Thank you very much for that! I apologize for not checking the thread until now.

I checked the workshop manual http://www.cannell.co.uk/944_workshop_Manual/Vol1A-Engine.pdf and there's a piece about checking the hal sensor on page 135. It says the signal goes from 0 to -5 Volts. Can your determine if that's a weak signal or is it a matter of Amps? I'm not that good with electronics.

Maxcar:

The issue that I see in regards to tapping directly into the Hall Effect device's output signal is one of impedance matching. From what I remember about Hall Effect devices are generally buffered by high impedance Operational Amplifier configured in a differential mode. This is an analog circuit that is detecting milli or micro volts differences (or milli or micro amp current differences). If you shunt a low impedance device (such as a digital RPM input device) around the Hall Effect device’s output, there is a good possibility that the signal will be distorted (e.g. electrical noise).

If you look at the Porsche factory schematic you will notice a shielded wire running from the Hall Effect device to the ECU. This is a strong indication that Porsche wanted to shield a low voltage/current circuit from electrical noise. This is also generally done on high impedance (analog) circuits because of their susceptibility to injection of electrical noise.

The advantage of making the connection described in #3 above, is the analog Hall Effect signal has been buffered and is in essence a relatively low impedance digital signal that would not be effected by you tapping in a RPM digital input device.

Let me know if that makes sense or not.

Dale

Maxcar:

After giving your question a second consideration, you could contact your vendor to ask about the input impedance of their Tach input. If they say that it is a high impedance (megaohms), then you could attempt to connect to the Hall Effect device. Just be aware that you may cause signal degradation to the ECU or the tachometer.

Dale

Ok, now I see the problem. It doesn’t seem like a very good idea to clip onto a shielded wire. I’m having some trouble interpreting the diagram, so if you could help me it would be great. I can’t see the match of the wire colours between the hall sender on page 97-217 A46 and page 97-207 M16. Is it really the same sender?

I’m now more leaning towards using the tachometer signal wire behind the instrument cluster. As far as I can see, it should be the Blue/Red wire on page 97-207 F14, right? What does the 0.5 before BL/RE mean, by the way?

Thanks a lot for the help.

Hi Guys,

We spent a lot of time install an AIM MXL into our 944 and redoing all of our wiring. I tried to put some notes down in detail in our blog since I couldn't find much helpful information in the forums. We spent a lot of time going through the wiring diagrams to get this all working right. AIM Tech support is also a great resource.

www.langracing.com/installing-aim-mxl-pi...-other-motronic-ecu/