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Registered
Join Date: Jun 2007
Location: Southgate Michigan, near Detroit
Posts: 30
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1988 knock sensor
i have a 1988S4, i took it to a bosch service center here in michigan, the car starts nice and seems to run smooth, however have never driven another 928 so i have nothing to compare it with, they say its very slow for this model and suggest that it needs knock sensors, or it may be a partly blocked cat. converter, my question to the group here is, can you verifiy if a knock sensor is bad with a multimeter? - wouldn't the cars computer light a trouble light if the know sensors were bad? - the last thing, has anyone replaced the knock sensors and "woken up" a dull engine? - the car has 34k miles on it, i did the timing belt and water pump, changed the caps, rotors, plugs "the new s4 plugs, i think thats what they are called" wires (oem) coils, k&N airfilter, smog filter. I don't mind spending the money i just want to see results - thanks to those that respond - Tom
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07-25-2007, 07:06 AM
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Network Native
Join Date: Jan 2007
Location: SoCal
Posts: 10,349
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Find a shop that KNOWS the 928 and has the box to talk to the computer and check the logs, which should show knocks or sensor errors.
http://www.eatel.net/~dslabat/mech.htm Also I think there are plenty of active 928 guys up in your area, go to one of the informal meeting and get some rides and opinions. Don't worry, you will be spending money.  No need to sprinkle it around mechanics while they learn about the 928.
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US 83 zinc metallic 5 spd, aka the nice car. Euro 85 black, 5 spd, the fast rough track car maybe car. SOLD Euro 84 red, AT, only car in garage in years, my parts car, soon to go last 7 years. |
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07-25-2007, 12:37 PM
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Join Date: Jan 2007
Location: Cambridge, England
Posts: 53
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There are two main performance killers on the 32v engines.
1) Igntion retarded by 6 degrees due to either a faulty knock sensor or the Hall sensor. It is only possible to test for knock or Hall faults with a Porsche specific diagnostic tool. e.g. Hammer, Spanner, PST2. However, sometines spurious knock/Hall fault codes can be stored. So, before reading codes, do a battery ground disconnect for a few seconds, and reconnect. Then test drive the car, hard. Then use the diagnostic tester 2) Weak mixture under acceleration and WOT due to an badly aged MAF. How many miles on the car ? And I would ditch that K&N filter - they can kill MAFs if overoiled after cleaning. |
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07-28-2007, 12:46 PM
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Join Date: Aug 2006
Location: Cincinnati, Ohio
Posts: 1,019
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The hall sensor connector is subject to easy breakdown in its mounted location. Having a hard retarded ignition will really kill your power...maybe 30 HP or more. I agree this is a really good place to start your checking.
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Kuhn Performance Technologies, LLC Big Gun: 1988 928S4 Twin Turbo, 5-SPD/LSD 572 RWHP, 579 RW ft-lbs, 12 psig manifold pressure. Stock Internals, 93 octane. Little Gun: 1981 928 Competition Package Twin Turbo, 375 RWHP, 415 RW ft-lbs, 10psig manifold pressure. Nikasil Block, JE2618 Pistons, 93 octane. |
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07-29-2007, 04:48 PM
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Join Date: Mar 2003
Posts: 37
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Tom -
Were you able to isolate the problem here. Did you replace the knock sensors? My previous 88' had the sensors replaced along with many of the items you already mentioned. Mechanic said it was one of the strongest 88' he had driven. O'...like john alread said...ditch that K&N filter. Tim |
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07-31-2007, 11:53 AM
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Join Date: Aug 2006
Location: Cincinnati, Ohio
Posts: 1,019
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With the K&N you just have to watch how much oil is used on them. Not so bad with the Turbo car bacause I have a long distance from the filters to the throttle body...plus it goes through two compressors and charge coolers...lots of places for oil to get trapped.
Fow what it's worth...I've watched 2 degrees of timing lay out 50 more HP on a turbo V8...this would not be so dramatic on a NA car, but coudl still be significant.
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Kuhn Performance Technologies, LLC Big Gun: 1988 928S4 Twin Turbo, 5-SPD/LSD 572 RWHP, 579 RW ft-lbs, 12 psig manifold pressure. Stock Internals, 93 octane. Little Gun: 1981 928 Competition Package Twin Turbo, 375 RWHP, 415 RW ft-lbs, 10psig manifold pressure. Nikasil Block, JE2618 Pistons, 93 octane. |
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07-31-2007, 02:51 PM
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Join Date: May 2007
Posts: 77
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Another performance killer on the '88 is the flappy. Pop the plug off and make sure it is rotating once you exceed 4000 RPM.
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08-02-2007, 04:11 PM
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