XR LA2/3 Install. VSS Sensor Question

[justpushplay]

Hi All,

I'm getting ready to test fire my LA2/Big VAM install, and the only thing left on the list is to install the speedometer mounted (I think) VSS sensor. Reasons: My understanding is the LA2/3 will shut the pusher (condenser) and puller (radiator) fans off above 40-45 mph. I like this idea, quieter, less current draw, fewer hours on the fans. And possibly better cooling with the fans off at speed. (maybe?)

This is the VSS I have, is this the correct one for the XR speedometer? Is there a short section (inches) of speedometer cable missing for this sensor?
I've already pinned the harness and run shielded microphone cable to the speedometer location. Does this unit simply plug into the XR speedometer, and then the speedo cable plugs into this, or do I need a 2 piece speedometer cable? (I think my other XR, an auto trans car has a 2 piece cable. It also has cruise) Should I just quietly walk away and never speak of this again? You would think that after having two Xr's in the garage for 36+ years, I would just instinctually know this stuff!

[andyofcolumbusmerkur]

To me it looks really similar but not exactly like the stock VSS on cars that came with cruise and the 2 piece speedo cable.

[justpushplay]

I found this one on eBay for $13:-) It may not even be applicable to the Merkur LA2 mod. I'll have to pull the speedo assembly loose on my red '88 auto, and see what is going on there. It has cruise, but the cruise stuff is mounted on the driver's side wheel well. My understanding is the VSS isn't part of the cruise system, but maybe the auto speedo cable will allow the VSS. In other news, I did the first test drive, and the rest of the LA2 install works perfectly, so there's that. It's everything people say it is. The car sounded different just firing up. Idle is so much smoother. WHY did I wait so long to do this swap? I've had all of the pieces since around 2018.

[justpushplay]

Here's another one:

Ford Vehicle Speed Sensor E4ZZ-9E731-A Mustang 83-89 Thunderbird 84-88.jpg (210.28 KiB) Viewed 3559 times

Ford Vehicle Speed Sensor E4ZZ-9E731-A Mustang 83-89 Thunderbird 84-88

I'll get to my '88 today and see what-if it has behind the speedo

[andyofcolumbusmerkur]

That looks more like the one I removed from my 89. The upper half of the 2 piece cable is maybe 18 inches long, and the plug from that VSS goes into the cruise control stuff in the engine compartment. Then the long section of cable goes into the transmission. Mine was bad down at the transmission probably because it (cable) didn't have enough lubrication.

[my8950]

Hi All,

I'm getting ready to test fire my LA2/Big VAM install, and the only thing left on the list is to install the speedometer mounted (I think) VSS sensor. Reasons: My understanding is the LA2/3 will shut the pusher (condenser) and puller (radiator) fans off above 40-45 mph. I like this idea, quieter, less current draw, fewer hours on the fans. And possibly better cooling with the fans off at speed. (maybe?)

This is the VSS I have, is this the correct one for the XR speedometer? Is there a short section (inches) of speedometer cable missing for this sensor?
I've already pinned the harness and run shielded microphone cable to the speedometer location. Does this unit simply plug into the XR speedometer, and then the speedo cable plugs into this, or do I need a 2 piece speedometer cable? (I think my other XR, an auto trans car has a 2 piece cable. It also has cruise) Should I just quietly walk away and never speak of this again? You would think that after having two Xr's in the garage for 36+ years, I would just instinctually know this stuff!

It goes in series with the speedo cable. Just make sure when you plug it together, the square drive cable is in the correct position, otherwise you make that straight cable and funky...I am not sure of the fans shutting off with this, my fans rarely come on, unless manually controlled on by the A/C switch. That was the case with the PK1, PF3, and now an LA3 EEC...

[Ed Lijewski]

Should I just quietly walk away and never speak of this again?

Probably.

The Turbo Coupe VSS is a different species than the Merkur XR4Ti VSS.

The Turbo Coupe and Merkur Scorpio VSSs drive speedo, odo, and cruise control. The XR4Ti only drive cruise control.

At the least you'd need to confirm the XR VSS signal is the same form as the LA2/3 needs to see for controlling the fans.

But note too that beyond a correct VSS signal you'd need to add wiring (and maybe separate relays) to the XR harness for the fans. Studying the Turbo Coupe wiring diagram would be instructive..

YMMV

[DPDISXR4Ti]

Should I just quietly walk away and never speak of this again?

Probably.

The Turbo Coupe VSS is a different species than the Merkur XR4Ti VSS.

The Turbo Coupe and Merkur Scorpio VSSs drive speedo, odo, and cruise control. The XR4Ti only drive cruise control.

At the least you'd need to confirm the XR VSS signal is the same form as the LA2/3 needs to see for controlling the fans.

But note too that beyond a correct VSS signal you'd need to add wiring (and maybe separate relays) to the XR harness for the fans. Studying the Turbo Coupe wiring diagram would be instructive..

