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.

YMMV
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brokencase
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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.

brokencase
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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
TC EEC-IV.

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:

Dave
DCompton@JNPCS.COM
Northern VA, USA
another piece of the puzzle

brokencase
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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...

blugg
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Re: Scorpio Speed sensor question

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

ive had some sensors repaired....how?? 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.

blugg@msn.com 847-688-1234
Last edited by blugg on Fri Oct 20, 2017 2:48 pm, edited 1 time in total.
Jeff

brokencase
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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 1.5 v and greater than 5.5v into a 600 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?
Last edited by brokencase on Mon Oct 30, 2017 7:30 pm, edited 2 times in total.

brokencase
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Re: Scorpio Speed sensor question

Post by brokencase » Sun Oct 22, 2017 7:23 pm

Once again I love it when a plan comes together.
I installed the new SC46 sensor and associated "adapter circuit" today and it appears to be a success. Drove the car around several miles tonight and no issues. Took it up to 70mph.

Let me start with the circuit. I can't take full credit for this. A while back an electronics magazine "Silicon Chip" did an article on a DIY MSD ignition circuit. In that article there was an optional circuit to use a reluctor based distributor input (instead of points). I borrowed this and added the power FET output and altered some other resistor values. Overall I would probably say the circuit is a bit over designed. It is probably possible to design a circuit with less components, but I wanted to stick to something I had high confidence would work.

Zener diode D1 is a 5.1 v, and zener diode D3 is a 15.1V. C3 is a polyfilm capacitor. I used 1uf because that is all I had. But a larger (10uf) would be better. It must be poly film because the whole circuit gets potted into epoxy and you can't pot an electrolytic.

The Vrms source on the left represents the reluctor sensor. The signal output is R11 on the right.

I lowered R3 in the circuit to 25k. In mine it is 33k and the circuit will not trigger well at slow rotation of the reluctor sensor. So the speedo needle won't move until I get above 10 mph or so then it "jumps" a little. Nothing I can't live with. Lowering R3 should take care of this issue.
vss_circuit.jpg
vss_circuit.jpg (46.28 KiB) Viewed 217 times
Last edited by brokencase on Mon Oct 23, 2017 8:41 pm, edited 2 times in total.

brokencase
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Re: Scorpio Speed sensor question

Post by brokencase » Sun Oct 22, 2017 7:37 pm

I constructed the circuit in perfboard with "point to point" soldering. As you can see it is really not too complicated.
The aluminium is actually the 1 inch square tubing that will be the enclosure.

Below is the potted case. You have to seal the bottom side and then pour the epoxy in.
circuitbefore.jpg
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Attachments
pottedcircuit.jpg
pottedcircuit.jpg (61.55 KiB) Viewed 217 times
Last edited by brokencase on Sun Oct 22, 2017 10:00 pm, edited 1 time in total.

brokencase
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Re: Scorpio Speed sensor question

Post by brokencase » Sun Oct 22, 2017 7:52 pm

There were some mechanical mods required. For better access I reversed the orientation of the gold colored "bracket" on the Vss sensor and so the connector plug would be better situated. This is easy to achieve with some work on the vise. Pry it open and then squeeze it back shut. The bolt securing the Vss was shortened by about 5/8" since the new bracket is lower to the surface of the transmission compared to the original.

These aftermarket sensors have provision for a speedo cable to be inserted. You can get them with this feature or without. Mine came with this but I plugged the hole with a piece of plastic from the junk box and some permatex plastic epoxy - to keep the gremlins out. My plug had a little tab on it, but when I saw how tight everything was under the car I trimmed that tab off.

I then zip tied the circuit housing to the transmission cross member. I just snipped the wires from the old sensor and soldered my module in. Did'nt even fuss with the old sensors connector, just left it in place.

For reference, the original wires for the Vss are:
Black = 12v
Brown = ground
Yellow = signal out.
transmounting.jpg
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Last edited by brokencase on Mon Oct 30, 2017 7:30 pm, edited 1 time in total.

brokencase
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Re: Scorpio Speed sensor question

Post by brokencase » Sun Oct 22, 2017 9:36 pm

Below you can see my view as I soldered it in.

I was expecting a lot of oil spilling out of the hole when I pulled the old sensor out. Nothing spilled out. Is that right?

Another issue. I drove for about a week without the old sensor working. Naturally the fuel computer got really confused. After I put in the new sensor the MPG started working as expected, but the computer still thinks I am close to empty, despite the fact that I went out and topped off the fuel tonight.

