Yeah, I'm starting to think that maybe there is a bad connection at the speed sensor because the tach seems to work intermittently. I'm going to go hook the scope straight to the sensor output and check to see if it is functioning.

 

Okay, new update.

I disconnected the wiring harness plug at the engine speed/position sensor and hooked the sender right to the oscilloscope. I cranked the engine and got a sine wave. So, I reconnected the harness (bloody difficult, too) and went to test the terminals on the EZK plug of the harness, as per the repair manuals. I got no sine wave whatsoever.

Is there some problem which might cause that interruption between the speed sender and the plug (such as the hall effect sender), or am I gonna have to pull the whole thing out and ship it back to 928 intl as a dead harness?

Thanks again for everyone's help!

I should point out that I built my own oscilloscope using my computer's soundcard, some shareware I found online, and a microphone jack with test leads and a voltage divider wired into it. It ain't pretty, but it clearly works. The only downside is that I can't control the scale of the time axis on the scope, so it's difficult to tell whether my readings look like the ones in the manual. However, I figure that if I get ANY sine wave whatsoever that I should find the same sine wave on the other side of the harness. This may be a flawed assumption, as I don't know much about how the circuitry is designed/wired, but IIRC the wiring diagram just shows a straight input from the speed sender to the EZK unit, in which case I WOULD expect the same waveform.

 

Did you check at pin 23 of the EZK ? However, if you get some action at the tach, this suggests the EZK isw getting an inpuit signal from the sensor. The tach is driven from the rpm output of the EZK (also drives pin 1 of the LH to "wake" it up.

Have you checked for spark ?

 

Checked for spark repeatedly, got nothin'

Also, I may be calling shennanigans on that tachometer-sender thing. I had the sender hooked up directly to the oscilloscope, so it was NOT connected to the harness, and when I cranked the engine, the tach responded. That makes no sense to me, but it is what it is. I'll see if I can figure out how that is happening, and hopefully it isn't a result of my own stupidity.

 

OK, I couldn't see anywhere that you had checked for spark.

I would check the grounds very carefully, especially the one that sits partly under the throttle cable pulley.