amplitude on the voltage. In other words I can't use a resistor on my output to dial my tach in. Thoughts?

 

Another question that applies to my ultimate solution for this problem: Does anyone know how the factory ECM provides a tach signal on that #10 wire? I'm assuming that it uses either the crank or cam sensor to generate the signal it provides to the tach on that wire? Do you need both? Or if I feed the ECM a crank signal will it calculate rpm and provide the signal? Or does it use a mix of sensors?

 

Ok, so here's what I've tried so far (and btw, I'm going to figure this damn thing out lol): I ran my 12v tach signal from my standalone ECM out to the input on the back of the gauges (wire 10 at the ECM, white in color). The tach works but reads a percentage high. Next, I used my lingenfelter box between the cam and crank sensors to feed the stock ecm a 24x/1x signal and reconnected the tach to the ecm. This didn't work either. So now I'm thinking the ECM needs some other input to generate the tach signal or the lingenfelter box needs something more to provide the output signal. Tonight, when I have a helper I'm going to see if the lingenfelter box syncs when the truck is running. If not, the problem is the box/inputs to the box. If it does, then the factory ecm needs something else to generate the tach signal. Thoughts?

 

Please update with your findings, I have a tach issue to resolve as well. Mine is not functioning at all after a Terminator X install, even with the VSS splitter on the trans.
Good luck.

 

I talked with this guy : https://technoversions.com/TachMatch.html . He said the tach output to the dash from the ecm is 4 cylinders (1/2 what the Aces puts out). I checked and the dash does show twice the rpm as the engine is actually running. I'm going to install the tach match and that should fix it.

 

Yep, the tachmatch worked perfectly. Plug and play. I hooked it to 12v switched off my new ECU and then cut the tach wire going to the dash. Hooked it up to the input/output and tach works perfectly.