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Help !!! need to diagnose my 09 M8 computer. Vail area.

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hawktoy85

Member
Mar 5, 2013
134
18
18
I have an 09 M8 with turbo that after rebuilding the motor last year started Blinking ECU code 21 " Knock sensor failure". Traced all the wires, can't find any issues. Changed the knock sensor, Didn't help. Wiring harness is over $400 so need to do more diagnosing before replacing.

Looking to maybe put my computer into someone elses sled and see if it does the same thing. Mine, within 10 seconds will start flashing ECU 21. So would be pretty quick to check.

I live in Avon, co and will to travel to summit county or glenwood?

If you can help in anyway call, PM or post here.

Thanks

Jake
nine 70-36one-5777
 
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arctic2009

Well-known member
Nov 19, 2009
1,864
670
113
Minnesota
I have an 09 M8 with turbo that after rebuilding the motor last year started Blinking ECU code 21 " Knock sensor failure". Traced all the wires, can't find any issues. Changed the knock sensor, Didn't help. Wiring harness is over $400 so need to do more diagnosing before replacing.

Looking to maybe put my computer into someone elses sled and see if it does the same thing. Mine, within 10 seconds will start flashing ECU 21. So would be pretty quick to check.

I live in Avon, co and will to travel to summit county or glenwood?

If you can help in anyway call, PM or post here.

Thanks

Jake
nine 70-36one-5777

Have you tried putting some fresh gas in it??
 
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diggerdown

Well-known member
Apr 25, 2004
3,452
677
113
Deer Park Wi.
You sure everything is torqued to proper specs? I doubt it is the wire harness, maybe the connecter plug. Most issues are fuel or head bolt torque.
 
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hawktoy85

Member
Mar 5, 2013
134
18
18
I have checked torque on knock sensor, but not on cylinders. Guess I'll check that. I have gone over all the wire and related plugs and can't find any problem. The code pops up as soon as the computer boots up. Its not after a certain rpm or anything.

And yes I have tried new gas. I run AV gas now with my turbo. But have also run Straight VP110.
 
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fast8seccamaro

Well-known member
Oct 22, 2010
394
157
43
Thorsby Alberta
They can throw codes once in a while with no detonation but if your light is always wrong there has to be something wrong with the harness, torque or something. Make a small threaded bracket for the detonation sensor and mount it solid to the handle bar upright or something solid. It won't flash but your tune has to be good! Even if it works at idle it might give you some insight
 
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hawktoy85

Member
Mar 5, 2013
134
18
18
I did a lot of diagnosis last season. I tried take knock sensor out grounding it to the chassis and running the sled and same result. I am pretty sure it is either the harness or the computer. That is why I am looking to find a sled I can put my computer in and just see if it's the computer or not.
 
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kingkat1150

Well-known member
Jan 27, 2010
161
98
28
belgrade mt
Knock sensor

I had the same issue with a 2011 m8 last year and what I found was a broken wire rite at the connector on the main harness going to the knock sensor. The wire looked fine but it was broken inside the wire sheath and was only found by doing a continuity test. What was strange was the light would flash on one start and stay on solid on another start. works fine now.
 
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hawktoy85

Member
Mar 5, 2013
134
18
18
I get good continuity between plug and computer. Thinking must be somewhere else casing short and "ecu 21" is just the result of the short. I am going to start working on it again to get ready for winter and really need to find someone with my same sled to just make sure it's not my computer.
 
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hawktoy85

Member
Mar 5, 2013
134
18
18
Lets try this again. Please read my first post. I really need to figure this thing out.
 

backcountryislife

Well-known member
Lifetime Membership
Nov 26, 2007
10,893
7,413
113
Dumont/Breckenridge, CO
Post up in the local section man... tons of 07-09 M8's here.

Another thing that you MAY not have thought about... (something that happens on silber poo turbos a LOT, but never seen it on a cat) is anything on the motor hitting the chassis or turbo assy... any contact can be read as "knock" by the sensor. Just something to consider.

Got a buddy with an 08 in the Ho here in clear creek that I could likely talk into trying, but he's on an oil boat for another 3 weeks.
 
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hawktoy85

Member
Mar 5, 2013
134
18
18
I have checked on model numbers and computer and wiring harness are specific to 09 only. So I think I need to find an 09 M8. I am hoping someone will reach out and help out.
 
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diggerdown

Well-known member
Apr 25, 2004
3,452
677
113
Deer Park Wi.
You know you might want to tell people where you are from so locals will chime in. Does no good to have someone two states away offering to let you plug into his sled!
 

m8magicandmystery

Well-known member
Lifetime Membership
Jan 20, 2008
7,786
3,724
113
Yukon
for the second it takes try bypassing your fuel controller back to stock for checking to see if it still does it..i had code 21 and i bypassed my purelogic controller and code went out so i put new controller on and all is fine...for some reason a wiring/faulty fuel controller did the 21 code.
 

Rixster

Well-known member
Premium Member
Oct 20, 2005
3,781
651
113
47
Springville, UT
Had this exact same problem with a friends 07 m8 after a rebuild last year. Finally decided that during the rebuild the sensor was placed in a magnetic bolt/nut bowl and that screwed up the sensor.
 
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