Hi guys,

I'm having an issue with my ct9a where the rpm needle will bounce around, the engine idles and revvs fine but the tacho is doing its own thing. Has anybody had this issue,

I'll attach a vid of my car doing it. I was stationary and in neutral in the vid.



Cheers

 

Might be a cluster mechanism issue. Substitute good known cluster

 

Thanks for the reply, is this something I can change on my current cluster as I don't really wanna change the whole thing. Also this issue only started since I have been cleaning things in the engine bay.

Is there a rpm sensor or a vacuum line that reads the rpm?

 

I've seen this before on cars that have bad alternator diodes. The AC frequency from the alternator can affect the speed sensor if it absorbs it as "noise".

Disconnect your alternator control wire and see if it still does it. Your car will not charge the battery but who cares if it's only for testing.

 

Thanks for the reply, sorry I forgot to add that this is an intermittent issue and doesn't happen all the time.

Cheers

 

if u have a friend with an evo, try switching clusters.
atleast the result will point u to a more specific direction

 

Ok so an update for you guys, i have changed the cluster to a known working one, and the problem still persists.

Don't Evo's get the rpm in this order, crank and cam sensor - Ecu - Dash, i wasn't aware that a speed sensor sent rpm readings, i could be wrong though.

 

okay, thats great news coz clusters cost a lot.. try this 👆🏻?

 

ok very noob question incoming.

but what is an alternator control wire? it may be referred to something else where im from.

 

There are several wires on the alternator. The control wire is not the big beefy one. You should have a little plug, temporarily disconnect it and see if you get the symptom while it's disconnected.

 

So I tried unplugging the alternator and tried changing the speed sensor in the gearbox and got nowhere, any more ideas?

 

Connect an external tach to the tach port in the under hood fuse box and see the same fluctuation occurs.

 

The signal comes from the coils.

 

Forgive me to revive this post. I got exact same problem, anyone knows the solution?

 

Hey mate, it ended up being a dodgy Scotch lock in the ECU wire for the rpm, I just looked up a wiring diagram from m for my Evo I can't remember if mine is 3 or 4 plug but you should be able to find either. Haven't had an issue since.