240sx w/sr20 RPM gauge won't work!!! Help!!

[Koto 307]

Hello,
I have a 95' 240sx with a sr20 motor swap...Today I went down to the car wash, and after I was done cleaning my car, I got in it and started driving back home. Shortly after leaving the car wash I noticed my RPM gauge was going crazy!! It kept jumping all over the place from about 2000-8000 rpm's and it did this numerous times before it completely stopped working.. So now when I start my car, the RPM needle sits at 0 rpm's and then I'll continue driving and after a while the RPM needle will start going crazy and jumping all over the place again, but after about 30 seconds to a minute or so, the needle just dies and falls back to zero... Please help!!! If anybody has any ideas, as to what could be causing this to happen please let me know!!! I've had the car for over 2 years and this has never happened before....

[Hijacker]

If the car isn't acting funny (drivability-wise), then the issue is with the either the tach or the ECU.

I would first say try reseating the CAS plug in case it came loose. The ECU takes the signal it gets from the CAS and then relays it to the gauge.

After that, check your grounds and make sure a bolt hasn't backed out and causing funky voltage spikes or something. The big ones to worry about are the grounds near the ECU and near the gauge cluster. Grab the FSM and look for where they're anchored to the chassis in the EL section.

Last, check the ECU is putting out proper voltage to the tach. The higher the RPM, the higher the voltage should be. If you're getting consistent voltage based on the motor's RPM, replace the tach.