Generating a tach signal to drive stock tach?

[Cougar281]

I currently have some sort of 3rd party module, don't recall who made it but it's somewhat similar to Autometers 9117 module, but not quite as it didn't involve cutting the coil power supply wire. It worked fine for quite some time, but these days, sometimes it works, other times it pins the tach at about 2200 after startup.

I ordered a Dakota Digital SGI-100BT with the idea being it would drive the stock tach and also drive the speedometer off the PCMs VSS output that is generated off the OSS signal all in one module. The SGI-100BT does drive the speedometer off the PCMs VSS output as expected (just disconnecting the VSS Sensor and tying the vss out on the PCM didn't work, I think because the VSS out on the PCM is a square wave and the VSS sensor is an AC sinewave - I think it fried the original speeometer, because it didn't work afterwards and I replaced it, but the cruise control module seemed to 'understand' the PCMs output), but the tach just jumps like a Jack Russel Terrier. Dakota Digital basically said I need to get another module to smooth out the input signal, at which point, we're talking about just replacing the module that's flaking out.

I'm not really keen on Autometers unit as it requires cutting the coil power and running all power through their module. If memory serves, the one I have is connected to either one of the coil trigger wires or the crank sensor wires. I'd have to dig it out of the car to see what it is and how it's wired, but I believe this particular unit is no longer made.

That all being said, does anyone have a suggestion for a clean way to drive the stock tach, considering the PCM I'm running (PTP2/FBFG2 moved to FBGI0 strategy) lacks the ability to output a tach signal?

[decipha]

yeah just swap in a 99-04 gauge cluster

its only 2 wires from the ecu to the cluster

the ecu does not have a vss out nor a vss

[Cougar281]

The problem with the cluster swap is I'm not aware of any cluster that uses data that would fit in a Cougars dash, let alone look proper.

The Mustang PCM does have a VSS out signal - Pin 68. That goes to the speed control servo and if the car has the Mach 1000 or Mach 460 sound system, the radio as well.

[decipha]

ah yes my mistake, I thought you were specifically referring to the cluster input.

the cougar and the mustang cluster isnt similar enough in size to make it fit?

if need be swap the mustang dash

I tuned an ls swapped foxbody where the guy fabbed up an ls1 cluster in a stock fox dash. Im sure you can fab something up.

[Cougar281]

The goal is to keep it stock-ish. The problem is the only other clusters that I know of that fit in the space properly-ish are late 90's Taurus clusters. But they operate the same way the Cougar cluster does, driven off the VSS sensor on the transmission and PCM for the tach.

I dug into the car and the device I have now is a 'Tach Adapt' by Pony Express Performance, but best I can tell, they closed their doors a long time ago and no one else makes an adapter like this one (It uses the crank sensor signal to generate the tach signal).

Eventually, if time and money ever allow, I want to do a full restore on the car, so a major dash swap isn't an option, plus I can't see how some other dash would fit in the car.

I guess maybe another option would be to switch to a Marauder PCM. Most of the pins between the Mustang and Marauder PCM are the same, with a relative handful of differences, some of which simply don't exist on the Mustang PCM, and it has the tach output. Only problem could be the fans, as it doesn't look lime the Marauder PCM has the ability to control simple high/low fans, but instead some sort of PWM fan.

I'll have to keep searching and see if I can find something suitable.

[decipha]

if all you want is tach why not just simply add the tach output to your pcm

fyi marauder ecu had tons of outputs, u can control pwm fan and low+hi if you want

pin out between marauder and mustang is the same

[Cougar281]

How would I add a tach output? The pin used for tach output on every other PCM (48 I believe) has no output (I originally left the pin in place and the tach didn't even twitch). I seem to recall reading that the PCM doesn't have the hardware to do it, like how PCMs that were stock manual trans PCMs don't have what's needed to control an auto trans, while an auto trans PCM you can just turn the trans functions off if you want to run a manual trans. If there's a way to actually enable it in the PCM, I'm all ears.

As far as the 2004 Marauder vs Mustang PCMs and pinouts, on paper at least, a lot of pins are the same, but some are different in one way or another - 2, 7, 8, 9, 10, 12, 17, 18, 19, 20, 24, 28, 30, 31, 38, 42, 43, 44, 45, 46 48, 66 (sort of), 70, 77 & 82 are the ones that I found, on paper, to not match. Now, some, like pin 2, which is the MIL control, I THINK, without digging into my harness, actually does work properly, despite not being used according to SI, same with the OD lockout indicator (pin 12). But as I recall, pin 48 is dead. And others on the Marauder PCM are used for something but listed as not used for the Mustang PCM.

I'm also game for trying to acquire a Marauder PCM and connect it as long as doing so isn't going to fry anything But assuming it won't fry anything (My concern with frying something are with the pins that are different - some of which I believe have no connection in my harness, but any that do..), I'm sure it won't run well since it has a DOHC calibration and I still have the SOHC in the car.