RB25 S2 Ignition help (Tach wire question)

[jacksonbrown]

I have traced the yellow/lavender wire from ECU to behind intake and it ends with plug below. Two different ECU's , factory or aftermarket tach, continuity from ECU pin to this connector OK, still no tach signal. I also was wondering if the second plug here has anything to do with it? Cant find any info on what was plugged in here (was told ignition?) Also wondering if S2 is supposed to have resistor in igniton wiring? THANKS for any info. [IMG][/IMG]

[IMG][/IMG]

[jacksonbrown]

Anybody have a clue?

[Darius]

Look up a pinout of the ECU plug in the FSM. It says what each wire is for. I believe the tach signal wire is pin 7 and it Y/?. Could be blue striped?? Wait, do you think "L" on the coloring code means "lavender"? It means blue. Might want to recheck that. You must be tracing the wrong wire because the tach signal wire is an output from the ECU directly to the gauge cluster.

Let me know if that helps or not.

[jacksonbrown]

Yes I have the right wire and have tugged on it with engine running, two different tachs, different ECU, still no signal at the ECU pin or under the hood. Wondering where else I can get a tach signal from ? THANKS AGAIN

[Darius]

Alright I looked into this a little further. The first pic with the small single Y/L wire ending at the plug with the cap on the end is the "tach output test plug". That wire is tee'd off between that test plug and the ECU with another Y/L wire that runs to the M63 plug for the dash harness ==>gauge cluster. If that Y/L wire is not pinned correctly in the dash harness (and I don't know what chassis you are working with), no tach signal is going to make it to the gauge cluster.

The second pic you show is definitely not part of the tach wiring. I actually think I remember that L/R wire being part of the wiper wiring. It has been a long time since I figured that out though.

Have you tried to get a tach signal right at the ECU pin #7? Any kind of a 0-5V signal?

[jacksonbrown]

I spliced into the wire about 4 inches out of the ECU (where it tee's, one going under hood to plug shown, other going to dash tach) hooked in after- market tach and still nothing. I dont know exactly where the ECU gets its tach signal output from but that must be the prob. I have continuity from wire under hood all the way to ECU pin and ran new wire from pin to new tach.I've got some of rb25 schematics that are on the net, but they are not detailed enough. I have also noticed differences since mine is a series 2. Thanks Again, I will hook a meter straight to the tach output pin on ECU and see if I have anything.

[Darius]

the ecu takes the signal from the cas and converts it into a voltage that it sends to the cluster.