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Old 08-15-2019, 05:52 PM   #1
Mmk64
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Another misfire thread. Out of ideas!

Hi all, I've been scouring the internet trying to figure out my misfire problem on my 05 325ci manual with 150,000 miles. Initially I was having lean codes and cylinder 1 misfire only. Car was sluggish, found some vacuum leaks and fixed but issue persisted. Changed both precat o2 sensors and fuel filter, car is much more responsive but still misfiring but under higher load. 5k plus with full throttle, I hear a sputtering sound and cylinder 1 misfires. No more lean codes.

Fuel injector on cylinder 1 was replaced, coil/spark plugs replaced on cylinder 1 and 2. Still same sputter and misfire. Idle is fine.

I decided to redline at neutral today, sputter sound with misfire on a completely new cylinder (2). Vcg has been replaced not long ago, vanos too.

When fuel filter was removed, black liquid was inside. It was the original filter. Maybe increases likelihood of cylinder 2 injector also being bad? Seems weird to have 2 injectors go bad

I'm at a loss. Any help would be much appreciated!

Last edited by Mmk64; 08-15-2019 at 06:07 PM.
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Old 08-15-2019, 10:26 PM   #2
ralf
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Check your spark plugs and verify if they are the right model and temperature also check there is not any hairline cracks on the porcelain indicating arc discharge, in doubt better replace them all with original or NGK standard spark plugs, don’t go with any other.
While you’re on that check compression in all your cylinders specially #1 and compare numbers between them.
Move your coil to another cylinder and check codes,
Move your fuel injector to another cylinder and check codes
If misfire is still on cyl 1 could mean that you have a faulty harness connection, faulty wire coil or harness but since you are experimenting the failure under high engine load I suspect of spark plugs
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Old 08-15-2019, 10:45 PM   #3
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Misfires usually trigger trouble codes, so read those. If the SES light is on then also read the freezeframe data.
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Old Yesterday, 11:35 AM   #4
Mmk64
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Thanks for the suggestions, I will add to my list. The only code I get is misfire when the check engine light goes on.

I was thinking of temporarily unplugging the MAF and see what happens. If issue is solved by this extra rich setting without the MAF, Would that point towards fuel injector being an issue rather than coils and sparkplugs?
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Old Yesterday, 11:36 AM   #5
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How do you know you still don't have a vacuum leak somewhere? Have you done a smoke test?
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Old Yesterday, 11:44 AM   #6
Mmk64
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Quote:
Originally Posted by Spannerhead View Post
How do you know you still don't have a vacuum leak somewhere? Have you done a smoke test?
Yes, smoke test was negative. Also, no more lean codes after fixing leaks and changing O2 sensors, just misfire
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Old Yesterday, 05:45 PM   #7
Mmk64
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So I exchanged my MAF with a used one, no difference. Unplugged it completely, can redline without a misfire but still makes a sputtering sound and hesitates near redline
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Old Today, 08:28 AM   #8
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What brand are the new oxygen sensors? Bosch?

Unplugging the MAF forces the DME to rely upon the pre-cat sensors’ data streams to adjust the fuel/air mixture. It also forces the DME to use an overly rich fuel/air mixture. Why? Unplugging the MAF puts the DME into the “open loop” mode.
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Old Today, 08:31 AM   #9
Mmk64
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Yes Bosch, brand new. Gas mileage and acceleration greatly improved immediately after
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