Moe

a 968 with the hall sender unplugged?

I just want to see how it runs disconnected, I'm waiting on a new hall sender.

7thStranger

When my wire broke on mine I was driving it.

It was real hard to start and had no power.
The DME will cut back the timing if it does not get a reading.

It took me about 6 months to track down that litter bugger.

Tom Carson

shouldn't effect very much...cheap low octane gas and you will experiance detonation which can at some point do damage

pca.org had some good stuff regarding this including a Q & A about the 968 sensors

Q:

The dealer told me the hall unit in the ignition is not functioning and the car is running on a flywheel ignition trigger. Apparently, the hall unit is not in the distributor. Where is it located and is it easy to replace?

A:

The hall unit is a sensor much like the speed and reference mark sensor that provides information to the DME unit so it can make ignition and fuel injection decisions. In the case of the speed and reference mark sensor, it is a simple magnet wrapped with a coil of wire that induces a very low voltage every time a tooth on the ring gear passes by the end of the sensor. As the tooth moves and a gap appears, it generates current in the opposite direction. On an oscilloscope, the voltage looks like a sine wave. A couple of missing teeth on the ring gear is interpreted by the control unit as the reference point. Earlier 944 models used two sensors, one for engine speed and a separate one for the reference point, but 968's use a common sensor for both.

From an engineering point of view, the DME will know by was of the reference point where the flywheel is in relation to top dead center. What it can't know is which cylinder is at the top of its compression stroke, cylinder 1 or cylinder 4. The hall sensor picks up a signal from the back of the camshaft (which rotates at half the speed of the crank,) and tells the DME when cylinder 1 is at the top of it's compression stroke.

This is only required for the DME's knock sensing system, which is capable of retarding the ignition timing to individual cylinders. So the dealer's advice to you makes perfect sense: your car will run without a functional hall sensor, but the built-in knock sensing system will be disabled.

The hall sensor itself is quite easy to find because there's a wiring harness and connector leading from it. Start your search in the area behind the distributor housing on the cylinder head. Ease of replacement depends upon your level of technical expertise, but on a scale of 1 to 5 with 5 being toughest, I'd give it a 2.



Bill Burris - PCA WebSite - 5/17/2003

Moe

Went to the garage this morning, and with the Hall Sender disconnected, she "hard started", slow revved, and ran exactly the same as it did with the Hall Sender connected. Didn't let it run for long, I was so relieved that none of the problems changed. I guess the Hall Sender has been "bad" for awhile. It started running funny before I parked it last year.

Thanks to all replies, I'll have more questions when the part gets here. :-)

I did notice improvement (in idle speed) when I replaced the TPS earlier this week, that was before the Hall Sensor plug went south. Seems they (TPS and Hall Sender) must work together.

Thanks