Renix Knock Sensor

[HOrnbrod]

I know this sensor is supposed to tell the Renix computer to retard ignition timing when it detects engine ping / knock. But I've always wondered just how it did this. It screws into the block and senses what? (vacuum, pressure?) through the orifice? It has two pins. What is connected to these pins, and what happens to make it change ignition timing? 

 

On an HO you can change timing by physically sliding the CPS magnetic pickup on the mount so the flywheel pulses are seen by the ECU earlier or later, but how does the Renix knock sensor do it? It seems like a good thing to have, and I've always been curious as to why it or something similar wasn't used on the Chrysler system.

[fiatslug87]

Senses vibration, the hole it screws into is a dead hole.

Edit: What? Something RENIX that's useful?? :)

 

 

[DirtyComanche]

It's an accelerometer or velocimeter and it has been filtered for the specific frequency of detonation.

 

Honestly, they're standard equipment on most FI setups.  I have never been able to wrap my head around the HO not having one.

[Eagle]

It's an accelerometer or velocimeter and it has been filtered for the specific frequency of detonation.

Yep.

 

And you can run a rough test of it by having someone watch the timing mark with the engine running, and have another person tap the block next to the sensor with a hammer. If the timing jumps, the sensor is working.

[HOrnbrod]

Senses vibration, the hole it screws into is a dead hole.

Edit: What? Something RENIX that's useful?? :)

 

 

 

 

Thanks Mike.

 

If a knock is present, the ECU will retard ignition timing by a predetermined value on any cylinder or a combination of cylinders.

 

Interesting. That's pretty impressive if true. The output has to be tied into the CPS circuit somehow I would think. I guess the volume of the knock sound determines how many cylinders will be retarded. I'll have to find a schematic of it's wiring................

 

Also, I haven't seen any way to test them, except by replacement.

[mikekaz1]

Hmm I'm actually kinda interested in this too... since I'm running an HO ecu but I have a renix block with the knock sensor still hanging loose next to it. If I could possibly splice and reconnect it with some positive results.

[DirtyComanche]

The ECU is what does the magic with it.  The HO ECU has no provisions for this.

 

But somebody in this thread hates the Renix and thinks it's 'weird', his loss.

[HOrnbrod]

I think I know who the Dirt-man is referring to.  :rotfl2:   Everything Renault has had a hand in design and engineering is weird, but I have to admit the knock sensor is a damn good feature. However one good feature doesn't come close to negating all the other goofy stuff on a Renix system.

[benjy_26]

My question is: Does 2.5 engine have a knock sensor as well?

[mikekaz1]

My question is: Does 2.5 engine have a knock sensor as well?

 

id imagine it does... :dunno:  the 4.0 is/was based upon the 2.5 in design. so id imagine if the 4.0 had it so would the 2.5

[cruiser54]

The factory test is to read the output on the scanner. You will see it reading 0. Rev it to 2000 RPM and see the value change to a flickering 20 or so. 

 

I had an aftermarket one on a supercharged Miata that was tied to the ECU. Came as a kit with a little readout of colored lights yo could watch from the dash showing how many degrees the timing was being retarded. This is the company that made mine.

 

http://www.jandssafeguard.com/tech.html

 

Per the factory wiring diagram, no knock sensor on the 2.5.

 

And, this is nothing exclusively weird to Renault. GM and many others used knock sensors, as did AMC on the later 258s.. 

[benjy_26]

Thanks for the info! I guess AMC skipped the knock sensor on the 2.5 thinking people wouldn't beat on them too much. Little did they know...

[HOrnbrod]

The 86 2.5L had a knock sensor on the intake manifold, p/n 33000902. Looks like it was dropped on the 87 and up engines though.........

[johnj92131]

The factory test is to read the output on the scanner. You will see it reading 0. Rev it to 2000 RPM and see the value change to a flickering 20 or so. 

 

I had an aftermarket one on a supercharged Miata that was tied to the ECU. Came as a kit with a little readout of colored lights yo could watch from the dash showing how many degrees the timing was being retarded. This is the company that made mine.

 

http://www.jandssafeguard.com/tech.html

 

Per the factory wiring diagram, no knock sensor on the 2.5.

 

And, this is nothing exclusively weird to Renault. GM and many others used knock sensors. 

 

 

J & S has been around a long time.  First heard of them in the late 1970's from an old Corvair buddy who was using one of their products on his Corvair.

[cruiser54]

The 86 2.5L had a knock sensor on the intake manifold, p/n 33000902. Looks like it was dropped on the 87 and up engines though.........

Probably the same one as used on the 258s that was located in the intake manifold. We used to tap the intake manifold with a big wrench and observe the 258s slowing down as the timing retarded. 

 

Call John at J&S if you are considering getting one. Super nice guy. 

[mikekaz1]

so correct me if I'm wrong... that J&S kit is a "piggyback" module that you put inline with the dist/coil  to modify the spark activation, dependent on the knock signal?

[cruiser54]

so correct me if I'm wrong... that J&S kit is a "piggyback" module that you put inline with the dist/coil  to modify the spark activation, dependent on the knock signal?

Yup. 

[mikekaz1]

hmm. that's actually pretty cool! could be beneficial especially with a stroker set up

[cruiser54]

hmm. that's actually pretty cool! could be beneficial especially with a stroker set up

Kept my blown Miata engine together!!!

[mikekaz1]

Kept my blown Miata engine together!!!

 

nice :thumbsup:  how much do one of those go for? didn't really notice any pricing when scrolling that site

[cruiser54]

The knock sensor set-up was already on the car and then I installed the SC. 

[Gubachoo]

I have had a hard time finding the torque value on the stud and then the sensor for the new sensor. Anyone? Maybe a photo from the service manual as I have heard quite a few different values depending on who you are. Thanks.

[Ωhm]

Knock Sensor: 89 "lbs   (10 Nm)

[Gubachoo]

On 10/29/2023 at 9:35 AM, Ωhm said:

Knock Sensor: 89 "lbs   (10 Nm)

Perfect thanks. I'm guessing the stud doesn't need any specific torque then. 

[gogmorgo]

Studs generally don’t require torquing. There are some exceptions of course, and you usually want to run the stud all the way in for maximum thread engagement, but for the most part it’s really just a through-bolt with a nut on both ends. The inside nut in this case just happens to be shaped like an engine block. But as long as the outer nut is torqued correctly it will provide adequate “bolt” tension.