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Old 09-04-2016, 02:24 PM   #1
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Default Bosch 3 wire Knock MS3



Ordered the wrong Bosch Knock sensor off amazon and I am trying to make work. Part number Bosch 0261231038. It is a 3 wire Audi sensor with a built in tail.

I have a Rev built MS3. I removed the intake brace and I am using the M10-1.25 hole it mounted in. I stepped it down to m8-1.25 carefully with a heli-coil and it actually worked well. I am using shielded belden 8451 to run a line direct from the Sensor to the MS3.
Bosch Pin 1 sig + to MS3 DB33.
Bosch Pin 2 sig - to MS3 DB Pin 3 analog sensor ground.
Bosch Pin 3 Shield to drain wire and ground to chassis near where computer is to protect the whole run?

I plan on soldering the wire direct to the sensor pins.

Last edited by farpolemiddle; 09-05-2016 at 02:01 AM. Reason: Mixed up pins
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Old 09-05-2016, 01:47 AM   #2
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So the plan is the same but I am going to try and use the rest of the MAF sensor wiring from the stock harness that I did not use need after the GM IAT conversion since it is shielded from the factory. I should be able to run

Pin 1 on the bosh across the engine bay to the RED shielded wire.

Pin 2 sensor ground to the BLACK/BLUE STRIPE to ECU ground.

Pin 3 sensor hooked to the drain wire and grounded to chassis near where I tap into the MAF wiring?


The 12V source on the MAF harness will not be needed.

At the computer side all I should have to do is de-pin both 20s or jump them to RED/DB33 knock input and BLACK/B to DB3?

Does this sound right? I really did try and search this stuff.



I am also going to try the same thing with my Flex Fuel sensor but I will be using factory o2 wiring sine I did not use any of it for the wideband.

Vcc Flex 12V to 12V on o2 harness
Flex Sensor Ground to Ecu BLACK/LG 2C
V out Flex Sensor Signial to RED/L 2N
Shield on jumper to 4th ground or chassis near by?

Jump RED 2N to MS3 to DB26
Jump BLACK/LG2C to MS3 DB3?

or just run new lines like I originally planned and leave the factory harness alone?

Can I share grounds knock and flex on MS3 DB3 or should I ground one of them to DB21?

Last edited by farpolemiddle; 09-05-2016 at 02:07 AM. Reason: Mixed up pins
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Old 09-05-2016, 08:50 AM   #3
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I don't know about the knock sensor but I wired my flex in like you are planning. For whatever reason I get a varying signal like noise. The flex signal wire is tied into the factory o2 signal wire which is shielded. The ground wire for the o2 does not go to the engine on my car but instead to chassis ground. I'm going to try and put that to engine ground one of these days and see if it makes a difference. Something tells me the flex sensor is better off grounded to the engine.
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Old 09-05-2016, 01:17 PM   #4
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Quote:
Originally Posted by hector View Post
I don't know about the knock sensor but I wired my flex in like you are planning. For whatever reason I get a varying signal like noise. The flex signal wire is tied into the factory o2 signal wire which is shielded. The ground wire for the o2 does not go to the engine on my car but instead to chassis ground. I'm going to try and put that to engine ground one of these days and see if it makes a difference. Something tells me the flex sensor is better off grounded to the engine.
See this is what I am trying to avoid. If I am going to go through the trouble of using the factory harness I don't want noise. I am starting to think it is a better idea to just run a dedicated signal wire with shield and ground the shield/drain wire on the engine or chassis. I will still use the O2 power. I am confused because all the reading I do on sensors mentions ground to ECU.

Interesting that this AEM instruction looks like the Flex sensor I am installing and they specifically label it as
Pin 1 Vcc-Battery 12V
Pin 2 GRN-Battery Ground
Pin 3 Vout- Sensor Output

http://aemelectronics.com/files/inst...nsor%20Kit.pdf

So you are probably right. Just ground the Flex to the engine/chassis right there and use just the 12V source from the o2. Then I could either run a new shielded wire with the drain/shield wire grounded on one side and the shield signal hooked up to the MS3 or do the same thing with the factory wiring RED 2N de-pinned and hooked up the MS3.


