Porsche Repair: 1987 Porsche 944 Died, No Spark, crankshaft position sensor, air flow sensor

Question
I was driving home last Thursday and my 1987 Porsche 944 just quit running.  My first thought was "Oh, no.  Timing belt gone, again!"  The car got towed to the garage and timing belt is ok.  There is no spark to the engine, however.  It turns over, but will not start.  

Now the mechanic is not a Porsche-certified mechanic, but he's pretty savvy.  He's gone through and made sure all ground wires are tight.  After many tests, he thinks, maybe, possibly, it could be the crankshaft sensors.  Reading some of your other advice, it looks to me like it would more likely be the air flow sensor.  Help?!  Also, does the clutch have to be pushed in for the 944 to start?

Thanks.


Answer
Hi B.J.,

First, this is the only time anyone's asked about the clutch.  I don't see anything on the wiring diagrm for the '85 model (newest I have) that suggests the clutch needs to be depressed.  I suppose it could be an '87 "enhancement", but I really can't say.

Without a spark, the airflow sensor is not in play, so it should be thought of when there is a spark, but no start.  So...just moments ago I responded to another writer about the crankshaft position sensor, saying in part:

"This is a bit obscure, but your car's computer needs a signal from the
reference mark sensor telling the computer how many times the
crankshaft is revolving, and this is critical during the engine cranking phase and the initial start phase.  It's clear from the wirng diagram the
sensor has a black plus a yellow wire leading to the computer but I don't
know exactly where it's located.  Intuitively, it would be pointed at
the crankshaft at the damper with all the timing marks on it. If you can
find it, you should be able to test it by watching for voltage while
cranking.  If there's none, that's the problem...or...there's also a
possibility the sensor could be there but mal-adjusted."

As I suggest, the crankshaft sensor issue is a bit obscure...and something tells me here again...that without a spark, the sensor isn't in play yet.  So..

What else?  Does the ignition switch send voltage to the coil at "run" and "start"?  I'd start with those even more basic questions.

Dave