I noticed when I was driving today that my tach would bounce all over the place and my truck would shudder. I was on the highway about 60-65mph. It would do it for a couple seconds and stop for a min or two and start up again. If I’m not mistaken the tach receives a signal from the PCM which gets its signal from the crankshaft position sensor. So I crawled underneath it and saw that sensor was completely caked with grime and all kinds of nasty crap. So I cleaned it off and saw that the insulation around the wire was completely gone exposing the bare copper. I unplugged the connector and gave it a good cleaning and wrapped the exposed wire in electrical tape real good. I went ahead and cleaned plug on the sensor itself as well and it seems to have fixed my issue. I’m trying to figure out what would cause it happen in the first place. My best guess would be maybe the exposed wires were arcing between one another which was causing my tach to go crazy. Cause it never threw any trouble codes. That’s why I don’t think the sensor is bad. Anybody else have a similar issue? What did you do to fix it?

 

I've had crank sensors go bad on other vehicles, and an erratic tach was one symptom.

I think you might have fixed it by repairing the wires. It's probably a 5v reference signal or something, and it doesn't take much to mess it up. Hopefully it stays fixed

 

I ran fine this morning on my way into work so I assume I fixed it as well. I have a bad habit of firing the parts gun at my vehicles when they break lol

 

I've done that myself a time or two lol. That's an expensive way to fix things, though