PeachParts Mercedes-Benz Forum - View Single Post - Piggyback ECU installation write-up

Blown_M104 · #3 11-01-2005, 10:05 AM

Best of luck with your Apexi install, I think you'll be very pleased with the results. Below is a summary of the wiring connection points.

For the MAFS I spliced into the 4-conductor cable going to the MAFS from the ECU. The yellow wire with white strip is the output signal.

For the RPM signal I tied into the Cam position sensor wire in the wire duct on top the fuel rail. This is a shielded cable with a pink center conductor. Just connect to the pink wire.

For the throttle position signal I went directly to the cable connector at the throttle body. The Factory wiring diagram list the actual-position-sensor wire as being red/yellow for my model. The wiring diagram is wrong! Red/yellow is for the set point potentiometer; the red/white wire is the actual position sensor which is what you want.

+12V power I got off pin 7 on the over-voltage relay. You might have different style relay, just find a pin that is switched with the key position II.

The Apexi has two ground wires, follow the instructions that come with the unit for connecting them to the ground wire going to the ECU (solid brown).

I ran the wiring harness for the piggyback though the pass side firewall and then mounted unit under the dash. I high recommend soldering all wire splice connections and using wire rated for engine bay temperatures.

Math:
I’ll email you two spreadsheets I used; one is for injector sizing and the other calculates increased airflow (as weight) at different levels of boost and for two different desired A/F ratios. The air density calculations are all based on equations I got from this very cool link :

http://webpages.charter.net/chrisstephens/EEC%20Help%20files/Files/Air-Fuel%20Flow%20Calculators.htm