Yet another knock sensor thread.

[nothingbetter]

I've read every thread I could find on knock sensors and still havn't found my answer. I'm getting code 52, but only when my vaccum hits around 9-10 inches. I can drive around with no code but as soon as I hit that magic number the CEL light up. Then of course it stays on. Next time I start the engine its gone untill I hit said number again.

This makes me think its not the wiring because its not constantly on. I don`t want to re-wire it just because that might be it. I like to be sure of what the problem is before I fix it. (I hate wasting time, if it ain`t broke don`t fix it).

So assuming the wiring is fine, then the knock sensor is doing its job. I can`t see octane rating having an effect at 10inches of vaccum. So what else could be causing it to light upÉ

 

[jetjock]

Apparently you missed the threads where the parameters required to set this code are mentioned, that octane/knock has nothing to do with it, and that it's the only code to keep the MIL on until the key is cycled. Put another way your sensors and/or wiring are bad...

 

[nothingbetter]

I agree that I missed something. In my mind wiring is either good, or bad. That simple. Your telling me its bad. I'll take your word because I'm sure your more experienced than I am. So why does the CEL only turn on at 10ish inches of vaccum, shouldn't the wiring be bad regardless of engine vaccum? Is that when the knock sensors "turn on" or something?

 

[ifyouaint1sturlast]

I'd say the sensor is failing if your sensor or wiring is suspect at a certain engine behavior, as the sensor output changes, the wiring doesn't. Unless it's possible that when the signal from the sensor increases the wiring can't handle it because it's thin/frayed somewhere, but that's a long shot.

I'm not an electrical engineer.

 

[CyFi6]

The ECU looks for a signal from the knock sensors at a particular load and or RPM (not sure if it looks for one or the other or both), and when it doesn't see it, it turns on the MIL. Each time you turn the key off, this resets, and again at the specified load and rpm value it will look for a signal from the sensors, then it doesn't see it, and it turns the light on. Whether it's a sensor/sensors or its a wiring problem, the computer doesn't see an output from the sensor when it wants to, so it turns on the light. As JJ said, your wiring is faulty or you have a sensor/sensors that are dead. Put your meter on AC volts and probe the sensor wires at the ecu and go for a drive, I saw about .2 VAC IIRC out of a good sensor and basically nothing out of the bad one. Once you know which circuit is faulty (there are two), you can figure out whether it's the wiring or the sensor.

 

[nothingbetter]

Thanks for the input. I went out and bought the fancy sheilded wire that people are raving about. Sounds like I either do it now, or later when it does fail. I'll hopefully re-wire them tomorrow and hopefully fix the issue.

 

[nothingbetter]

so I was going to reqire it today, but, as bad as this sounds on my part, it turns out that its already been done. Theres 3-4 inches of wire after the KS before the shielding starts. Will that effect anything? It would also appear that the shielding has been grounded to a wire in the ECU. Not my prefered place to ground but whats done is done. I checked and the shield is grounding. I tried unplugging the KS's and the MIL acted the same. So survery says its the sensors themselves. Other threads I've read said in order to check a knock sensor I hold the engine at 2krpm (in neutral) hit the block with a hammer while looking at my multimeter and check to see if theres any voltage. Now, I'm no mechanic but this doesn't seem to be very conventional, can anyone back that up?

 

[jetjock]

Hammer on the block? Crack me up.

The ECU monitors the health of the sensors and wiring by listening for normal ignition events. Therefore a signal will be present just from running the engine. If the engine is off a tap on the manifold will do. A scope would be the best thing to use.

Edit: I meant for looking at the signal of course, not for banging on the engine. It's kind of sad that needs to be pointed out but after you've been around here a while you'll understand...

 

[CyFi6]

If the engine is off a tap on the manifold will do. A scope would be the best thing to use.

Edit: I meant for looking at the signal of course

:rofl:

 

[mk3_7m]

Yeah just get a pair of good knock sensors and if that doesn't work then must be a lousy wiring try getting a wire tester or multi-metre and test if the KS wires are live or not. check the connectors on the KS something might be loose.

 

[nothingbetter]

@mk3_7m - the wiring passes my inspection so I'm going to check the current sensors before I start throwing money at it. No sense buying 2 sensors if I only have to change 1!

@jet jock - I've been on a few other unlrelated forums before and understand what your going through. But my next question is, should I use a stethoscope or one of the scopes the eye doctor uses to beat on my engine with? I think the eye scope will make a bigger clunk. (that was a joke, haha) I'll check it tommorrow after work. Thats for the help!

 

[mk3_7m]

@mk3_7m - the wiring passes my inspection so I'm going to check the current sensors before I start throwing money at it. No sense buying 2 sensors if I only have to change 1!

@jet jock - I've been on a few other unlrelated forums before and understand what your going through. But my next question is, should I use a stethoscope or one of the scopes the eye doctor uses to beat on my engine with? I think the eye scope will make a bigger clunk. (that was a joke, haha) I'll check it tommorrow after work. Thats for the help!

Provided that both knock sensors aren't gone :naughty:

 

[jonahs_supra]

if you already have the shielded wire then why not do the rewire
previous owner of my car had done the rewire
he electrical taped the wires
which i figured he soldered the wires together
well turned out he just twisted and taped lol

 

[shaeff]

@mk3_7m - the wiring passes my inspection so I'm going to check the current sensors before I start throwing money at it. No sense buying 2 sensors if I only have to change 1!

@jet jock - I've been on a few other unlrelated forums before and understand what your going through. But my next question is, should I use a stethoscope or one of the scopes the eye doctor uses to beat on my engine with? I think the eye scope will make a bigger clunk. (that was a joke, haha) I'll check it tommorrow after work. Thats for the help!

By "scope" he means an oscilloscope.

 

[nothingbetter]

I tried checking the sensors but couldn't get any results from anything so I gave up and re-wired it since I already bought the wire. TA-DAA! No more light. Apparently my inspection of the wiring wasn't good enough. Live and learn I reckon. Dinglenuts (the original owner) has once again proven his lack of mechanical ability even though he claimed to be a mechanic (whats a torque wrench?). And I have once again proven my ability to overlook seemingly simple and obvious solutions. Thank you everyone for your input and putting up with another question.