I am pretty sure the knock sensor has to ground to the ecu. It is basically a mic.

Last edited by farpolemiddle; 09-05-2016 at 09:42 PM.
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Old 09-05-2016, 01:33 PM   #5
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Sourced from

Megasquirt Support Forum (MSEXTRA) ? Question about Crank/Cam VR Sensor Wiring, Shields, and GND (View topic)
DaveEFI-
"With all sensors the rule of thumb is to run both 'hot' and ground right the way back to the DB37 connector, and only connect the grounds together there - and to a pin or pins you dedicate to sensor grounds only. The power grounds go to different ground pins. (It doesn't much matter what ground pins are used - just keep sensor and power grounds separate within the connector. They are then commoned inside MS.
The VR cable screen isn't carrying any current since it is only connected at one end, so it doesn't much matter where it is grounded to at the DB 37."


In regards to 3 wire knock sensor

Megasquirt Support Forum (MSEXTRA) ? How to test knock sensor circuit? (View topic)

Has a pretty good diagram showing a dedicated shield ground to a MS. Is their any reason I could not use DB21 device ground on the MS3 from now on as a dedicated shield ground? Reverant?

Last edited by farpolemiddle; 09-05-2016 at 09:43 PM.
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Old 09-05-2016, 03:26 PM   #6
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Both sig- and shield ground to pin 3.
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Old 09-05-2016, 08:36 PM   #7
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Quote:
Originally Posted by Reverant View Post
Both sig- and shield ground to pin 3.
Does the same go for the flex fuel if I run a new dedicated wire as well? Shield and ground both to pin 3?

Last edited by farpolemiddle; 09-05-2016 at 09:44 PM.
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Old 09-11-2016, 11:52 PM   #8
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Seams to work well. I plan to try and make it useful later down the road with a set cans on a dyno but I'm not going to count on it actually being useful.

Last edited by farpolemiddle; 09-12-2016 at 02:40 PM.
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Old 09-12-2016, 06:46 AM   #9
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Quote:
Originally Posted by farpolemiddle View Post
Does the same go for the flex fuel if I run a new dedicated wire as well? Shield and ground both to pin 3?
if you plan to run a shielded wire for that, yes.
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Old 09-12-2016, 02:40 PM   #10
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Quote:
Originally Posted by Braineack View Post
if you plan to run a shielded wire for that, yes.

I installed the flex using the existing O2 power , ground, and signal. I de-pinned the signal and ran it into the flex on MS db32. It is not working. My fuel temp and ethanol read zero. I went into CEL settings and had it check FLEX and it came on as a "Flex fault" so I am stumped. I checked my wire again and seems right. I even ran a jumper outside the car straight from sensor to the MS. Only thing I can think of is perhaps bad sensor but my multimeter doesn't do freq.

Last edited by farpolemiddle; 09-12-2016 at 08:20 PM.
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Old 09-14-2016, 06:49 AM   #11
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Can't remember where I read it but there was a rash of bad sensors out there. Did you get yours from GM?
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Old 09-14-2016, 04:43 PM   #12
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Quote:
Originally Posted by hector View Post
Can't remember where I read it but there was a rash of bad sensors out there. Did you get yours from GM?

no. It is from Amazon. I need to test it but my multimeter does not have freq
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Old 09-16-2016, 06:46 AM   #13
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https://www.miataturbo.net/megasquir...h-86905/page2/

You probably already read that thread but that is an example of two people that had sensors not read in the correct range. Can't remember where I read the DOA sensors on. Might have been that thread Aidan started with the link to the mr2 site? In that same thread you have a link to a GM dealer that sells the sensors. Get one from them.
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Old 11-11-2016, 09:37 PM   #14
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Just closer on this even though it drifted from my knock sensor. The ******* flex sensor was bad from the start. I ordered the bigger coni sensor and it worked right away. 9%. I spent hours ******* with that other one....
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