VEHICLE SPEED SENSOR Output Signal - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 9 Old 12-10-2001, 11:40 AM Thread Starter
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VEHICLE SPEED SENSOR Output Signal

Anyone know what type of signal the VSS puts out? Of the two wires, one seems to be grounded, so the other should be a square-wave voltage? Or is it a varying resistance that the EEC converts to a voltage internally?

I ask, because I need to tap off of this to get a signal for my electronic speedometer.

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-Neil.


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post #2 of 9 Old 12-10-2001, 01:33 PM
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It's not a resistance. The best I can figure, is, it's a magnetic pulse switch. I know that it sends "pulses" to the computer and/or dash, but that's the extent of my knowledge.


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post #3 of 9 Old 12-10-2001, 01:57 PM Thread Starter
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Yep, should be a pulsing (squarewave) positive voltage, but if only 2 wires, and one wire is grounded, I don't know where it would get the positive voltage to send to the EEC.

Arrggghhh -- I need a freakin' oscilloscope!!!

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post #4 of 9 Old 12-10-2001, 02:39 PM
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I believe it is a hall-effect sensor.


on the topic of the VSS, does anyone know what the PCM in a Mustang 5.0L does with this signal? Does it use it someway to control the idle or IAB? REason I ask is that I have a strange bucking, stalling problem when engaging the clutch in 1st or second at low speeds... its intermittant and if I let the clutch out very slow, such that the clutch slips and moves the car forward, the problem does not occur. I wonder if the VSS is screwy and telling the motor to idle rather than holding the rpms higher for the shift?

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post #5 of 9 Old 12-10-2001, 03:44 PM Thread Starter
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But what type of signal does the hall-effect sensor put out?

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on the topic of the VSS, does anyone know what the PCM in a Mustang 5.0L does with this signal? Does it use it someway to control the idle or IAB? REason I ask is that I have a strange bucking, stalling problem when engaging the clutch in 1st or second at low speeds... its intermittant and if I let the clutch out very slow, such that the clutch slips and moves the car forward, the problem does not occur. I wonder if the VSS is screwy and telling the motor to idle rather than holding the rpms higher for the shift?
Absolutely -- and that is exactly what I am trying to do -- since I'm using an electronic speedo, the sender replaced the VSS in the tranny. I got the car tuned nicely with the 36# injectors, but now with 42# injs, it does the same things you describe. I could try and mecahnically mate both of these, but I'm also exploring the use of the VSS signal to drive the (programmable) elec speedo.

Run your codes -- you would get a 29 if the VSS is toast.

Cheers,
-Neil.

- Shelby Cobra kitcar, 5.0 supercharged.
- Fox coupe with 4.6 DOHC project in progress.


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post #6 of 9 Old 12-11-2001, 01:25 AM Thread Starter
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Got a little be experimentative just now. Found out that the VSS really IS a Hall effect sensor, so I put the VSS tip in a drill, and the output on a VOM (set to AC, 50V). From zero to full speed, the voltage varied from 0 to 10V and seemed to be proportional to the drill RPM. I'm sure it will go higher with a faster drill. Wondering if the voltage may be too low at low speeds to drive the speedo. Speedo may show 0 MPH until vehicle gets to a certain MPH and then just jump to show that speed. Also need to know how the VSS rpm correlates to vehicle speed. That way I can figure out max voltage from the VSS so I don't damage the speedo.

I may need to build an isolator circuit to clean up the signal for the speedo, but I can't remember that much electronics.

Getting closer.

-Neil.

- Shelby Cobra kitcar, 5.0 supercharged.
- Fox coupe with 4.6 DOHC project in progress.


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post #7 of 9 Old 12-11-2001, 01:46 AM
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Neil,
I read that the VSSm generally, come in two types... one type converts the AC output to DC within the VSS itself...some sort of buffer. The other type does not, but the PCM does it. Either way since PCM's cant process AC the signal is converted to DC. I also read that on many vehicles using a VSS, the PCM is set to ignore low speed/low voltage input...like 3mph or lower. I suppose if you drive a electric speedo off the VSS you may need to do this, but I'd expect the speedo manufacturer to tell you so.

Anyway I bought a new Ford VSS today and installed it. I am hoping for a huge miracle in that it resolves my first gear buk/rpm drop/stall problem.

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post #8 of 9 Old 12-11-2001, 02:00 AM Thread Starter
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67Stang -- keep me posted on how the car behaves after the switch.

BTW, the speedo mfgr didn't want/expect me to use the VSS signal -- they were quite unhelpful from that perspective. They sold me a special sender that replaces the VSS. My prob is to get both in there simultaneously. Either electronically, or mechanically.



Cheers,
-Neil.

- Shelby Cobra kitcar, 5.0 supercharged.
- Fox coupe with 4.6 DOHC project in progress.


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post #9 of 9 Old 12-11-2001, 09:15 AM
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The VSS is not a hall effect sensor. It is a Magnetic AC pulse generator. It will produce an AC sine wave pattern when viewed on an ossiliscope. A hall effect sensor produces a square wave pattern/ on-off-on-off varing frequency. Quick check : 2 wire magnetic sensor, 3 wire hall effect like in EEC IV distributor.
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