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Discussion Starter #1
I'm getting knock codes but no Check Engine Light, which I understand is normal for a bad knock sensor or knocks heard for any reason. I get no other codes. The engine does knock under load especially in hot weather. Premium gas helps a lot but doesn't eliminate the knock entirely. Mileage has dropped from 32 MPG to 25 MPG highway while around-town mileage is the same as it has been (25, or 23 with air conditioning).

I have a replacement Knock Sensor and finally found the sensor on the engine (the Haynes book has no picture). How the heck do you get at it to replace it? Every thread I have found here has said "replacing the knock sensor was a pain" but doesn't actually reveal the trick finally used.

I can get a 12 mm 12 pt wrench on the bolt, but it isn't long enough for me to get more than one finger on the wrench. My sockets etc. do not fit since there is a hose right behind the knock sensor bolt. I have a 12 mm wrench with a slip-on extension for leverage from my motorcycle kit, but it is straight and I need the little angle provided by the standard 12 pt wrench to clear the brackets.

I am approaching it from below with the car jacked up as high as I can.

Is there a special tool? Something I need to remove? A super-secret access panel?

Thank you!
 

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It may be easier to get at with the giant "Y" bracket removed.
It's the giant bracket that looks like a "Y" bolted to the intake.

I pussied out and payed to have mine replaced. I'm ashamed, but the price was well worth keeping my sanity.
 
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It may be easier to get at with the giant "Y" bracket removed.
It's the giant bracket that looks like a "Y" bolted to the intake.

I pussied out and payed to have mine replaced. I'm ashamed, but the price was well worth keeping my sanity.
yeah it is a pain to get at.


i just lengthen the wire, and put the knock sensor on the front of the cylinder head (exhaust side). probably not the best thing, but it works. i wouldn't recommend it since i don't want to get yelled at for people blowing their engines up. (just covering my butt on this. knock sensor is just a microphone)
 

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Discussion Starter #4
yeah it is a pain to get at.


i just lengthen the wire, and put the knock sensor on the front of the cylinder head (exhaust side). probably not the best thing, but it works. i wouldn't recommend it since i don't want to get yelled at for people blowing their engines up. (just covering my butt on this. knock sensor is just a microphone)
I'm liking this answer more and more! Especially since my replacement is a used item and might not last very long. At least the next time I'll be able to get at it.
 

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Discussion Starter #5
It may be easier to get at with the giant "Y" bracket removed.
It's the giant bracket that looks like a "Y" bolted to the intake.

I pussied out and payed to have mine replaced. I'm ashamed, but the price was well worth keeping my sanity.
Worth considering, and at least I'd be able to get more fingers on the wrench. I haven't seen any way to get more length for leverage.

Thanks!
 
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I'm liking this answer more and more! Especially since my replacement is a used item and might not last very long. At least the next time I'll be able to get at it.
it seems to work fine there. i wired in an audio jack so i could use audacity as a makeshift oscillator scope. looked like normal engine noise...
 

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Discussion Starter #7
I ended up leaving the old sensor on the back of the engine block and mounting the "new" one on the driver side of the block behind the distributor and in front of the throttle body. The wire reached without splicing. I torqued to 15 ft-lbs.

I cleared the 34 codes and went driving. Same old thing, I'm getting a rattle on acceleration below 3K. I wish it could tell me whether it thinks the sensor is bad or is just hearing knocks with that code 34.

I haven't checked the codes again but bet (since it is acting the same) it has some 34s again.

Is there something else I should check, which would cause knocking but not throw other codes? It's a 95 G20t auto.
 
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I ended up leaving the old sensor on the back of the engine block and mounting the "new" one on the driver side of the block behind the distributor and in front of the throttle body. The wire reached without splicing. I torqued to 15 ft-lbs.

I cleared the 34 codes and went driving. Same old thing, I'm getting a rattle on acceleration below 3K. I wish it could tell me whether it thinks the sensor is bad or is just hearing knocks with that code 34.

I haven't checked the codes again but bet (since it is acting the same) it has some 34s again.

Is there something else I should check, which would cause knocking but not throw other codes? It's a 95 G20t auto.

when was the last time you did a tune up?
 

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Discussion Starter #9
Roughly speaking, never.

This is my first ODB-I car so I guess I'm treating as magic regarding diagnostics. I'll go look up the tuneup procedure.

Thanks for all your help!
 

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I ended up leaving the old sensor on the back of the engine block and mounting the "new" one on the driver side of the block behind the distributor and in front of the throttle body. The wire reached without splicing. I torqued to 15 ft-lbs.

I cleared the 34 codes and went driving. Same old thing, I'm getting a rattle on acceleration below 3K. I wish it could tell me whether it thinks the sensor is bad or is just hearing knocks with that code 34.

