Vehicle: 1988/ Porsche / 944 Turbo S
Engine: 2.5L, I4
Injection: Megasquirt-II V3. code 2.35 controlling fuel only, 55 lb injectors, mostly stock wiring harness.
Description of what I did:
1.Throttle position sensor (TPS) Pin 22 tap and supply pin 21, works perfectly with Megasquirt.
2. Coolant temp works: DME Pin 13 to megasquirt. The resistance needs to be adjusted accordingly in Megatune.
3. Intake air temperature sensor (IAT) is connected to the port previously used by the stock idle control valve. The open line to this has a little air filter connected. It would be better to have a new port welded, but I'm having trouble finding someone who will weld aluminum. Wires will need to be routed under the intake manifold to the passenger footwell.
4. I'm using a PLX m300 wideband that works flawlesly with the MS.
5. Triggering is done with pin21 from the dme (tach signal). I found that the MS draws too much of the signal and doesn't allow the DME/KLR any signal left to process the rest of the ignition. There was no tach jumping on the dash and no spark to the coil. The solution was to put a 1.2k ohm 1/4 watt resistor in the line to the megasquirt. With the resistor in place, both devices have functioning tachs.
6. I decided for simplicity sake to reuse my ballast resistors and set the MS accordingly with my low impedance 55lbhr injectors. I'm using spade connectors in case I want to switch them out in the future. MS calculated a nice VE table for my setup and it's running well untuned and just a little rich now. The next step is retuning for a more exact fuel table.
7. The DME needs a load signal, which is usually derived from the air flow meter (AFM), to calculate spark advance. I guess any type of MAF or AFM would do the trick as long as it output a 0-5V signal. This signal goes to Air flow sensor Pin 9 on the DME. I'm reusing my old guru racing Link AFM to generate a load signal. Hopefully someone smarter than me can figure out a way to get around the need for this. The MS can also use a MAF signal to generate the fueling characteristics, so you could plug in a generic MAF and be off and running.
That is how I got my car running with it, I do not make any claims that this will work for everyone. YMMV!
Again, Big thanks to AlexE (ae1969) for his expertise and the laptop he generously loaned me.