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Do bad knock sensors affect performance?

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Old 01-07-2002, 04:00 AM   #1
BlackbirdZ07
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Default Do bad knock sensors affect performance?

A most disturbing experience happened to me today.... I got seriously killed by a Porsche 928. I could tell by the taillights and wheels that it was later model one (probably at least 1989, S4) and those have lots more power than the older ones. I also hit the rev limiter in 1st, but I didn't think I'd have that much of a problem. My car is a '92 LT1 6 speed with 3.54 gears, stock except for a K&N, throttle body airfoil, and Ed Wright fastchip.

I've had the "check engine" light on recently; and the cause is a code 43 knock sensor. I honestly don't know whether the light was on during the race, but it probably was. My question is how much will a malfunctioning knock sensor affect performance? Either way I'll replace it as soon as I can now. And if anyone knows someone who ownes a white 928 in Dallas who has been acting a bit smug lately I want a rematch!!!! :boxing
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Old 01-07-2002, 05:29 AM   #2
Bill Reid
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Default Re: Do bad knock sensors affect performance? (BlackbirdZ07)

Yes, a faulty knock sensor and/or circuit can considerably affect performance. In my case (85) if the knock sensor is not working properly after the ECM goes into closed loop it will set a code and put the car in "limp home mode".
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Old 01-07-2002, 09:03 AM   #3
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Default Re: Do bad knock sensors affect performance? (billreid1@home.com)

What he said. I had that problem last summer, but it turned out to be the ecm, not the sensors. Of course, I didn't figure this out until I changed the knock sensors, but they weren't too expensive. When the code 43 was being set, the gas mileage went from 22 to 14, and the car had no power at WOT. Swapped the ecm, and all is back to normal.
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Old 01-07-2002, 09:34 AM   #4
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Default Re: Do bad knock sensors affect performance? (BlackbirdZ07)

That don't sound right. Saturday we had a Porsche show up at the dyno. I think it was a Carrera or something like that, his supercharged car only put down 270 hp. Your stock LT1 should put out as much if not more. Then it just comes down to a question of weight. I don't know my Porsche's that well so I don't know what kind of HP your "friend" should have been making, but it sure doesn't sound right.

On the way home from the dyno we met up with a Porsche 944, he was a joke. He kept trying though, how many times do you have to get destroyed before you just give up?

That being said, yes a bad knock sensor can seriously hurt performance. If it is actually setting a code I'd say your car is in limp mode so it doesn't hurt anything. Otherwise it could be possible for a knock sensor to pick up false knock and retard your timing greatly, hurting performance.
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Old 01-07-2002, 10:57 AM   #5
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Lee Hamner
Default Re: Do bad knock sensors affect performance? (Nathan Plemons)


If the computer thinks the knock sensor is bad, it will retard timing hideously to be on the safe side. This will make the car seem sluggish. Better for it to do this than permit knock, which can lead to expensive-parts-need-to-be-replaced-syndrome.
A 928S4 Porsche is a NA water cooled 4Cam front engine V8. Most were Automatics, and they were heavier than a C4. I think a healthly LT1 should beat it. A supercharged Carrera is an aftermarket mod on a rear engined flat-6 (the 911 bodystyle cars). The cars to fear there are the PCA racers who have the twin turbo 3.6 motors set up to club race. These can usually be easily recognized as your passenger says, "Dang- Billy! Those wheels musta cost more than my house!"
Lee
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