Porsche 911 VSS not working

[ducman82]

i can't imagine the magnets being loose, or changing polarity..... hmmmm

[djb25]

Yeah, I doubt the magnets are loose. If I remember correctly, theyre epoxied into the wheel.

It's supposed to be nicer out tomorrow, so I'll be able to check the speed against my GPS.

[Dennis930]

Damion,

Glad to hear you got VSS working. And don't be alarmed if the speedometer and TS don't agree. TS will likely be more accurate. My Speedometer reads about 5 MPH faster than actual. When you rotated your wheel one revolution you should see 8 pulses as the sensor (reed switch) closes when the magnet is present, then opens as the magnet passes. But, apparently it is working. There have been some posts about one or two of the magnets coming loose and dropping to the bottom of the transmission. If this were the case TS would read less than actual, and the speedometer would also, because it is looking for 8 pulses per revolution, not 6 or 7 pulses if a magnet or two had come loose.

[Porsche930Targa]

Damion,

There is something wrong. This should work. It works fine on the my 930 transmission. Same set up. It is a reed switch. Make sure the wire that you connected in the tunnel checks out by doing this test: connect the test lead of your meter to pin 28 (MS3X connector) and connect the other lead to vehicle ground. Spin the rear tire to verify an on/off signal to ground. Make sure that the meter reads close to 0 ohms (1 - 4 ohms) and not a higher resistance. If this fails, you need to use the other wire going to the speedometer in the tunnel.

Hey Dennis which wire did you end up using brown or green?



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[Dennis930]

Damion,

You need to check which wire going to the speedometer goes to ground and which one goes to the tach circuitry. Both wires going from the tunnel connection to the speedo are red/brn, so it depends on which one goes to ground. You need the wire from the sensor(reed switch) that does NOT go to tach ground connected to MS3X. The MS3X VSS input looks for a ground pulse to trigger a count. There is a pull up resistor in the MS3X VSS circuit that creates a 5VDC signal, but when the reed switch makes it causes a ground on the VSS input which drops the 5 VDC signal to zero which is one pulse. If you have the wrong reed switch wire connect to VSS it will see a ground all the time and will not work.

[ducman82]

what settings, lag etc are you using? i have mine "working" but the speed jumps all over the place...... is somewhat around the actually speedometer...... but will double some times in a flash.