[VeeDubber]

Hi folks,

I have an autozone RPM gauge. It gets signal from the diagnostic port next to the fuse box for several years. It's a 22RE manual with 119k mi.

Recently the RPM needle jumps erratically over the RPM range. Mostly happens at 1st cold start of the day or sometimes during the day even after warmed up. Could this be a electrical only issue? For example, I am positive the engine is not running at 4k ~ 5k RPM at 60MPH with 5th gear...because engine still sounds running at ~2.5k.

Where should I diagnose first?

 

[Jayota]

Try cleaning the ground for the ignitor. Mine was dirty and the tach would tell me the truck was at 0rpm at idle.

 

[kamesama980]

could be the high quality autozone gauge too. not that I should talk mine still works 3 cars and 7 years later.

 

[Vicoor]

Check the wiring to the gauge. The tach signal at the diagnostic connector is tied to the negative side of the coil, and if there were something wrong with the signal, then you would likely have a driveabilty issue and/or a check engine light.

check the power and ground supplies as well as the tach signal wiring.

Hope this helps