Tach not working,,, What to check?

[Trex]

My tach quit working, what can i check for? Truck shifts hard and no o/d light comes on but i can tell it works, just no light comes on to let me know.

 

[Cubey]

The tach sensor on the top of the gear cover in front of the IP. It has 2 wires.

 

[hesutton]

The tach sensor on the top of the gear cover in front of the IP. It has 2 wires.

X 2.

It happens. Not unusual. Think I've had to replace the sender on both my IDI's in the past.

Heath

 

[Trex]

is there a way to check it?

 

[Cubey]

is there a way to check it?

How does it look visually at the wires entering the sensor? They get damaged at that spot more often than not.

the tach sensor is a AC pulse, you measure it with a multimeter set to AC volts, unplug the sensor and start the truck, with it running touch the leads to the sensor wires, you should get a reading around 2.5 V AC if the sensor is good. most of the tach issues are ground related. the clusters have circut issues in them also.

there was a typo in the voltage number, good sensor at idle is .25vAC. voltage at 2000 rpm is about 1.5vAC. at 3000rpm it is about 2.5vAC. this is the results of a proper working tach sensor, sorry for the typo and error in info. when testing the voltage at idle, the reading should be constant and smooth and increase constant and smoothly with RPM's

From this thread, might wanna read through the whole thing, it has lots more info:
https://www.oilburners.net/threads/testing-a-tach-sensor-and-or-gage-harness.54186/

 

[dgr]

Doesn't his tach signal come from the PCM for his year? Sensor sends signal to PCM. PCM sends signal to the tach. If not, ignore me.

https://www.oilburners.net/threads/under-hood-fuse-box-diagram-93-idi.71378/

Maybe it's electrical. I'd check fuses etc per the last post in that thread.

Oldbull posted some test info on this thread. https://www.oilburners.net/threads/testing-a-tach-sensor-and-or-gage-harness.54186/page-2

You should see rising AC voltage from the sensor with an increase in RPM. Disconnect it and hook a digital meter to it. Wish I could provide more info. You're reading a variable Hertz signal with a meter made for 60hz. Each meter will read different but should increase with rpms.

 

[Cubey]

Doesn't his tach signal come from the PCM for his year? Sensor sends signal to PCM. PCM sends signal to the tach. If not, ignore me.

Oh, could be. I've had newer than an 87 IDI, which doesn't even need a tach sensor to operate. (C6, all vac operated). My RV has a place for the sensor, but it has a plug in the hole, since van clusters pre-92 never got a tach.