I haven't checked the codes again but bet (since it is acting the same) it has some 34s again.

Is there something else I should check, which would cause knocking but not throw other codes? It's a 95 G20t auto.
First thing the knock sensor does note trip a code 34 because your engine is knocking, it trips a code 34 when there is some sort of short and im my own personally experience with this the knock sensor shielded signal wire usually ends up shorting to the shielding wire which is ground.

Look at post 3 read it an apply it.

http://www.sr20forum.com/general-sr20/213046-knock-sensor-junk.html
 

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Discussion Starter #11
First thing the knock sensor does note trip a code 34 because your engine is knocking, it trips a code 34 when there is some sort of short and im my own personally experience with this the knock sensor shielded signal wire usually ends up shorting to the shielding wire which is ground.

Look at post 3 read it an apply it.

http://www.sr20forum.com/general-sr20/213046-knock-sensor-junk.html
Wow, OK.... That's going to require both in-depth reading and me finding my multimeter.

Thank you!
 

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I've done about 10 of these on sr20 engines. PRE-94 cars don't have that big black "Y" bracket on the back of the engine, which makes changing the knock sensor pretty easy. WITH the "Y" bracket on 94 and up G20's, it takes me about an hour to change the sensor. There's 4 mounting bolts, two on the intake manifold, two on the lower part of the engine (IIRC, one has to be put back because it's part of the axle carrier bracket). There's also alot of emissions crap connected to the bracket. You can fenagle that bracket out without removing anything else. It's a bitch, but it comes out.

You have to use a wrench (not a ratchet) to take the sensor off, i believe it's a 12mm bolt.

Once you have the bolt off, fish the sensor and harness plug up into the engine bay. Take the sensor off the harness, and hook the new sensor up.

Fish the new sensor down and install the bolt. The sensor plug should be between 45 and 90 degrees (parallel to the ground, or 45 degree pointing towards the ground). like "-" or "\" if that makes sense. Now the funny part is the FSM says to torque the bolt to around 15 or 20ft/lbs. You can't get a torque wrench up there, so just be moderate when installing. Too much torque can crack the plastic on the sensor.

If you think it's a harness problem, DON'T HACK IT. Buy a new OEM injector harness or get one from the junkyard. That harness isn't meant to be spliced or soldered in to.

Also, DO NOT relocate the sensor. It will give false readings. Do it the right way, like it came from the factory.

eBay has the sensors for like $50 (OEM ones) and you can get a new injector harness for like $30 or $40. So for under $100, you are fixing it the right way. That's the way to go.
 

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Also, an easy way to extend that wrench is to put a big socket on the end of the wrench, and an extension bar on the socket. Voila. That's how i do mine :)
 

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I wish i still had the pics of how I fixed mine and about 6 other S13 240sx with a short to ground in the shielded wire, it would be nice to replace teh whole harness with a new on ebut in the case of teh S13 it would include buying a whole new harness. When and if you repair you must make sure to repair it and keep it just like OEM was, keeping the shielded portion together and separated from the signal wire that resides inside of this shielded wire, a lil tricky but i've done it every time with success.
 

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Discussion Starter #17
Your car is OBDII.
Are you certain? I thought that started in 1996. Mine is 1995. I do see that some sites say the changeover was in 1994.

I get 2 digit codes on the CEL, if that's any help.
 

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Discussion Starter #18
Well, I finally got to the plugs this evening and they look pretty rotten.

They are Bosch platinum and they have a crusty brown coating on the side electrode and center insulator. They were also wet with unburned oil. The center electrode was not visible. Every plug had similar erosion.

I replaced them with a set of stock NGKs but haven't had a chance to drive them yet. The Boschs have at least 20K miles (probably more).

Looks like I have oil leaking into the combustion chambers?
 

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Discussion Starter #19
Are you certain? I thought that started in 1996. Mine is 1995. I do see that some sites say the changeover was in 1994.

I get 2 digit codes on the CEL, if that's any help.
I see there's room for confusion. I don't have the phrase "ODB-II compliant" (just "conforms to 1995 emissions standards" or something like that) on the under-hood sticker. I'll check the connector tomorrow when I have some light.
 
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I see there's room for confusion. I don't have the phrase "ODB-II compliant" (just "conforms to 1995 emissions standards" or something like that) on the under-hood sticker. I'll check the connector tomorrow when I have some light.
nissan started the obd 2 conversion in '94. federal law didn't require it until '96 in a way it has both obd 1 and obd 2 systems in it.

you could call it obd 1.5 since it'll give the codes like obd2, but still blink them out like obd1
 
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