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Old 07-27-2010, 01:05 PM   #1
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False Knock** What could be causing it?

Hi Everyone,

I've recently installed a JRSC the SVT and have bought the J&S to monitor knock.

I am in the process of tuning the car with Tom and have noticed my knock sensor goes of anytime I ease into the throttle regardless of RPM. The J&S was set at 50% at this time.

I've done numerous datalogs and even filled up with higher oct gas but the knock sensor behavious seems the same. I have turned down the J&S sensitivity to about 30% and tested the sensor by hitting the block. It reads knock, but at this low of a setting it doesnt go off when i ease into the throttle anymore.

This leads me to believe this is false knock from noise.

Is my J&S sensitivity too low to save my motor from potential knock?

What could be causing this false knock? Anyone have similar issues?

I have a slighly bent header, and a loud exhaust, I've been driving the car and everything seems like its running fine. I just want to be safe and have the J&S doing its job since it was an expensive investment.

Thanks,

Adam


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Old 07-27-2010, 02:40 PM   #2
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Issues with jrsc
loose or vibrating exh where its hitting or vibrating on engine
idler pulleys
bad ks sensor

Tom
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Old 07-28-2010, 11:01 AM   #3
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Excessive tappet clearance could cause this, as well.
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Old 07-28-2010, 01:46 PM   #4
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I've heard a timing belt tensioner pulley do it as well. It will actually sound like an audible engine ping or knock at times.
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Old 07-28-2010, 04:48 PM   #5
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Yes, I have this issue. I didn't notice it until after I installed a HFC and after I got a dyno tune.

Someone suggested capping off the vac line on the J&S unit to decrease the false knock at low speeds? Thoughts?
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Old 08-04-2010, 11:52 AM   #6
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Piston slap on decel or light engine loads can cause false knock.

For this reason, the unit ignores the knock sensor if it senses more than five inches of vacuum.

To activate this feature, connect the vacuum line to the unit.

This also enables the Boost Retard feature, so you will have to turn the "Rate" knob fully CCW unless you plan on using it.
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Old 08-04-2010, 06:15 PM   #7
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Quote:
Originally Posted by focus311 View Post
Yes, I have this issue. I didn't notice it until after I installed a HFC and after I got a dyno tune.

Someone suggested capping off the vac line on the J&S unit to decrease the false knock at low speeds? Thoughts?
If you have the J&S set on the sensivity set to half and you have lights then you more then likely have knock , Dyno shops argue with me all the time about thats to little of timing and it wont run well but thats BS and it makes the same load with my tune as the tunes with to much timing

The OP that started this thread had spark (J&S Lights) tipping into the throttle and at low rpm and mid load , he sence found the issue a bad pully and changed it and now we are adding timing back in

Tom
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