Knock Sensor question

sicksubie · #1 11-11-2007, 08:01 PM

After talking tonight and after letting Evil 1 drive my car I have a question.

If my knock sensors are reading vibrations from the blower and causing the engine to pull timing what prevents me from disconnecting them? I would throw a CEL obviously. I do know that I am creating no knock in my current condition. Jim ( evil 1) was saying that he always pulled the knock sensors on the cars he built to prevent them from inappropriately pulling timing.

SVXRide · #2 11-11-2007, 08:25 PM

given that they could potentially save your engine in the event that it is actually experiencing knock, why not try relocating them to a different part of the engine? what makes you think that the s/c is imparting a load on the engine block that resembles a "knock"?
-Bill

sicksubie · #3 11-11-2007, 09:49 PM

Because of their proximity to the blower and the amount of noise the blower makes....

Evil One · #4 11-11-2007, 10:09 PM

Also... I dont recommend ANYONE pulling the knock sensors unless they are on the safe side of their tune and monitor the engine VERY closely.
I have done it on almost all of my turbo engines because the ECU was VERY aggressive about pulling timing and the sensoers were bad about picking up a false positive on detonation.
Relocating them also works, but as I am still learning about the SVX I cant offer an alternative location to mount them.

However, that being said... I have pulled/disconnected them and picked up 30+ whp on a daily driver pushing 25 psi... that showed no sign of detonation when the engine was pulled down to upgrade the head gasket in anticipation of more power.

Jim

Trevor · #5 11-11-2007, 10:52 PM

There should be no reason for the knock sensors to react to noise from a blower. A weight is incorporated so that they are not sensitive to anything even remotely within the audio frequency range. Furthermore they a mounted to a large mass which would damp out extraneous indirect vibrations.

Hondasucks · #6 11-11-2007, 11:19 PM

I don't know how advanced the ECU is on an SVX, but most newer cars, if the ECU detects knock, it ignores it unless it occurs within a window around the ignition pulse, in order to prevent false signals from the knock sensor from affecting engine performance.

svxistentialist · #7 11-13-2007, 02:20 AM

Quote:

Originally Posted by Trevor

There should be no reason for the knock sensors to react to noise from a blower. A weight is incorporated so that they are not sensitive to anything even remotely within the audio frequency range. Furthermore they a mounted to a large mass which would damp out extraneous indirect vibrations.

What you are saying here Trevor may be correct in theory or at least desirable in theory, but it conflicts with the observed facts.

Graham had this problem with his Eaton blower. The ECU was pulling timing in a bad way. Initially we thought it was actual detonation. We discussed it with Lan. Some of the theories even included surface imperfections in the ceramic coating on the head contributing to localised hot spots. Bear in mind most or probably all of the US installations were using stock compression ratio. Graham was using a built engine with CR at 8.0 to 1.

The answer was more mundane. It was mechanical vibration picked up by the sensors as sicksubie and Evil One have noticed and deduced.

The actual source of the vibration that the sensors were "hearing" was the drive pulley for the blower. It had a loose key that we were aware of and eventually fixed.

The proof of the pudding was when the installation was put into my Version L, and everything tightened down, no loose pulley. The timing is not being pulled, full power all round.

As Trevor asked fellas, will it be possible to substitute more modern knock sensors in place of these piezo ones we currently use? Will the signal range be correct for the ECU to interpret?

If this made an improvement in a reduction of false positives and stopped the timing getting pulled, it would be worth the cost of the change.

Joe