Tachometer acting wacky

[Pstyckiewicz]

My tachometer at idle jumps around. At idle it sits at 0 then it just jumps up to 500 Rpm then back to 0. This is without hitting the throttle. I have a video but can’t figure out how to attach it.

 

[Karl kostman]

I dont know if the hummer is a mechanical tach or not but if it is detach the speedo cable from the back of the tack and put a few drops of oil into the jacket that surrounds the cable, if you can pull the center part of the cable out do so and lightly oil the entire length and it should just slide back into its outer casing. If its an electronic tack then I would detach the cable from both ends and make sure your contacts are clean and reinstall and see how it acts. If its still acting up then I would replace the RPM sensor of the portion of the tach.

 

[Pstyckiewicz]

Im almost 100 percent sure it’s electronic. I’ll will try to disconnect and clean and reconnect.

 

[springer1981]

Im almost 100 percent sure it’s electronic. I’ll will try to disconnect and clean and reconnect.

First what model HMMWV do you have? Some Tachs are run by a tach drive in the back of the engine while others are hooked up to the alternator.

 

[Pstyckiewicz]

I have an M1152A1.

 

[Mogman]

It is likely a bad connection/poor ground

 

[Pstyckiewicz]

Thank you!

 

[Mainsail]

Mine does that from time to time, but at high RPM.

Pretty low priority on the list of things to work on since I really don't look at it much.

 

[Retiredwarhorses]

Check the make sure you have the correct serpentine belt to pulley setup..a small fixed pulley with a -3 belt will slip and cause the Tach to be spotty