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How do I bypass knock sensor on RENIX?

S

stockli

NAXJA Forum User
Location
Ft. Collins
I have an 89 limited and just popped a 94 block in her. On the way out a banged the old knock sensor and broke it apart.

Im too cheap to buy a new one especially since I would have had to tap the new block to install it anyway.

How would I go about bypassing this sensor? Can I clip the plug and wire the leads together? Or clip and cap each wire going into the connector to keep the circuit open?
 
The sensor doesn't generate a signal unless something's wrong - I'd just leave the wiring disconnected, put a baggie over it, and tie it back out of the way.

However, if you run into issues with carbon buildup or really crap fuel, the knock sensor can save you some engine damage. I believe it's a blind hole, M10-1.5x15 or 20m/m (it need not go through, and it's better that it doesn't.)
 
I'm with 5-90 on this.

Seems though I read somewhere a post that somebody had a similar situation--no place to mount the sensor--and they ended up just plugging it into the harness and then strapping it up out of harms way. I don't remember if they had a problem and that is why they had to plug the sensor into the harness.

Also, if you decide to drill and tap, the torque on the knock sensor is critical--10 N*m or 89 in lbs.
 
5-90 said:
The sensor doesn't generate a signal unless something's wrong - I'd just leave the wiring disconnected, put a baggie over it, and tie it back out of the way.

However, if you run into issues with carbon buildup or really crap fuel, the knock sensor can save you some engine damage. I believe it's a blind hole, M10-1.5x15 or 20m/m (it need not go through, and it's better that it doesn't.)
Click to expand...

I tend to disagree with your comment 5-90. I worked on developing a piezo technology used for knock sensors. They are a high impedance vibration sensor, much like a high Z microphone. That is why the wires are shielded. The Z is so high that it is easy to induce noise into the circuit even with a working knock sensor. If you are going to can the sensor, your best bet would be to hook a 1k ohm resistor across the wires or even short them, otherwise if left open it picks up enough noise to fool the ECU into thinking that the engine is pinging or suffering from detonation and will back off the timing. If you short across the sensor, it will advance the timing as far as it can. While neither is great, in most situations, especially here at high altitude, the advance in timing helps.
 
So twist them up and tape them or run a restistor between them, those are my best options?

Im going to just not plug anything in and see what happens if there is trouble Ill probly just twist them together.

Thanks!
 
old_man said:
I tend to disagree with your comment 5-90. I worked on developing a piezo technology used for knock sensors. They are a high impedance vibration sensor, much like a high Z microphone. That is why the wires are shielded. The Z is so high that it is easy to induce noise into the circuit even with a working knock sensor. If you are going to can the sensor, your best bet would be to hook a 1k ohm resistor across the wires or even short them, otherwise if left open it picks up enough noise to fool the ECU into thinking that the engine is pinging or suffering from detonation and will back off the timing. If you short across the sensor, it will advance the timing as far as it can. While neither is great, in most situations, especially here at high altitude, the advance in timing helps.
Click to expand...

Thanks - I didn't know that the KNOCK was a Hi-Z sensor.

Question - would it also be a valid "block-off" to wrap the socket end with aluminum foil, make sure it connects to the foil wrap for the wiring, and then bag that up?
 
5-90 said:
Thanks - I didn't know that the KNOCK was a Hi-Z sensor.

Question - would it also be a valid "block-off" to wrap the socket end with aluminum foil, make sure it connects to the foil wrap for the wiring, and then bag that up?
Click to expand...
That would help, but poking a 1k resistor between the terminals first would make it even better.
 
I would personally find a replacement at the JY, but they are getting rare. If there would be one on an 88 MJ (I think there would be) I can pull one and throw it in a bubble mailer or 5 dollar flat rate box for you, but it'll be untested junkyard stuff. Aside from that I would agree with Tom on this one and say throw a 1k resistor across it to keep it from picking up random engine bay noise.
 
Thatd be great, jsut pm me and we can set that up.

I just dont want to have to tap the block. I want to make sure there are no threads, if there is then I may try and use the one off the MJ is not Im not gonna plug anything into it and go from there.
 
Last edited:
Ok, I'll throw a reminder to pull it in my phone for tomorrow morning.
 
I tapped my 98 block when I did my swap, it wasn't a big deal at all. It is a little scary drilling into a block hoping that you don't go too far, but if you make some kind of a stop then it's really easy.
 
Sorry man... Checked the mj and an 89 limited that showed up since thursday, could not find it on either
 
kastein said:
Sorry man... Checked the mj and an 89 limited that showed up since thursday, could not find it on either
Click to expand...

Is there still a round boss down by the oil sump rail? I don't think they ever changed/removed that from the mould blanks - it just went unmachined in later engines.

If you go through, I'd imagine you'd be fine - I just want to point up that it's not necessary to do so. If you're worried about going through, pack the drill flutes with grease to catch chips (ditto the tap.) Seal with whatever you like - RTV should be sufficient. The mechanical connexion the sensor requires will be had when the base of the sensor touches the surface of the boss and the sensor is torqued into place.
 
Thanks anyway for looking kastein!

5-90 thanks for the tips. There is a hole there but last time I saw it it was full of mud so I cant be sure it was threaded.

I will be down workin on it again this coming week. I will let you all know!
 
5-90 said:
Is there still a round boss down by the oil sump rail? I don't think they ever changed/removed that from the mould blanks - it just went unmachined in later engines.

If you go through, I'd imagine you'd be fine - I just want to point up that it's not necessary to do so. If you're worried about going through, pack the drill flutes with grease to catch chips (ditto the tap.) Seal with whatever you like - RTV should be sufficient. The mechanical connexion the sensor requires will be had when the base of the sensor touches the surface of the boss and the sensor is torqued into place.
Click to expand...
Hmmm, apparently I'm just an idiot and was looking in the wrong place :wierd: I was checking for it up near the head/valve cover.

stockli said:
Thanks anyway for looking kastein!
Click to expand...
No problem, apparently I was looking in the wrong spot... if they are still there when I go again, I will try a second time.
 
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