kccampro

I need a hand from someone with a running S4, I don't think it matters which trans. I'm trying to get an idea what the voltage signal looks like from CE panel connector J11 to the tach (EZK to the tach). I'm running a non-Porsche ignition with my mega squirt and I'd like to figure out how I can retain my factory tach. After tracking down all the connections to the tach on the schematics, it looks like I may be able to feed the tach signal through J11. However, I have don't want to just assume that the tach is getting one 12v signal for each engine rotation. A little background, I'm running an '87 S4 auto cluster. Since my car is a manual, the 'P' on the tach now indicates that my low volume pump is feeding my fuel surge tank and I wired the 'R' to the back up light circuit so that still works as it should, I know, I know... what kind of dumb *** with a manual doesn't know that he is in reverse. The wiring was right in front of me so I did it, don't judge.

Anyway, if anyone wouldn't mind putting a multimeter (or scope?) on J11 and maybe I can figure out what the signal looks like to the tach. Thanks!

FLYVMO

Not sure about the megasquirt, but my Tec3r tach output was a direct hookup to J11, which was black and purple wire?? I think. The ECM sent the correct signal and it knew it was a 8 cylinder in the software.
Hope it was of some help to you

Cheers!
Carl
90GT project

kccampro

In this case I'm actually trying to figure out what the of signal a stock EZK ignition looks like to a factory tach. I'm guessing that it's a 12v signal that may trigger from the negative side of the coil... But it may be more sophisticated than that.

jcorenman

Here's a file-photo of the tach signal (blue trace) and one of the two ignition-drive signals (red). The tach signal is 12v, two pulses per engine rev (i.e. same as a 4-cyl motor, because of the split ignition I presume), rising edge is TDC/BDC. This was at idle speed.

The tack output is pin-13 from the EZK, to LH and then to W11 on the CE (blue/white), departs on J11 (for an '88) for the cluster (0.5mm green wire). Digi-dashes are different, the tach signal arrives from the EZK on W11 as before but departs on M11 for the cluster (also 0.5 green).

kccampro

Ask and you shall receive... Thanks much