ECU Tach output questions

[agent4573]

I can't seem to get any signal from the tach output on a 90' ECU. I'm trying to put in an Autometer tach and can't get it to work. I can tap the signal into one of the wires going throught the PCU and that gets the tach working, but it only supplies one pulse for every 2 revolutions, instead of the 3 pulses for rev that it needs. So basically, the tach reads 1/3 as high as it should. Do i need to put in a pull up circuit or something funny to get the tach singal from the ECU to work? The gauge will take anything between a 5-12V square wave signal. My other option was to go buy a bunch of diodes and "AND" gates and tap into every wire going through the PCU. "AND"ing all the PCU wires together will give me a square wave cycle any time any of the cylinders fire. Just looking for more options. Thanks.

[twinturbozxtacy]

pull the cluster and tap in there.... what i did on all my old fords. besides all z32 had a tach factory so why is that no good enough? if you really have a prob getting the autometer to work go with one of the new digital ones.

[agent4573]

Its in a sandrail. No stock tach, no stock gauge cluster. Even if I get a digital tach, tapping only 1 coil wire on a 6 cylinder will provide 1/6th the amount of pulses required for a 6 cylinder tach. Are the new digital ones adjustable to work in any number of pulses pee revolution?

[twinturbozxtacy]

tap into the crank sensor output? alternator maybe? oh btw those pulleys work out good for you? totally forgot you had a sand rail, my bad. as for the newer digital ones, i have no idea i was just spitballing, but they have the gauges with their own computer units now i dont see why they would not be programmable.

after a quick google
EG:http://faria-instruments.com/products.p ... 1_tachProg

[agent4573]

Ill look into tapping onto the cas. That might work. Prolly have to make a small rc circuit to condition it, but I might be able to use that. The original pulleys are working well so I haven't installed urs yet. Theyre here for backup though as I'm sure ill need em sooner or later.

For the cas, how many pulses per revolution does it put out? I would imagine that trips for every cylinder firing, which means 3 per rev right? Ill have to put a test light on it tomorrow and see

[Z31DETT]

Hey I'm running into the same problem with the aftermarket tach. If you figured out how to get it working please share!

[agent4573]

I tapped into the crank angle sensor pins on the ecu. It gives the proper 3 pulses per rev that a v6 tach is looking for. Pins 41 and 51 are connected as are pins 42 and 52. One of them pulses 3 times per rev and one pulses 360 times. I just put a test light on it and found the 3 per one and tapped in. I can look tomorrow for which is which but I cant remeber right now.

[Z31DETT]

Awesome I'll try when I get home. Thanks

[Z31DETT]

I tapped into the crank angle sensor pins on the ecu. It gives the proper 3 pulses per rev that a v6 tach is looking for. Pins 41 and 51 are connected as are pins 42 and 52. One of them pulses 3 times per rev and one pulses 360 times. I just put a test light on it and found the 3 per one and tapped in. I can look tomorrow for which is which but I cant remeber right now.

I just tried checking the wires with my test light and all it did was make the car stall. Did you get a chance to look at what wire you used?

[agent4573]

You would have to use a low power LED test light. If you used a normal incadescant light it wold draw too much current and would kill the signal going to the ecu. I'm 99% sure its 42/52 the yellow/green wire. The tach draws almost no current so yoy can use that as the tester. Hook it up to pin 52 and see if it works. Just make sure its setup for the v6 pulse count and not a v8 or 4 cylinder.

[twinturbozxtacy]

glad you figured it out!

[Z31DETT]

I got it from one of the green and black wires lol. Thanks for the help!

[agent4573]

I apologize for leading you to the wrong wire. Glad you got it working though.

[Z31DETT]

No problem. I'm just glad I got the gauge working so I can get my car on the dyno haha. Thanks again