BMW m50tu megasquirt 2 misfire

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mike.demirjian
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BMW m50tu megasquirt 2 misfire

Post by mike.demirjian »

Hello guys, so after installing the megasquirt 2 and getting a base tune, the car is perfectly idling and driving on high rpms. the only problem i am facing is that i get a misfire , pretty much sounds like a rev limiter when i'm on part throttle and 2600-3000rpm.

Here is my datalog file, please give it a look. will be thankful for suggestions.
october misfire.msl
misfiring on 3000rpm
(962.34 KiB) Downloaded 27 times
prof315
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Re: BMW m50tu megasquirt 2 misfire

Post by prof315 »

You are probably losing sync. Either sensor polarity is inverted or ( if you use a VR crank sensor with a v3.57 mainboard) you need a 10K resistor inline on VR +. Pretty common when using a high tooth count missing tooth wheel.
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mike.demirjian
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Re: BMW m50tu megasquirt 2 misfire

Post by mike.demirjian »

Thank you for your reply prof315. Polarity is definitely correct since i have checked it. I will try adding a 10k resistor on VR+ and see how it goes.
billr
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Re: BMW m50tu megasquirt 2 misfire

Post by billr »

There is no sync loss in that log, though. I wouldn't fuss with the CKP circuit just yet. There is a lot of variation in the battery voltage, I'm suspecting a problem with the power/ground wiring.
mike.demirjian
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Re: BMW m50tu megasquirt 2 misfire

Post by mike.demirjian »

Thats what i have noticed too. Voltage is dropping to around 11.2v when this misfire occurs. I will check both 12v and ground circuits.
mike.demirjian
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Posts: 10
Joined: Sat Jul 29, 2017 1:50 am

Re: BMW m50tu megasquirt 2 misfire

Post by mike.demirjian »

i have corrected the battery voltage and it is pretty stable now, but i am still facing the same problem on 2600-3500 rpm. i have made a tooth logging log, and it doesn't seem to be losing sync at any point. could you please give it a look? thank you in advance.
monday test drive.msl
Test drive logging
(655.73 KiB) Downloaded 29 times
tooth logger.csv
tooth logger that i have made during the misfire as well
(86.92 KiB) Downloaded 23 times
prof315
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Re: BMW m50tu megasquirt 2 misfire

Post by prof315 »

Looking at the log my money is on a rich misfire. Get rid of the narrowband O2 sensors and put a wideband in or you're playing blind mans bluff.
Linfert Performance/321 Motorsports
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mike.demirjian
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Re: BMW m50tu megasquirt 2 misfire

Post by mike.demirjian »

I solved the problem, just like you said it was running rich, so i edited the ve table and lowered the fuel quantity and it worked like a charm. Thank you both for your support.
prof315
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Re: BMW m50tu megasquirt 2 misfire

Post by prof315 »

So now get off of your wallet and get a wideband. A Spartan 2 by 14point7 is only $125 for a controller and sensor.
Linfert Performance/321 Motorsports
SCCA 2019 SM National Champion Crew Chief
SCCA 2023 FP National Champion Tuner/electrical engineer
100s of MS systems built installed and tuned
Support the developers!
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