MazdaSpeedDan

iTrader: (4)

Hey guys, read the FSM and found the knock sensor part but it doesnt say what it does when its bad, only that it retards timing or something of that nature but doesnt really get into it.

Previous owner was nice enough to take the CEL light out for me, like literally take the bulb out so thats why I was never throwing any codes during the self diagnostic test. Apparantly im throwing a 5 code which is bad knock sensor.

Has anyone had a bad knock sensor and if so what were the effects of it? Limp mode? Bucking? Nothing?

Help is much appreciated and thanks.

AzEKnightz

iTrader: (24)

well, FSM already explained it. Retards timing = lack of power and sluggish spooling in other terms.

if you have a code for that, just make sure the connection on the knock sensor is good. Then replace the sensor.

-AzEKnightz

ppritchard

Having the same code.
Just post on the "wanted to buy" parts for sale, several members had knock sensors for sale.

Ours started after changing the plugs, likely messed up the wire somewhere along the way.

MazdaSpeedDan

iTrader: (4)

What symptoms did your car have?

ppritchard

No performance issues -- but we continue to get sporadic Check Engine lights with the knock sensor code and sometimes with the solenoid error.

Bought solenoid and knock sensor and will install them next week. If that doesn't fix it, who knows.

riwanika

iTrader: (1)

I have the same code and need to smog, did replacing the knock sensor get rid of the CEL and if not what did you do to fix it?

MazdaSpeedDan

iTrader: (4)

Yes replacing the knock sensor with a good knock sensor will take away the CEL.

wstrohm

Our '94 threw no codes, but the OEM knock sensor leaked a gooey stuff down onto the spark plug and wire end. So I replaced it... however, I tested both the old and new sensor per the FSM (page F-171) and neither one budged a voltmeter on its most sensitive scale, when the lift bracket was tapped with a hammer.

I think the sensor is a piezo-electric device (crystal) that generates a voltage pulse when excited by a vibration, but if so, one would never see a dc voltage. I think you would need an oscilloscope to actually see whether it is working. (I have a problem believing that the knock sensor fault monitor circuit actually works.)

riwanika

iTrader: (1)

Well I ordered a replacement knock sensor so hopefully that works.

DaleClark

iTrader: (55)

I think the factory ECU just checks the resistance of the circuit to ground. If the wire is broken or damaged or it's not plugged in you get a code. That's about it.

Dale

wstrohm

IIRC, I checked the electrical resistance between the new knock sensor's electrical connector and its case (ground) before installing it. The meter showed an open circuit, or at least greater than 10 Megohms. So I think that the fault monitor circuit would only be capable of seeing a short circuit to ground as a fault. Please, someone tell me if that is incorrect!

riwanika

iTrader: (1)

This may sound dumb but i had the knock sensor and the power steering pressure sensor connectors swapped and when the pump felt a certain amount of feedback from the steering wheel it would trigger a voltage or something through the connector and turn off the CEL for the knock code. I was really confused untill i found out that my wires were switched. Would it be possilble to feed a voltage through this wire to temporarily clear the code, say if someone needed to pass smog? jw

MazdaSpeedDan

iTrader: (4)

Maybe take out your CEL light for Smog?

riwanika

iTrader: (1)

I thought about that but they check to see if it lights up on ignition. I haven't found a place that will give me some wiggle room on the visual inspection. All i know is as soon as I get that certificate and my tags all this smog stuff is coming off, especially the advanced warm up system, that thing is embarrasing in public...

riwanika

iTrader: (1)

Fixed! Well I would like to post my findings. After an extensive search of my wiring harness i found that the wire for the knock sensor had been squished against the edge of the solenoid rack by the alternator and was grounding its self out. After some careful splicing and trimming I was able to attach a new shielded connector and hook up my sensor. It's all good! Now I can go pass that smog and get my title...