speed dial or just use vss signal off the tranny?

[48prerunner]

Anybody skip the speed dial and just wire the vss signal straight from the trans?

[48prerunner]

Ok so 8urzo6 over on the modular ford forums helped me out and then I did alittle more re-research to refresh my mind on why I needed the speed dial with my t-45






http://forums.corral.net/forums/gt-s...ps-suck-4.html

post #125 I just copied and pasted it here if thats ok? if not mods can delete it.
I figured I'd add a little value to this thread, and make a little clarification here.

94-98 cars have a VSS (Vehicle Speed Sensor) system where the VSS sensor is expected to generate an 8000 pulse per mile signal. That signal goes to the PCM, the speedometer and the cruise control system.

99 and up cars use an OSS (Output Shaft Sensor) system which tells the PCM only at what speed the output shaft is turning. The PCM then uses values in the tune for Tire Revs/Mile, axle ratio and OSS sensor tooth count to calculate the speed. The speed information is then sent as digital data via the CAN bus to the instrument cluster. The instrument cluster microcontroller then points the speedometer needle to the correct speed. OSS sensor systems run somewhere around 32000 pulses per mile (depending on tire size and axle ratio), about 4X the frequency of a VSS system.

The variables you need to consider are: what kind of speed sensor does your transmission have, what does your PCM expect and what does your speedometer expect. (I have no idea how the cruise control systems work.)

If you are doing a Coyote swap, your PCM is expecting an OSS signal. If you give it a VSS signal, the PCM will think that the car is going about 1/4 the speed it really is going. So if the PCM dashpot threshold is about 5 MPH, and it is getting a VSS signal instead of an OSS signal, the actual dashpot threshold will be about 20 MPH.

If you have a VSS transmission and a VSS speedometer, you should leave the VSS signal connected to the speedometer, stock PCM and cruise control. But you will need to splice in the input for the FRPP Recalibrator unit to the VSS signal. The output of the FRPP recalibrator with the speed signal scaled up should be connected to the Coyote PCM OSS input.

I am not sure why FRPP tells you to set the switches to 1,1,1, but it seems to work.

I ran a test on my bench tonight where I set up a Dallas Mustang Speedcal to see if it could do the same thing. I suspected that it would not work because the DM Speedcal puts a 6V DC bias on the VSS sensor signal when you put it into the circuit. And I was correct. The VSS speedometer does not work if you connect it to the VSS sensor in front of the DM Speedcal.

If you are running an OSS transmission with a 94-98 speedometer, you would run the OSS signal to the Coyote PCM, and then run the FRPP Recalibrator output to the speedometer. I am assuming the FRPP Recalibrator has enough range to make the speedometer accurate, but have not tried it so caveat emptor.

If you are swapping a Coyote motor into a 99+ car, I have no idea how to get the 99+ instrument cluster to work with the Coyote PCM.

HTH
Mark Olson
96 Kenne Bell Cobra: See http://www.classictiger.com/mustang/ for mods.

[edwardb]

Anybody skip the speed dial and just wire the vss signal straight from the trans?

I am far from an expert on this subject. Understatement of the day. But I'm trying to learn since I'm doing a Coyote in my current build. To be honest, there are a number of different factors, and now maybe complicated by two versions of the base Coyote control pack. One for the 2011-2014 version, and a new one for the 2015-2016 Coyote. I'm doing the newer one. Pretty random statements:

- The forum notes are interesting, but much of the info is to get older speedos to work with the different speed sensor signals. At least for Speedhut (which I've used) it will calibrate to either the VSS or OSS. I've done both on previous builds and works fine.

- Neither of the control packs support either cruise control or automatic transmissions. So the crate Coyote doesn't "need" a speed signal for either of these purposes.

- Many of the newer speedos don't need a speed signal either because they're GPS based. My situation as well.

- The reason for the speed dial add to the 2011-2014 control pack was to address a driveability/stalling issue. Really nothing to do with speed itself, apparently, but just some kind of indication the vehicle was in motion or not.

- The earlier versions of the 2011-2014 control pack did not support the speed dial directly. It was necessary to break into the harness and tap into certain leads. Later versions are listed as having the speed dial wires directly available.

- Supposedly it was possible to program out the need for the speed dial in the 2011-2014 control pack. I've seen several references to builds using custom tunes where the speed dial was not used or needed.

- The instructions for the new 2014-2015 control pack make no reference to the speed dial. I questioned Ford Racing about this, and the tech said he "thought" the new control pack doesn't need it. But he admitted he wasn't 100% sure. His recommendation was to install the engine and control pack and only add later if needed. That's what I'm planning to do, but to be honest I'm a little nervous about it and not too happy about the possibility of having to break into the wiring after the build is done.

- I'm installing a TKO600 which does have the OSS signal available, even though I don't need it for the speedo. But it would be available to go direct to the PCM if that's necessary and/or supported.

In summary, the answer to the question of whether the VSS can be directly connected to the PCM? Sounds like no. But it does sound like the OSS could be. But, at least in my mind, the requirement is not clear. Sorry in advance if my comments are too random or aren't correct. Like I said, still learning.

[48prerunner]

I ended up using the speed dial to fix my stall issue