R4PT0R

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

4b11slayer

Might be a cluster mechanism issue. Substitute good known cluster

R4PT0R

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?

Jp7

iTrader: (11)

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.

R4PT0R

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

Cheers

TariqEvo

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

R4PT0R

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.

TariqEvo

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

R4PT0R

ok very noob question incoming.

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

Jp7

iTrader: (11)

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.

R4PT0R

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

barneyb

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

RightSaid fred

The signal comes from the coils.