Knock and revolution sensors

[Trini 94Q45]

Hi Guys,

I've recently discovered this site through an ebay link and can't get enough. I have a 94'Q, I'm a mechanical novice and is always willing to learn, my first question is, what's the function of the knock and revolution sensors?. Keep up the great work guys.....

[maxnix]

Welcome aboard, Trini.

nnot to be coy, but read the original posts by q45tech concerning these and other functions and you will be richly rewarded. His explanations and insights are mcuh more detailed tahn I could reproduce.

[bullittandy]

Hi Guys,

I've recently discovered this site through an ebay link and can't get enough. I have a 94'Q, I'm a mechanical novice and is always willing to learn, my first question is, what's the function of the knock and revolution sensors?. Keep up the great work guys.....

The knock sensors are small "microphones" that "listen" for engine ping/knock/pre-ignition and then "tell" the engine's computer to change/retard the ignition timing until the engine stops pinging etc. Pinging is caused by low octane gasoline, high temp, heavy loads, carbon build up in the engine.

[CINNALOCKS]

Thanks bullittandy for such a short precise explaination. I too am a novice and some times shun away from asking things that may seem mundane or stupid to the more knowledgable. For us that have not had a history in the mechanics of cars, let alone the Q, it is good to be able to get help needed for everyone to get it. The pictorals are the so helpful. I have gotten so much info here but I need to hear it more than once usually and sometimes from more than one perspective. Nothing I have read or heard simplified the function of the sensors. Now I got it too!!!!

[Q45tech]

Pinging can only occur prior [-10-+5 degrees] to the normal pressure peak at 16 degrees after TDC, thus the ecu switches the microphone on for a very small time period every 90 degrees of engine rotation so the system isn't fooled by other normal noises in the engine.

Q45 have 2 knock sensors [one on each head and 2 separate circuits in ecu to increase sensitivity and resolution, as alternate banks fire.

Pinging is bad because it occurs at TDC when the extreme pressure would drive the piston/rod straight down into the crank bearing instead of later at an angle to turn the crankshaft.

Maximum torque is achieved just shy of the point of pinging. but not above the ping threshold where advance is reduced. A fine line.

Pinging has a specific frequency signature based on the bore diameter, much like the resonance of a pipe organ except it is 4-7 Khz.

If you know these things and these numbers, you know as much as an average Master Tech.

[Trini 94Q45]

Hey Guys, Thanks a lot for that info guys, I really appreciate the imput from everyone. So much for knock sensors and their function, now part two of the original question was about the revolution sensor, it's function and if defective what are the effects on the performance of the car.

Holla back !!!!!!

[cabal1024]

I believe you are referring to the camshaft position sensor? I believe this is responsible for timing the firing of the spark plugs.

[elwesso]

Yeah, theres a few revolution sensors you could be talking about.. Camshaft position sensor (maybe?), turbine revolution sensor, vehicle speed sensor, to name a few....

The Cam sensor replaces a distributor on a regular engine.... Instead of having points that spin around on a rotor, it reads pulses....

[Q45tech]

The CAS has 3 different sensors inside and provides 3 different pulses, 1 every degree of camshaft rotation and 2 every 90 degrees [one from a magnet coil and the other electro optical like the 1 degree signals.

The CAS is the master time clock for ecu and enables ecu to know when piston #1 is at TDC and thus every 1 degree.....................how ignition timing is set accurate within 1 degree.

1 degree of cam rotation is = to 2 degrees of cranksgaft rotation.

[Trini 94Q45]

Does the transmission also carry a revolution sensor?

[elwesso]

Yeah, it has the turbine (torque converter) revolution sensor and the vehicle speed sensor...

[Q45tech]

Remember the front of TC is bolted to flywheel so it turns at engine rpm which is reported by CAS.

The constantly slipping* [except at lockup] rear of TC is reported by the REVOLUTION SENSOR................the output of transmission is reported by the speed sensor, the tire/wheel rotation is reported by ABS sensor or sensors [3 without TCS or Active, 4 with]..

*at idle, stopped in drive the front of TC is spinning at 650-1500 rpm whereas the rear is stopped. = lots of heat from churning ATF.

[Trini 94Q45]

Hey thanks guys, I like the way you simplified that.