Knock sensors
Turbo Mini Forums

Built my ignition controler last week, so am now thinking about how I can map it with out spending hundreds on the rolling road.
(Read as reduce rolling road time not as don't RR at all!)

If I get a knock sensor off another car, and make a circuit to detect the knocking, can I advance the ignition at a given rpm/load untill I just detect knock then back off a few degrees?

If so, where should I mount the knock sensor?

Any comments welcome!

You are unlikly to be able to knock up a simple controler for a knock sensor... they are a very simple device that needs alot of processing to make sence of the data.

You need to place the knock sensor in a position where if it detects knock then the control unit can work out which cylinder is causing the problem. So normally one between every 2 cylinders for maximum "listening".

Alex

AlexF

you could possibly do as i suggested in another thread(on this forum i htink), epoxy/weld/otherwise solidly mount a pieso diafragm to the block in the appropriate place, then hook it up to an amp and headphones(old cassete player, replace reading head with piezo) and jsut listen for knock! that way theres no need for complicated DSP stuff, you jsut use your ears! imagine ther ewil be an audiable change when the ignition is to advanced!

worth a try, piezo = £1-2 old personal stereo = free in most household id imagine and some epoxy = free in most car enthusiasts supplys. :)

Edited by evolotion on 12th Sep, 2004.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Got a plan for a knock sensor circuit already, was more interested in best mounting position on an A-series, and how much to retard the ignition by.

In the winter, I want to incorperate a knock detector into my ignition controler, but will need to write a bit of software to do that and I'm out of practice!

I think you could be right about needing two knock sensors though.
The problem with the a-series is it such a noisy engine, the rockers in the head, timing chains and drop gears could easily trigger false readings.

spose I'll just have to work it out myself. I was just wondering if the big power boys had done it already.

BTW I tested my narrow band lambda sensor circuit today, it shows up my flat spots as lean outs very well. I was suprised how stable the readings were.
I blocked up the part throttle leanout pipe, and I could see the mixture richen and it cured a flat spot at 2500 rpm.
I think I'm definatly going to go wide band soon, after reading prievious posts. But the narrow band sensor for the £2 it cost me to make is definatly a worth while tool.

Edited by Gibbo on 12th Sep, 2004.

gibbo, what kind of signal processing you useing? I did a class on signal processing at uni, and, erm, it went right over my head!! sooo much maths :(

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Knock sensor on the 'A' should be achievable, but the location / locations needs a lot of experimentation i expect...

Somet worth looking into though!

let us know how you get on mate

Team www.sheepspeed.com Racing

Yeah, will do.

This week I managed to get a trigger wheel off a 1.8 sierra (fits the mini pully spot on!), and weld it to my crankshaft pully, so hopefully I'll have time on the weekend to fit my igniton controler and get it running.


So perhaps next week I can make a start on fitting a knock sensor.


Been reading about the SAAB APC boost control system, basically from what I can gather it uses a knock sensor to operate a solinoid, that opens the waste gate if knock is detected so backs off the boost.
This all hapens in a very short time so the car will drive very near the detonation point.
I can't find working web pages detailing installing this system on another car at the moment though.
But it sounds like its only a knocksensor, "Blackbox" and a solinoid.

If anyone knows anymore about this please let me know as there's no point me re-inventing the wheel if I can achieve the same goal by fitting somthing from the scrappies!

I'll take some pics of my megajolt ignition system as I install it and post em up.

Hi Gibbo
How did you go about making up a lambda mixture sensor? I was thinking about this after reading you post the other day, does the lambda give out a set voltage to indicate lambda = 1, and then vary either way? If so I was thinking about knocking up a series of LED's using resistor voltage dividers to make the LED's light up as voltage rises/falls...

Is this along the right lines or am I talking ARSE!
Basically want to end up with something like the box with LED's in that Lumenition sell but without spending £140.

