how is the tach set up on a 924s

probuild521 · 07-07-2009, 04:08 PM

there is a piece that goes on to the bell housing that i believed to be part of the tach, i hooked it up to the only wire that made sense but the tach didnt work, does it measure spark like some do and i actually need an internal combustion engine to make it happy or what?

idontknow · 07-07-2009, 05:45 PM

Quote:

Originally Posted by probuild521

i actually need an internal combustion engine to make it happy or what?

Hate to point out the obvious but the tach does work best when paired to an internal combustion engine.

The tach is designed to count the sparks from the coil and is driven usually at 12v. The 2 sensors you believed could drive the tach can't.

What kind of alternative engine are you using?

probuild521 · 07-07-2009, 10:08 PM

Quote:

Originally Posted by idontknow

Hate to point out the obvious but the tach does work best when paired to an internal combustion engine.

The tach is designed to count the sparks from the coil and is driven usually at 12v. The 2 sensors you believed could drive the tach can't.

What kind of alternative engine are you using?

its an electric motor, i thought i read somewhere that it counted flywheel rotations, guess im wrong need to now look into another way of hooking up a tach

944 Ecology · 07-08-2009, 04:23 AM

Actually, it does, but that work is done by the DME, which then calculates when to send pulses to the ignition coil. The tach merely receives those pulses from the DME and indicates the rpms.

So, while there are pulses coming from the flywheel sensors, it doesn't convert to the tach signal directly, and, oh, by the way, the tach pulses are about 12 volts DC and the flywheel sensor pulses are about 1.5 volts DC.

probuild521 · 07-08-2009, 08:38 AM

Quote:

Originally Posted by 944 Ecology

Actually, it does, but that work is done by the DME, which then calculates when to send pulses to the ignition coil. The tach merely receives those pulses from the DME and indicates the rpms.

So, while there are pulses coming from the flywheel sensors, it doesn't convert to the tach signal directly, and, oh, by the way, the tach pulses are about 12 volts DC and the flywheel sensor pulses are about 1.5 volts DC.

is anyone aware of a way to keep the stock tach and utilize this sensor to work for my application?

944 Ecology · 07-08-2009, 08:41 AM

Well, you might continue to use the DME computer to convert the flywheel pulses to an ignition coil signal, but it seems like a lot of extra weight.

It would be simpler to have an rpm indicator from the electric motor.