Mechanics

KNOCK SENSOR

1994 Infiniti J30

Replaced EGR which improved performance but did not replace knock sensor. Diagnostic indicated a bad EGR & Knock Sensor. At the time the engine began to make the knocking sounds, the steering and brake lost the power boost. The knocking sounds are present at an idle and when the engine is spun up. The engine noise does not change to any significant degree at idle or when revved up. Will replacing the knock sensor fix or alleviate this problem?
I'm a new visitor to your website. Thanks for your assist.
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DJ Scott
April 30, 2013.




The first thing you must understand is diagnostic fault codes never say to replace parts or say parts are bad. They only indicate the circuit or system that needs further diagnosis. About half of the time the sensor referenced in the code is defective but half of the time there could be a corroded splice, stretched or corroded terminal in an electrical connector, or a broken or grounded wire. There are also numerous potential codes related to both of those sensors. Some describe a defective condition with the electrical circuit. Some describe an unacceptable condition that is being reported by a sensor that is working properly.

In the case of the knock sensor, if you can hear a knock in the engine, the sensor is supposed to report that. It is supposed to detect spark knock but it will respond to mechanical problems inside the engine too. In response, the Engine Computer will retard ignition timing in an attempt to stop that knock. That will result in low engine power. Replacing the knock sensor won't fix the problem it is detecting.

Caradiodoc
Apr 30, 2013.
Thanks, that does shed some light on the codes and how to assess the level of repair involved. Your assessment also explains the lack of power. However, the engine makes a mechanical knocking almost like a rod knock but the sounds is coming from the top end. Can a bad sensor and EGR cause valve problems? The original engine had about 320K on it when I replaced it with a used engine that had 94K. I replaced the pulleys and timing belt and had an Infinity Dealer set the timing. I put maybe 1,000 miles on it before the engine began making the top end noises. Any ideas on what that could be?

Thanks.
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Tiny
DJ Scott
Apr 30, 2013.
Can't help with the cause of the noise but anything up high is less serious than a rod knock. Often the dealer's engine specialist can tell you the cause by listening to it. Things I've run into in the past include piston slap, a cracked rocker arm, and a worn camshaft thrust plate that allows it to walk back and forth and bang on that plate.

Some engines use spring-loaded tensioners for the timing belt that also use pressurized engine oil. If that oil passage is plugged or the spring is broken they can let the timing belt slap around.

Don't overlook a loose vibration damper. That will cause a double knock each engine revolution.

Caradiodoc
Apr 30, 2013.

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