This site is the best I found.
http://www.buckeyetriumphs.org/technical/C...r/AFMonitor.htm

The circuit on there needed slight tweeking to work accuratly with my lambda sensor, and i also needed a 1Mohm resistor to ground accross the lambda output otherwise the circuit charged and all the LED's gradually lit.

Its basically a high impedance voltmeter, nothing special but it must be set accuratly to be of any use, so a good voltmeter or a scope is needed when building.

His build quality is a bit lacking though!

Edited by Gibbo on 16th Sep, 2004.

Even MiniMark would do better....

blimy!

AlexF

Why did that pic make me laugh even though I seen it before?

Perhaps he would have been better off using a mig instead of a soldering iron, cos he done a good job fitting the nut for the lambda. Then it all goes wrong. lol

Build it on vero board, FFS don't do what he did cos fault finding would consist of binning it and starting again!

i might dig out my electronics gear and have a bash. got a few of the 3914 chips kicking about at home. good for battery monitors and themometers.

Yeah I am planning on having a go as well, had a quick peek in the RS book and all the bits only total up to about a tenner.
When I was at school doing electronics AS level we used things called breadboards that were quite neat for connecting things up, might try and get one of those.....

yeah ive still got mine. really easy to use for testing stuff out. Hmm now where is it?!

Hi Tom! I am selling a complete narrowband lambda kit with brand new Bosch lambda sensor + welding bung for 100pounds+postage.
Mail me if you are interested.

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

Gibbo,
don't suppose you have a piccy of the sierra trigger wheel?
How big is it? (diameter and width)

Rich

Here for the craic..

Supercharged Arden powered

It's around 120mm diameter and about 10mm thick.

I can post a pic of my trigger wheel fitted to the pulley. If someone can tell me how to do it! lol

Harry,
Cheers for the offer but quite fancy having a go at building one myself.
Cheers

Hello gibbo, first of all, thank you for megasquirt.(i'am assembling my megasquirt since a week).

I'am an internal combustion engine technicien and I'm a bit experienced with knocking. It's another kind of work that injection.
In fact, you have to detecte knock but not valves. Because sensor can detecte a valve which is closing a bit quickly and so "jumping". This phenomena made vibration on your head and sensor thinks it's knocking. To solve this problem you have to make a window during which the sensor is avaible and the rest of the time the sensor doesn't work. It's a bit hard because If you change the fuel of your car (gasoline->methanol for exemple) you will to change the window. The window is approximately (15 degrees before Top Dead End and 10 degrees after Top Dead End). If you want more explaintion send me a mail at oob41@hotmail.com.

The advance value are not the maximale but the optimale. But sometimes knocking is before optimale advance so you need a knocking sensor to try to be the nearest is possible from the advance of maximum torque. Sorry for my english, I'm "en lendemain de cuite".

French turbocharged 998cc

The ECU's I’ve dealt with to date have what’s known as a Knock Noise Lookup Table. This table is use to determine the engines back ground noise levels at given RPM’s and if the ECU sees an input from the Knock sensor above the given look up tables value it classes the noise as Knock and reacts to it by retarding the ignition and adding small quantities of fuel to cool things off.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Cheers for the info guys!

My rapid progress is coming to a halt! due to other commitments, so its gonna be a Winter project by the looks of things.

If I do suceed in geting some usefull results a few months down the line, from a knock sensor on the A-series then I share how I've done it with you!

Hi, I visited LNYX Racing in northamtonshire about 2 weeks ago, he sells a polestar ecu that i was enquiring about and from what he explained within the next month they should have a saleable knock sensor addition to the ecu. I am unsure how reliable this polestar system (has anyone on here used it) is but I beleive it has been tested in a few miglias. Price wise he was talking about £500 for ecu and loom.

If you have not already been on his site its worth a visit just to look at his flywheel kit, it a bit unusual. http://www.lynxae.co.uk/

Jase

SRE sell polestar stuff too

I spoke to Neil Slark about it
sounds interesting