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New Distributor because of sensor?

 
Old 12-09-2005, 07:32 PM
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SNOWBIRD
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Default New Distributor because of sensor?

I hate posting really stupid questions... I did a search and couldn't find anything on it in the 964 forum. My 92 C2 is in a well respected shop getting a 60M service done. In the middle of closing a deal on the phone, I got a call today from the shop (so I was only half listening to the guy). He said that a relay or sensor is bad in the distributor that has someting to do with the fuel injection... They are putting in a new (I think) or rebuilt distributor because of it. Says it'll cost around $700 sells for $1200 (List?). I figured not much point in challenging the guy, he has my car and I'm 1200 miles and 3 weeks away from seeing it anyway. I'd just like to be enlightened to what the thing is.
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Old 12-09-2005, 09:53 PM
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Richard Curtis
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The twin distributor, rebuilt with new belt, caps, rotors, etc., from Pelican is $748.50. Sounds lke your mechanic is offering you a deal. I suspect the sensor he's referring to is the Hall Effect sensor.
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Old 12-09-2005, 11:33 PM
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Originally Posted by Richard Curtis
The twin distributor, rebuilt with new belt, caps, rotors, etc., from Pelican is $748.50. Sounds lke your mechanic is offering you a deal. I suspect the sensor he's referring to is the Hall Effect sensor.
Yep, thats what he called it.. Can't get them anymore, without buying the whole distributor, huh?
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Old 12-10-2005, 01:11 AM
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What were the symptoms before you took the car in for service? A Hall effect sensor is a $20 part. Somebody could make some money if they could reverse-engineer a replacement for the one in the 964 distributor.
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Old 12-10-2005, 08:55 AM
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springer... As far as I could tell the car was running fine.
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Old 12-10-2005, 11:20 AM
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My books are all packed away or I would find out what the Hall sensor does. Can anybody explain the purpose for the Hall sensor? The DME uses the crankshaft position sensor to figure out how fast the engine is spinning and where everybody is. The Hall sensor may be redundent to that signal, perhaps for limp home if the crank position sensor fails?
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Old 12-10-2005, 11:49 AM
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In Post #6 of this thread Red Rooster (Geoff) states:

"The Hall sensor in the distributor generates a cylinder reference signal for the DME so that the sequential injection works correctly.The motor will still run if this signal is corrupted or missing but not as well."

Cheers,
Dave
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Old 12-10-2005, 11:52 AM
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In addition, inPost #2 in this thread John Speake states:

"My understanding is that with a faulty Hall sensor, the igntion is retarded 6 degrees, because without a Hall signal, the signals from the knock sensors can't be processed. So the EZK retards the ignition 6 degrees "just in case" there is detonation."

Cheers,
Dave
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Old 12-10-2005, 12:14 PM
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Sorry to be banging on this thread, but I, too, was curious about what the Hall Sensor did so I've been looking around a bit.

I've found a reference in Adrean Streather's "Enthusiats Companion" on page 179 which reads:

"A Hall sensor in the primary distributor body monitors cylinder 1 top dead center. This allows the DME control module to synchronize the knock-sensor signal with the correct cylinder.

"The Hall sensor monitors the poistion of the rotor arm in the primary distributor. Its output is not dependent upon engine speed.

"If the Hall Sensor fails the engine will not start. The whole distributor assembly will have to be replaced."

This seems at odds with the statement by John Speakes where in he indicates that the ignition is retarded 6 degrees rather than preventing the engine from starting. Maybe it's the difference between "faulty" and "failed".

Any way, interesting stuff.

Cheers,
Dave
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Old 12-10-2005, 12:56 PM
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The hall sensor shows bad on a hammer test if the ingnition system is leaking spark .
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Old 12-10-2005, 01:28 PM
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The flywheel sensor measures RPM and can find TDC(60 - 2 teeth) but can't tell the difference between TDC on compression stroke or TDC on exhaust stroke, remember 720 deg. for a full 4 strokes.

The distributor hall sensor tells the DME which TDC is being seen.
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Old 12-10-2005, 01:39 PM
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The Hall sensor rarely if ever fails. A Hall sensor fault usually results from an
ignition RFI problem, i.e. electrical noise enters the wiring harness and the
DME ECM thinks it's a Hall sensor problem.

The 964 DME will run the engine fine with the Hall sensor disconnected.
Its function is ONLY for the sequential injection mode. The Hall signal is
NOT needed for proper operation of the knock timing control. The DME
always knows when the "relative" knock occurs without a cylinder
compression TDC, i.e. the Hall signal.
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Old 12-10-2005, 01:59 PM
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Springer
After I read your second post... DUH, my book is here,
There it was in Adrians book....

Also shows absolute proof I don't know what my car really should run like! I never had one before, never drove one before my own. I do think the car has lost a little tiny bit of performance since I got it (13 months/10,000 miles ago). This is the first time it has been in a Porsche proffesional's hands since I've owned it. Gonna be interesting when I pick it up to see what it's supposed to really feel like.
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Old 12-10-2005, 03:27 PM
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It may feel faster because you wallet is lighter if its a error code from an electrical leak and not the Hall sensor. There have been a few threads lately with the same error and turned out to be wires or coil arcing not the Hall sencor.
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Old 12-10-2005, 04:01 PM
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Originally Posted by Lorenfb
The 964 DME will run the engine fine with the Hall sensor disconnected.
Its function is ONLY for the sequential injection mode. The Hall signal is
NOT needed for proper operation of the knock timing control
Loren, With all due respect I am not sure this is correct, I had a broken wire on my dizzy hall sesnor and the car did undeed run, but not "fine", it would idle very rough, drop revs when the accelerator was touched, be difficult to get away at lights and the the power was noticeably reduced.
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