Is there a reset procedure with regard to tank fill for the computer? Or does it somehow learn over time?

Have I put this Vss issue to bed? Permanently? I hope so. It all comes down to the reliability of the circuit.
Only time will tell. But the reluctor based sensor should last a long time.

Yes the circuit was a bit of work but this kind of stuff is second nature to me. If someone out there needs this solution but is without electronics skills they can try to find a local electronics hobbyist or ham radio operator and perhaps they can help. I've tried my best to make all the info available so that another can reproduce.
solderitin.jpg
solderitin.jpg (307.08 KiB) Viewed 213 times

Ed Lijewski
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Re: Scorpio Speed sensor question

Post by Ed Lijewski » Mon Oct 23, 2017 7:25 am

Trans fluid won't spill out when VSS is removed (few drops...).

The trip computer C button clears mileage and miles remaining IIRC but the latter should rise to ~ 300 miles +/- on a tank fill-up after ignition key is On without doing anything. (Don't recall.anyone reporting an issue of that sort...) Maybe your modded VSS isn't communicating with the in tank level sensor.

Is that an Austin Healy Sprite in the background?

YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!

brokencase
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Re: Scorpio Speed sensor question

Post by brokencase » Mon Oct 23, 2017 8:57 am

It looks like the computer needs to re-learn the MPG for a bit before it can determine when the tanks goes empty.
With the broken sensor the MPG went close to zero so any amount of gas in the tank is not enough.

Yes, that is a 59' sprite.

Ed Lijewski
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Re: Scorpio Speed sensor question

Post by Ed Lijewski » Mon Oct 23, 2017 10:12 am

I owned a Sprite--so long ago can't be sure of the model year ('58 I think). Not the best car for winter driving in Minnesota commuting to school and work but I loved it in concept and in good weather (heater not up to that winter climate either).. Was squashed in it after slowing to a stop at an intersection with a stopped car in front and a careless driver behind me who didn't brake in a timely manner.

YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!

Ed Lijewski
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Re: Scorpio Speed sensor question

Post by Ed Lijewski » Mon Oct 23, 2017 12:00 pm

I'd disconnect and reconnect the battery to see if the trip meter registers correctly then.

YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!

brokencase
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Re: Scorpio Speed sensor question

Post by brokencase » Mon Oct 23, 2017 8:25 pm

No, the fuel computer is OK now. Drove it to work today and the miles to empty has properly updated and the alarm is gone.
It just needed to accrue some Vss pulses.

I put new rear shocks on it yesterday as well (did the front struts, control arms, and bushings the previous weekend).
Big improvement. Old struts and shocks had no gas in them, original Ford units. And those poly control arm and roll bar bushings were worth every penny. The original LCA to rollbar bushings were torn and perished.

One thing I notice with the polyurethane bushings - the front tires squeal a little on tighter turns. Maybe they will break in.

So I am now back to 100% Scorpio bliss, for a little while at least.

BTW, I went through the car's extensive receipt history. There are three receipts regarding the vehicle speed sensor.
However they all seem to be associated with one event...

1st is dated 2-14-2003 "Auto Electric Specialties" - States "Troubleshoot speedometer & tachometer - found vehicle speed sensor to be faulty and tach to be faulty. No parts available. (obsolete)" $39.60

2nd is dated 2-18-2003 Thomason Ford in Beaverton - E8RY-9E731-B - $97.47

3rd is dated 2-25-2003 "Portland Speedometer" Stated "Labor to install Sensor" $25.00

It looks like the PO went to the first guy, and he was the one to install that test wire I had mentioned previously. But he did nothing else. The PO then did a little research on his own and found out the Vss was available. He got real lucky to find one at a dealer - even in 2003.
Not trusting the first guy and not wanting to pay the dealer labor rates - he then went to the final guy to have the sensor installed!

So the VSS failed for the original owner and its replacement failed for me.

I'm willing to bet it's not going to be a problem anymore...

When I purchased the car in late 2015 the tach was still not working. But as we all know that is an easy fix... and I even calibrated it.

One more thing..i mentioned the circuit was borrowed from an MSD project from the "Silicon Chip" magazine.
That MSD project is in the Bugeye! It's been in there since 2008. I cannot give it enough praise. It is a better than any MSD ignition than you can buy commercially. I am seriously thinking about building another to put in the Scorpio.

Here is a link to the original article in pdf format. http://www.molla.org/DIY-CDI/SC-DIY-CDI ... -hires.pdf
Last edited by brokencase on Mon Oct 30, 2017 7:34 pm, edited 1 time in total.

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