any advice or opinions from any other tuners would be appreciated.

 

My knock link was setup on almost max sensitivity from the off on my 2L and the same for the 2.5L - both would run with single green light on as normal (even when engine near idle), couple of green on boost and the odd orange flash when really thrashing it/during gear change. I also have det cans which I sometimes monitor and my mapper (Bob) has an even better setup with an electrical amplifier on det cans...def def def no det!. My sensor fitting location is the same as in pic, det cans plumbed to the inlet manifold.

 

The points are all valid, including mine. Just because no-one else does it that way, does not mean it is wrong - effectively what you are saying is that anyone who does something new is wrong.

I was never going to replace the o-e sensor with the knocklink one, but splice the two together. This will work fine, as the second wire is an earth on the knocklink, and the two signal wires are the same. Essentially all knock sensors work off of the same frequency. The bolt hole, although only 3" away is not above a cylinder, so will not give as accurate a reading and could potentially pick up other block vibrations.

The Labour time difference for me to lift the manifold or not to fit the sensor is not a massive difference and you were not overcharged.

 

Why lift the manifold tho.... i have removed my OEm knock sensor many times on my old classic in about 5 mins once the intercooler is removed. No need at all to remove the inlet manifold. As has been mentioned before, the subaru maintenance manuals show how to get the knock sensor out without taking the inlet off.....

Also a few people have taken the bolt out that secures the OEM knock sensor and replaced it with a longer item so the knocklink bosch sensor can be bolted directly on top of the OEM one.

Tony.

 

The manifold was removed to ensure that the sensor was located correctly and that the block was still clean, as I said time wise it is not much different for us to do.

If the knock link is there purely as an visual aid or indicator of a frequency being detected, then fair enough mount it in the highly position. The only other point with the higher position is that it is mounted on a water pipe bracket, so could pick up vibrations from there too. We were really only happy to fit it in the original position as we knew this would be most accurate. As you know true engine knock causes major damage if not remedied quickly, so the o-e position would pick it up first.

Although not necessarily wrong, to mount it on top of the o-e sensor is not going to give you much of a reading.

 

Can i ask why.... if it is bolted properly why can the frequency transmitted from the block to the oem sensor not be transmitted to the sensor above. It's bolted by the same bolt. What happens to the frequency/noise.... just disappears?

I'd much rather do the above than splice the knock display into the OEM sensor.... as you say det can kill an engine very quick, why mess with the ecu's ability to control this by adding into the knock circuit.

Tony.

 

I am not saying it is wrong, but the frequency of knock is quite specific, so any changes, such as position etc will have an effect on the reading of the sensor.

We modify cars on a daily basis, not just japanese cars, and if all modifications and wiring are carried out correctly there are no problems. We have to think of the customer in the long term. We would not want a customers car back because of a problem with the knock sensor and the engine has been damaged, so we have to ensure everything is done to the standards that we are happy with.

 

If by saying splicing the two knock sensors together you are meaning electrically splicing, ie: Y joining the two sensors. Then i would be very reluctant to do this.

I'm making a few assumtions here but my background is in Live audio so i know a few things about microphones (which a knock sensor basically is)

Y joining two sensors (Mics) will effect the impedance seen on the knock sensor circuit to the ECU and effectivley throw off the carefully calibrated circuit by altering the gain of the signal to the ECU.

This is not a problem when you have control of the gain but the ECU's gain will be fixed as it was only ever designed to see one sensor at a time, so with two sensors it could be one of two scenarios happening neither good.
One it could be seing less voltage and not triggering the knock control so not pulling any timing during a knock event.
Two seeing too much voltage and so pulling timing all the time due to background noise, leaving you with a flat nasty to drive car.

Personally i would just stick with two sensors, one to the the ECU and one to the Knock link. Tried and tested.

BTW if mappers are quite easily hearing det with cans bolted to the inlet manifolds of cars then i dont think that a few inches from the OEM position on the block will make much of a difference.
My knock link has its sensor in the other bolt hole as reccomended and tallyed up with Bob's det cans everytime, so no need to worry about putting it there.

Dan.

 

No, It was never intended to use two sensors, as what you say is correct. What we were going to do was to have the ECU and knocklink off the same sensor, which as they are both capable of detecting the required frequency range, mean't that it would recognise the correct frequency.

Where I think the confusion is arising is from the fact that the knock link sensor and det cans will pick up signals from any position on the block/inlet, in the o-e position it will pick up the exact frequency that the ECU recognises at the correct time in the engine stroke, i.e just before and after combustion. Perhaps we were trying to be too exact in the positioning of the sensor, but surely that cannot be seen as a bad thing on our part.

 

Splitting the signal from one mic across two inputs of two devices passivley will still give you an approximate 3db drop in level from the mic device. Opposed to the level of it just being plugged into one.
With a 3db drop in level from the knock sensor i would say you are in option one territoiry above.

Nothing wrong with trying to be really precise, just some bloke once said
if it aint broke dont fix it

I cant see any reason why piggybacking the sensors won't work as the bosch knock sensor has a metal core straight though it top to bottom so you will still have a metal to metal contact through to the second sensor.

The only way to tell for sure would be to get them both on a scope and check the outputs from each with a reference input signal.
(cue man with large hammer)

 

True, but I think we are moving away from the initial discussion. I don't consider piggybacking as being a better option than splicing the two together. The knocklink is only receiving the signal, not drawing current from it etc, so I see no real problem.

Where engines are concerned, if the crank is rotating a 6000rpm, I would like the knock sensor to pick up any det straight away, and delay due to a piggyback sensor or not in an o-e position the time delay could be critical.
As I said before, the knock link is really just a visual guide, and putting it on the higher position will suffice - we just guilty of trying to do things as well as is possible - not just a make do situation.

 

Kentperformance

Sorry to be a pain but when my mapper noticed my knocklink was spliced into the OEM sensor wire he did mention that this had the possibility of giving misleading information from the OEM knock sensor to the ECU.

I think I mentioned this post in 29.

Shaun

 

But craig, by splicing the knock link into the original knock sensor setup, you do run a high risk of reducing its effectivness. That was my worry from the start, especially when that is the sensor that feeds the info to the ecu.

I would like to add that I was certainly not overcharged, and I appreciate your point of view on this craig. But, I didn't 'mis-quote' you!

 

Originally posted by Kentperformance

Sorry it dosent work like that, as the knocklink is electrically connected it will have an effect on the signal chain unless the input to the knock link has a rediculously high impedance (say 10M Ohms, like a multimeter).

As it's designed to just see one microphone (knock sensor) in normal operation, this is very unlikley.