How does the tach work?

[Legacy777]

Pretty sure the tach is one pulse per revolution. I tied into the tachometer output signal at the ECU for the wideband and did not have to modify the signal to show the correct RPM.

Just a question. How are you going to correlate engine RPM to vehicle speed if you have different gear ratios.

Or when you were talking about rpm, were you referring to driveshaft RPM?

[vrg3]

Ah, cool, that confirms what I thought. Unless you had to tell your wideband that it was hooked up to a 4-cylinder 4-stroke engine?

We're talking about hooking a driveshaft RPM pickup to an OEM tachometer with a different face.

[Legacy777]

No I'm pretty sure I just hooked it up.

[BAC5.2]

It's super ghetto rig, but it's what needs to be done when there is no speedometer scroll on the 3/4 gear.

I'll let the ECU think it's got some ghetto signal.... unless I could use the speedotachometer to spin the stock speedometer gear (including the VSS)?

Would THAT work?

[vrg3]

Nothing spins inside a tachometer, I don't think.

I think you should just start with 5 magnets and two pickups and see how things go.

[BAC5.2]

I most certaintly will! As long as it doesn't throw a check engine light, I'll be happy. And it would be great to be able to know how fast I'm going too!

[isotopeman]

Didn't we determine that if you put 16 magnets on the driveshaft the VSS would be about right?

For some reason, I was thinking four. I'd believe you over what I come up with any day though.
So how many magnetic points are there on the magnetic rotor in the VSS2? Does anybody have one out or have a picture of one? Wouldn't that tell us exactly how many times it would have to switch per revolution for the vss signal? (assuming the cable makes one revolution per axle revolution)
As for the vss pickup, are there only two or three leads? You mentioned that one is grounded, and another to the VSS input of the ECU, but where does the 5V power source come from?

[vrg3]

I seem to remember the VSS pulsing four times per wheel revolution. If the final drive ratio is about four, that would mean it would need to pulse 16 times per driveshaft revolution, right?

The stock VSS is built into the speedometer. There's only one lead going from the speedometer to the ECU. The VSS alternately grounds and ungrounds this wire.

The 5-volt supply is inside the ECU.