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      11-12-2019, 10:50 PM   #1
Blaibhen
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Issue after changing spark plugs

I have a 2015 bmw M4 with 42k miles, drop in filters primary/secondary cat delete, Currently running bootmod3 stage 2 (agg) tune with 8k on tune. Last night I changed my spark plugs to NGK 97506, i gapped them all to .020 and torqued to 18ft/lbs, I put everything back together and started/revved the car and it sounded fine at that point I was tired so I left it in the garage cause it was late and didn't feel like test driving it. The next day i went for a test drive and noticed that it drives around fine when cruising, but when giving it full throttle it sounds very hesitant and is sluggish. No check engine light and it also revs normal when in neutral. At idle i notice a very small hiccup every couple of seconds. I than reflashed my tune just to see what happened, no change. I also checked my boost numbers on the dashboard tool on bootmod3 and I hit 22-24ish PSI before letting off because I don't want to break anything (the car seems very sketchy at full throttle) so I know it isn't a leaking charge pipe because its building boost. Next step I took the plugs out a re-gapped them to .024 (slightly closer to stock spec) and had the same issue with no change. The next part is where I was very confused... I put the stock plugs back in and still have the same issue, I tried flashing to stock tune and the car ran even worse... Any one have any idea of what it could be? I'm assuming I MUST have missed something during the process, I've looked it over countless times with no luck, and no CEL also makes it very difficult to troubleshoot, ill post a link to a video so you can see how it runs. Thanks in advance!!

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      11-13-2019, 08:19 AM   #2
andrei.m4
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i have same sound in 3500-4000 rpm with second and thirt gear, with bm3 8.7version no problems and after i installed 9.0 new version this problem apeared. I never tested again previews version. Also on fb bm3 group a lot of people talking about this problem.
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      11-14-2019, 01:02 PM   #3
wangboy925
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Silly question but did you connect everything? It has happened to me in the past to forget to reconnect an electrical connector.
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      11-14-2019, 01:26 PM   #4
Blaibhen
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Quote:
Originally Posted by wangboy925 View Post
Silly question but did you connect everything? It has happened to me in the past to forget to reconnect an electrical connector.
I looked over everything 3+ times and can not find anything disconnected. Its crazy that no one has experienced this issue, no CEL, car just runs absolutely terrible.
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      11-18-2019, 06:48 PM   #5
blockdoc
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Quote:
Originally Posted by Blaibhen View Post
I looked over everything 3+ times and can not find anything disconnected. Its crazy that no one has experienced this issue, no CEL, car just runs absolutely terrible.
Have you verified that you didn't crack one of the plugs? It is VERy easy to do as these are very brittle. Even overtorquing just a hair can cause the insulation to crack, leading poor spark in that cylinder. All it takes is a hairline crack which is very easy to miss if you are not looking for it. Ran into this problem on MY car a year or so ago

Do you have e access to ISTA? You might be having an issue which is enough to cause power problem, but not enough to trigger a full CEL.


Just a thought

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      11-19-2019, 10:14 AM   #6
Alan l.
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Something def. sound wrong. I would remove all of the plugs to visually check them.
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      11-19-2019, 11:05 AM   #7
coldfish
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You have primary cat delete, so i will check if your O2 sensor is still good...
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