YMMV

I don't often agree with Ed, but in this case I will. As Ed Suggests, go take a look at the TC schematic. There is a lot going on to support the cooling fan strategy on those cars. It's not at all as simple as just hooking up the VSS. And OBTW, the VSS signal is not the same between the two cars.

Wow, I agreed with Ed twice in one post! Write this date down - it will never occur again!

[justpushplay]

I'm hoping I just need to keep the LA2 happy with whatever VSS signal it was fed in it's previous life. Off to find the schematic for the TC. This isn't a must-have for the car's functionality. After a couple rounds of TPS, timing, and idle adjustments, I really like the behavioral changes the LA2 brings. The only code is an 82, relating to the the missing IRCM module. And a simple jumper has solved the angry WOT green relay issue. I just like the idea of not running the engine cooling fans non-stop with the A/C on. Let the computer manage those as if the A/C wasn't running. If anything, using A/C at in-town traffic speeds, I would rather the condenser fan run. I should probably focus my attention on getting the ported E6, new turbo, 3" DP and 3" cat/muffler/resonator to the bumper exhaust installed. (although the 220k miles original turbo works fine) The new exhaust should make an even bigger difference, I suspect my cat is partially clogged. At 5k/15 lbs. of boost, the stock exhaust sounds like my shop compressor air nozzle blowing out a computer.

BTW, is everybody sticking with 10* of initial advance? I am quite fond of my factory original head gasket, but wondering if a couple of additional degrees would improve low RPM throttle response even more than the LA2 has.

[andyofcolumbusmerkur]

I had my cars base timing at 13 because I read that in the factory service manual. Then I learned the PE (Mustang SVO) computer wanted 10 degrees. The car felt way more tame at that base timing. Playing around with it I liked about 14.5, but it made it start a little more difficult. Like an old carbureted vehicle in need of a tune-up. So I may leave it in the 12 to 14 range depending. The stinger webpage says not to try and advance the timing for more horsepower because the computer is smarter than you may think. This may be the case sometimes. I don't have the knock sensor hooked up, and fresh 93-94 octane gas is used. I never felt any detonation playing with the timing but did when playing with the boost. So I let off the gas as soon as I felt it. Will you blow up your engine advancing the timing? Maybe. Will you blow up your engine playing with the manual boost controller? Maybe. To quote ED your mileage may vary.

[DPDISXR4Ti]

I'm hoping I just need to keep the LA2 happy with whatever VSS signal it was fed in it's previous life.

You don't need the VSS input. I suspect most swaps have been done without it.

[Jack_James]

Base timing on MTX cars is 13°. ATX cars are 10°

[my8950]

I'm hoping I just need to keep the LA2 happy with whatever VSS signal it was fed in it's previous life.

You don't need the VSS input. I suspect most swaps have been done without it.

This is true, I did not wire the VSS to the EEC when I did LA3 swap, not that I am the only one who has done this.

[justpushplay]

I have now entered the world of PPM, (pulses per mile, 8k seems to be a sort of standard) square wave, leading edge, trailing edge, etc. (I've been through THAT already with SMPTE time code in my real job) I took that larger sensor that I have in the above pics, and driving it with a drill, can generate 7 volts AC, and 8 pulses per revolution.

https://www.dakotadigital.com/index.cfm ... /prd57.htm

https://www.dakotadigital.com/pdf/SEN-01-4280.pdf

https://www.dakotadigital.com/index.cfm ... prd109.htm

Rock Auto has this listed for my '88 C3 Auto:

https://www.rockauto.com/en/moreinfo.php?pk=3842949

Which looks like the one I already have. I'm counting 8 'pulses' per revolution. Will that make the LA2-3 happy? What's the pulse rate of the T5 mounted VSS? Is this the hint that I need to put the T-5WC I have had for years in the white XR?

And now for an incomplete update that really add's nothing but more questions: Here's my Red '88 auto's VSS:

[justpushplay]

I have now entered the world of PPM, (pulses per mile, 8k seems to be a sort of standard) square wave, leading edge, trailing edge, etc. (I've been through THAT already with SMPTE time code in my real job) I took that larger sensor that I have in the above pics, and driving it with a drill, can generate 7 volts AC, and 8 pulses per revolution.

https://www.dakotadigital.com/index.cfm ... /prd57.htm

https://www.dakotadigital.com/pdf/SEN-01-4280.pdf

https://www.dakotadigital.com/index.cfm ... prd109.htm

Rock Auto has this listed for my '88 C3 Auto:

https://www.rockauto.com/en/moreinfo.php?pk=3842949

Which looks like the one I already have. I'm counting 8 'pulses' per revolution. Will that make the LA2-3 happy? What's the pulse rate of the T5 mounted VSS? Is this the hint that I need to put the T-5WC I have had for years in the white XR?

And now for an incomplete update that really add's nothing but more questions: Here's my Red '88 auto's VSS:

Here is my eBay VSS plugged into the red XR's speedo cluster.