Knock/Timing Retard voltage.

[Cej2525]

I have searched for a few hours now with no definative answer or info so I pose a few questions.

1) What are the voltage or ohm range seen at low levels of knock and timing retard?
I understand we gauge knock by observing timing retard. That being said the knock sensor it self has to be transmitting some form of data.

2) Also I understand no knock is acceptable. But when it does what do you veterans consider low,mild and wild. Im really just looking to kind of scale things out.

My reasoning behind this is I want to make my own knock warning system and maybe even create my own limp mode or fail safe. Any info or advice is welcome.

 

[RmvBfrFlght]

The knock sensor is a microphone. Similar to the one a DJ uses. That signal is A/C voltage/current to the knock filter (talking stock '86/'87 TB).

The knock filter is known as an acoustic filter. It is really the brains of the operation. It listens to the signal from the knock sensor/microphone, and decides whether the "engine noise" sounds like knock is occurring.

If so, it uses a digital signal in the form of a low going pulse to inform the ECM. The ECM then reacts upon the duration of the low going signal by reducing/retarding the spark advance (and sometimes the level of boost).

In general it works rather well. The problem is that other noises can also sound like maybe knock is occurring. Tire spin, bad accessory bearing, exhaust rattle, can contribute to false knock.

As far as how much is OK, none when it is real knock and in boost.

RemoveBeforeFlight

 

[Cej2525]

Thanks for the response RmvBfrFlight. So knowinb that the knock sensor is recieved as some form of data stream like rs232 or 485 gues I need to look at finding the overall voltage range the ecu will send out to retard timing under a knock situatuion. Then I may be able to use that with a series of op amps or eproms to run a notification/limp scenario.

 

[RmvBfrFlght]

It is even simpler then that. The knock sensor is a microphone, and the signal from it is an analog representation of what it "hears." You can literally connect a set of headphones to it (w/a little amplification) and also listen in on the sounds of the engine.

The output of the knock filter is digital. For an alert device, just look for the output voltage of the filter to fall below 2 to 5 volts. A 9 volt signal is no knock. The filter pulls that voltage low.

RemoveBeforeFlight

 

[Cej2525]

So to make sure i got this right before I start soldering me up a circuit.

If 9v is no knock and you are saying a warning system should sound off between 2-5v is it safe to say that 0v is the most severe knock that the sensor can read? If so then that is the exact information I was looking for. i understand that a curtain amount of noise is present and the sensor/ecu determines what is actually knock. The main issue here is it's impossible to acquire this data without spending a lot of time and money changing head gaskets. You sound like you have a pretty good knowledge of this circuit and i greatly appreciate your inf so far. In your opinion what would be a good low and high end range? the 2-5v you spoke of. 5v being light and 2v being severe. My plan is to have a single signal light at light knock only pulling say up to -2 degrees of timing then an audible alarm up to about 5-6 then possibly dumping the boost at higher levels. thanks in advance for all opinions including RmvBfrFlight.

 

[blackdeathtrap]

here what i think would be a simpler way of doing this get a casper knock gauge splice into you light at you diferent severyti level to do you different functions

 

[RmvBfrFlght]

The signal from the knock sensor going low indicates knock is being heard. The duration of the signal defines how much knock. IIRC, the low going signal is of multiples of 1 milli-second in duration. So if the knock is severe it may go low for 5 or 10 milli-seconds. Light knock may be 1 milli-second.

RemoveBeforeFlight

 

[Cej2525]

Understood RmvBfrFlight,I honestly do not have the electrical expertise needed to make a circuit needed to read those perameters. I was hoping to intersept a wider analog voltage range to monitor knock. Maybe I need to look at intercepting the votage sent to retard timing AFTER the ecu does it's voodoo magic with processing knock. Would that signal possibly be sent to the ignition module?

 

[Cej2525]

here what i think would be a simpler way of doing this get a casper knock gauge splice into you light at you diferent severyti level to do you different functions

You have a very valid point and that would work. But I wanted to have something a little different and possibly adjustable parameters for each warning and function.

 

[pacecarta]

http://www.gnttype.org/techarea/projects/projectspage.html

see the articles on building your own kr meter
old but none the less it was there all along , need to search some times

what you do with the output is limited only by your imagination

 

[Cej2525]

Thanks for posting the link man. I will study it well. FYI between TB.com,Vortexbuick,gnttype and multiple other vendors I have printed off three packs of printer paper worth of research. Enough to fill up 4 three ring binders. I understand the neverending common questions being asked but I feel this one was a bit more specific. Once again though thanks for the link as it is more info and I like me some information.

 

[RmvBfrFlght]

Understood RmvBfrFlight,I honestly do not have the electrical expertise needed to make a circuit needed to read those perameters. I was hoping to intersept a wider analog voltage range to monitor knock. Maybe I need to look at intercepting the votage sent to retard timing AFTER the ecu does it's voodoo magic with processing knock. Would that signal possibly be sent to the ignition module?

The link that Paul provided is a pulse stretching circuit. Which is all that is required for a knock alert device. Basically it makes the low going knock detected pulse longer.

The ECM changes the spark advance in response to knock. This is done in the ECM and affects the EST signal to the ICM. The EST signal controls coil dwell and when to fire the coil(s). The EST goes high (+5V) to start the coil dwell, then goes low (0V) to fire that coil.

The ECM moves the rising and falling edges relative to the incoming crank reference pulse to change the dwell and spark advance.

RemoveBeforeFlight

 

[Cej2525]

With all the information you guys have provided me with I think I have a good starting point to begin constructing a curcuit. I am currently offshore and work in the robotics field. So maybe I can get a few of these electrical engineers to lend some expertise. In your opinion is what I am proposing to build be something that the Turbo Six community would be interested in? I want to construct a small device that will have 3-5 12v outputs that will be triggered at different knock of increasing severity. These outputs could be used to trigger lights,buzzers or anything else you want. The levels that each trigger trips could be set by the installer or by me. So what ya think?