Rev counter

[sultan]

What makes a wrx rev counter work?

[Swindog]

Your right foot ;D

[sultan]

Lol not at the moment it doesn't. Until i fix electric issue

[DRFVDR]

At a guess it would get its feed from the ECU

or a coil pack

or the crank angle sensor

or the cam angle sensor

i know not much help

[sultan]

The feed comes from the ecu as far as i know, but what feeds that is the question. My car appears to have either a dead altenator or failed voltage reg and Im pondering that the simultaneous failure of the rev counter is related

[DRFVDR]

some vehicles rev counters get their pulse from the alternator, so it could be the issue ?

[sultan]

That's what Im hoping. Or the incorrect voltage the car is currently running has messed with where it does get its reading

[Wiretap]

All subaru tachometers recieve their signal in a 12v square wave, 50% duty cycle form from the ECU directly

[sultan]

ok that sounds confusing. are you saying there isn't a sensor or signal from some other component, but the ecu is aware of rpm change some how through the power itself? if so, surely that would be reliant on alternator?

[Wiretap]

Whut?

No. The ECU deduces the RPM from the various positional sensors, it then produces the waveform that goes to the instrument cluster... nothing to do with the alternator.

[Swindog]

I know that the rev counter I hooked up in the van.came from the top of the dizy. I needed a wee converter to change the wave form as wire tap suggests so my guess is the ecu picks up the signal from tps and electrical diz and converts it. Hopefully you have a diz and not coil on plug.

[sultan]

 Wiretap said:

Whut?

No. The ECU deduces the RPM from the various positional sensors, it then produces the waveform that goes to the instrument cluster... nothing to do with the alternator.

ok...so your first post was basically a confusing way of saying "it gets its feed from the ecu", which i've already stated i am aware of. "various positional sensors" - is what i am trying to find out.

[sultan]

 Swindog said:

Hopefully you have a diz and not coil on plug.

coil on plug is the old style right? i have that

[Swindog]

i wouldn't say old but yeah 8)

[Wiretap]

No such thing as an 'electrical dizy'... that's a coilpack, no 'signal' comes from that, the only thing it has in common with a distributor is the fact it has multiple plugleads coming out of it.

The sensors are the cam and crank angle sensor, your engine won't run if either are non-functional. If your alternator and dash gauges are not working check your fuses, the alternator is dependant on the battery lamp on the dash working, if it isn't, it won't charge.

[Swindog]

Ah yeah hiaces have them. They also have a signal output wire.

[Wiretap]

http://en.wikipedia.org/wiki/Ignition_system

What the hiace most likely has is a conventional distributor, the 'signal output wire' will just be a wire connected to the coil negative (in this case I'm guessing the coil is in the distributor), which is traditionally what has been used on non-EFI cars to drive the tacho.

There would be no point to an 'electronic distributor', that's a lot of trouble for a manufacturer to go to instead of using the ECU to control the ignition timing.

[Swindog]

That's the one. Had to have a converter on that wire for pick up. Worked well.