CtSilver03Evo

iTrader: (9)

I disconnected my knock sensor completely this morning and drove the car about a mile up the road. The car is still detecting knock without it, and seemed to be picking it up quicker than normal.

...How is this possible without a knock sensor connected? Does this tell me my knock sensor is good, or bad? I'm confused at this.

Thanks!

Dynotech Tuning

iTrader: (12)

There may be a short in the cable going into the engine bay or the shielding for the cable isn't grounded and allowing noise to enter the signal path. It's easy to trace the knock sensor wires at the ECU, it's the only shielded cable (green insulation). It will have a single white wire coming out of the shielding. Try disconnecting that white wire from the ECU plug and see if it's still picking up the noise. The braided wire is supposed to be grounded when the sensor in plugged in. It basically intercepts any electrical noise and dumps it to a ground source before it can make its way into the signal path.



-Jamie

CtSilver03Evo

iTrader: (9)

Awesome. I will look into this later. Once I get results, how do I interpret the symptoms?

...If disconnected I still get noise, then what?
...If disconnected I get NO noise, then what?

Thanks Jamie!

CtSilver03Evo

iTrader: (9)

I'm super confused, because I found nothing wrong with the wire going to the ECU - so why did my car detect knock with no knock sensor?

Here's what I found:

1) With ECU connector unplugged and knock sensor unplugged, I get about 0.4Ohms from one end of the white wire to the other.

2) With ECU connector unplugged and knock sensor unplugged, I get OL from either side of the white wire to a ground.

3) With either end of the wire connected, or both ends connected - I get 4.39k Ohms from white wire to ground.

This being the case, can someone tell me why my car was picking up knock with the sensor unplugged?! Thanks!

tscompusa

iTrader: (31)

because the ecu freaks out with the knock sensor disconnected and not disabled in the periphery bit. ive never tried to disable it before in the periphery so you're on your own there.. but ive had customers forget to plug the sensor back in and you will get tons of knock counts that will appear.. even though its not real knock it retards timing to the point heat really can damage things.. so be careful.

wreckleford

iTrader: (2)

When you unplug the knock sensor the ECU defautls to the low octane maps and if you log it you will get a constant knock count of 8 or 9 once you pass a certain load, but it is not real knock. It is almost like an error code, i.e. constant knock of 8 or 9 = bad or disconnected knock sensor. The car will feel lame because it will be running off of the low octane map.

If you disable the knock sensor in the periphery it also disables the high octane maps so you will have to tune with the low octane maps.

Dynotech Tuning

iTrader: (12)

You can apply a dummy load on the circuit by installing a resistor into the knock sensor plug to simulate the knock sensor load. Take one of these resistors and connect one end to the white wire and the other to ground. The shielded wire on the knock sensor cable going to the ECU will also need to be grounded.

It should allow the ECU to do business as usual while eliminating any knock sensor activity, for testing only.

-Jamie

tscompusa

iTrader: (31)

i dont think this is 100% correct. when you unplug it, it does more then just default to the low oct map.. reason i know this is because, my low oct map would not cause a car to act like my customers described to me when this incident occurred when they forgot to plug in their knock sensor.

the car was barely driveable, it backfired, sputtered, shot flames, etc.. my low oct map isnt extremely that different as opposed to the high to the point those issues would occur..

so i believe the ecu is still doing something to the car.. if it were just resorting to low oct map then the car would be driveable still and no issues.. just alittle down on power based on how conservative / safe the low oct map would be set.

now it makes sense what you said about the ecu resorting to the low oct map once its fully disabled in the bit.. because then there is no need for 2 maps low/high.. the only reason low/high exists is for the sensor to be the judge on what one should be used.. knock protection etc. <-- not 100% explained but others will know what im saying.

evolvedevo91

iTrader: (3)

Adding info to this thread for anyone who ever needs it.
My knock sensor went missing (under some mysterious circumstance between a couple of different shops while car has a variety of things done to it)
Anyway, my car drove completely normal during the initial 1,500 mile motor break in without any knock sensor in the car at all.

Ended up the knock sensor connector was missing in addition to the knock sensor itself. But now all of a sudden the car is undrivable like as described by tscomp. It sputters ridiculously above anything more than 2000 rpm. (even under no load when the car is in neutral) I am awaiting a knock sensor from the dealer in hopes this is my issue.

merlin.oz

Check to see what spark timing is doing, probably some negative value now.