Scorpio Speed sensor question

Scorpio / Scorpio Cosworth Discussions - Questions, problem resolution, general talk, technical tips and modifications.
Ed Lijewski
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Re: Scorpio Speed sensor question

Post by Ed Lijewski » Tue Oct 10, 2017 12:09 pm

Most failed Scorpio VSSs I'd heard of were intact but defective internally somewhere; I have two units right here at hand like that, and Ken Kizer's photo shows his issue being internal.

Hall Effect sensors (the VSS magic, producing square waves...) do fail and sometimes without much/any warning: see EEC-IV PIP failures.

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Re: Scorpio Speed sensor question

Post by brokencase » Tue Oct 10, 2017 1:09 pm

I've searched the web...
It looks like the Ranger A4LD speed sensors (and other ford models of the same vintage) are a reluctor type of sensor.
That means they put out a sine wave (as milehighXR stated). That means more work to adapt the signal to a form that the Scorpio likes.
It's not impossible, just more work.

More than likely I will probably end up at option 3 where I open up and attempt to repair my existing sensor.

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Re: Scorpio Speed sensor question

Post by brokencase » Tue Oct 10, 2017 4:15 pm

In the archives D. Compton revealed the output of the reluctor type VSS. Only he did not know at the time the the Scorpio VSS was hall effect and had a different type of output:

Date: Mon, 16 Jun 1997 15:44:14 -0400
Reply-To: Dave Compton <DCompton@JNPCS.COM>
Sender: The Merkur Owners List <MERKUR-OWNERS@HOME.EASE.LSOFT.COM>
From: Dave Compton <DCompton@JNPCS.COM>
Subject: Vehicle Speed Sensor (VSS) Output characteristics
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

Got this info from Gary Morrell at Ford, via the EEC list.

I figured the Scorpio guys could use it for troubleshooting. XRs don't
have a VSS, hence my request about data on the VSS, for when I install the

Begin quoted data:
The VSS is a variable reluctance sensor. Its output will be roughly sinusoidal,
centered about zero volts, at 2.222 Hz per MPH. The output (volts peak-to-peak
into an 825 ohm load) will vary from approx. 0.7V at 6.667 Hz to 6.0V at 280Hz.
Minimum system load is 825 ohms, all systems in parallel, meaning that a single
VSS can drive the cruise module and the EEC speed input(s). The sensor gives 8
cycles per shaft revolution.
End quoted data:

Northern VA, USA
another piece of the puzzle

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Re: Scorpio Speed sensor question

Post by brokencase » Tue Oct 10, 2017 10:23 pm

So tonight the ballgame was rained out so I decided to do some initial exploration...
I pulled the heat shield out of the way to gain access...and then I notice something strange.

Somebody had used one of those crimp/splice things on the yellow wire on the VSS sensor harness.
They crimped in a black wire that went up over the cross member and then up to the engine bay along the firewall.

The wire does not connect to anything. It is just zip tied off up near the battery.
I suspect that somebody was having previous troubles with the VSS sensor and this was a "test line" that they could
connect a meter to.

How convenient. Haha! I'll bet this Scorpio is already on it's second or third VSS sensor!
I have a very complete service history on this car that I am going to search through to see if there was
any work related to this.

So I wiggle wires and re-seat the connector. Put the heat shield back on and take her for a spin to see if the issue
clears up. It does not.

At this point I notice leaking ATF puddle under my nearby 03' Sport Trac. Now what?
So I spent the next hour and half repairing a corroded hard line and rubber hose
going into the external trans cooler on the Sport Trac.

Making progress on multiple fronts...

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Re: Scorpio Speed sensor question

Post by blugg » Fri Oct 20, 2017 12:23 pm

ive had some sensors that Im not sure...the talented hands have passed away an never know the ways of the force.

MPM has small stash of NOS and used VSS automatic and manual trans sensors in the parts cove for those looking to stay OEM however would be priced higher than a new Contour units for those seeking originality vs cost savings. 847-688-1234
Last edited by blugg on Fri Oct 20, 2017 2:48 pm, edited 1 time in total.

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Re: Scorpio Speed sensor question

Post by brokencase » Fri Oct 20, 2017 1:01 pm

I have purchased the the Ranger two wire reluctor sensor (STANDARD MOTOR PRODUCTS SC46 - $6.95 on clearance from Rockauto) along with it's associated harness connector STANDARD MOTOR PRODUCTS HP4475.

I have made a circuit that will translate the a/c output of the reluctor sensor into the square wave output the Scorpio desires.
The Scorpio manual states all the specs I need: The VSS outputs a square wave less than .2 v and greater than 5.5v into a 680 system load.
This is confirmed by an archive post by IMON member way back who made measurements of a working VSS.

The reluctor sensor outputs the same number of cycles per rev as the Scorpio sensor, it just needs to be turned into a square wave.

The goal is to effectively put this issue to bed permanently since the reluctor based sensor is more reliable than the Scorpio hall effect sensor.
It it just magnets and coil, it will probably last forever.

I'll post the circuit here for all to benefit shortly. Sure beats hunting down unobtainium and is well under the $150 sterling for the European
aftermarket option.

"for those looking to stay OEM"? Are you out of your mind? "OEM" with respect to a Scorpio only means there are many known failure modes that must be addressed. This is one of them.

Yea, I'll go ahead and put a flimsy OEM odometer gear back in so that I keep originality...and no, I won't secure the hood release cable to the latch because Scorpio owners are supposed to crawl under and try to reach up and release the hood release. That's the original and OEM thing to do.
And don't put a relay on the defroster circuit. The OEM switch is supposed to melt. Leave the OEM cork valve cover gaskets in place also. It's not an original Scorpio unless it has the "cooking oil" smell to it.

Shall I go on?

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