i was on the highway today at about 70mph and i noticed that the tach was at about 2K rpms, not up at about 3K where it should be.
i kept my eye on it for a minute and i quickly jumped up and down a couple hundred rpms a few times, but thats it.
i slowed down and brought it out to vtec in 2nd gear, and the tach seemed to be right on cue for the vtec engagement.
later on the way home it was back to normal.

any ideas? d16z6 @ 200K miles.

 

Sounds like your VSS is on its way out, inconsistency is the first sign.

 

oh plus it was raining.
whats replacing the VSS involve?

 

whats vss?

 

vehicle speed sensor, but that relates to the speedometer, not the tach. i'd check the ground but really i wouldnt worry about it too much, mine bounces a little now and then. is your tach aftermarket or in the cluster?

 

I didnt mean VSS, I dont know why I saw tach but thought speedometer. it does sound liek a grounds issue.

 

Yea that was what mine was when i called autometer

 

either that or his tach has just pooped out on him. His car has some high miles on it.

When I got my car dynoed, mase told me my tach was off, 6700rpm was actually 8K!!! I got another gauge cluster but haven't put it in yet, hoping that fixes it.

 

check your grounds

 

Check your distributor, last time I had the same issue and my distributor bolts were loose.

 

the vss thing was why i was confused about the tach being affected...
anyway yeah the tach is in the cluster (92 si), what grounds should i check? the only one i know of off hand is the battery one and the valve cover one. is there one for the ecu?

 

I've heard of a bad ignitor in the distributor giving off wacky tach readings after it gets hot. You may want to check out the ignitor, and see if replacing it helps with your problem...

 

check your thermostat ground and transmission ground

 

when you check your cap and rotor look at the contact points, i had the same problem with my tach and it bounced all over the place. it ended up being corroed and worn out points that just flaked off.