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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Persistent Misfire E90 330xi N52



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      02-14-2018, 04:36 PM   #1
HeyYoVio
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Persistent Misfire E90 330xi N52

I'm having issues diagnosing a persistent misfire. I'll give you some backstory and what's been done so far. Issue started with a misfire with fuel cut on cylinder #6, for which I was able to diagnose as a leaking fuel injector. I replaced all six injectors and that resolved the original problem. A couple days later I had a misfire on another cylinder, checked codes, looked for injector leaks, etc. Swapped the ignition coil to cylinder one and the misfire moved with the coil. This is where the real issue started.

So far, I've replaced all six coils and plugs (all factory parts) and the misfire still persists. It's only noticeable at idle and in the lower RPM range up to about 2500-3k; anything past 3k and the engine runs smoothly with no noticeable loss of power.

Just so I know I'm not forgetting anything, the SES light originally came on when the fuel tank was REALLY low (I've never had the tank under a quarter, let alone how low it was that day) and the code in INPA is showing misfire with fuel cut.

Any ideas of where to look next would be great, I would prefer to stop just throwing parts at the thing until I get lucky and fix it.
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      02-15-2018, 08:54 AM   #2
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Have you done a compression test ? Leak Down ?
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      02-15-2018, 10:57 AM   #3
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I've run my tank down to where the range says "---" and never had a problem - going below 1/4 tank isn't going to hurt your engine (I usually run it down to 10-15 miles range). I literally had 0.1 gallons left (tank is 16.4 gallons with the reserve, I filled it back up with 16.3 gallons, lol).

are you getting codes for a misfire? what RPM is your idle normally at?
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      02-15-2018, 11:06 AM   #4
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Quote:
Originally Posted by hassmaschine View Post
I've run my tank down to where the range says "---" and never had a problem - going below 1/4 tank isn't going to hurt your engine (I usually run it down to 10-15 miles range). I literally had 0.1 gallons left (tank is 16.4 gallons with the reserve, I filled it back up with 16.3 gallons, lol).

are you getting codes for a misfire? what RPM is your idle normally at?
15?!
Legendary...
Now I don't feel too awful when I bring it down to 30!
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      02-15-2018, 11:17 AM   #5
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at 30 miles you're not even into the reserve yet.
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      02-15-2018, 06:06 PM   #6
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Quote:
Originally Posted by Bavarian Tech View Post
Have you done a compression test ? Leak Down ?
I have not done compression, leak down, or fuel pressure test yet. That would be a hell of a coincidence to have a valve seal leak or compression issue right after replacing the injectors.

I'll have to go dig out the compression tester and check. I also think I'll swap injectors to see if it moves with the injector. I wouldn't think brand new OEM injectors would have an issue, but I've obviously been wrong up to this point.

Anyone know what the compression should be on the n52 right off?
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      02-15-2018, 08:04 PM   #7
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there's no absolute value. You have to measure each cylinder (with the throttle wide open), and they should be within 5% of each other. If one cylinder is lower, then you would do a leakdown test.
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      02-15-2018, 09:51 PM   #8
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Quote:
Originally Posted by HeyYoVio View Post
I have not done compression, leak down, or fuel pressure test yet. That would be a hell of a coincidence to have a valve seal leak or compression issue right after replacing the injectors.

I'll have to go dig out the compression tester and check. I also think I'll swap injectors to see if it moves with the injector. I wouldn't think brand new OEM injectors would have an issue, but I've obviously been wrong up to this point.

Anyone know what the compression should be on the n52 right off?
In 7+ years at a dealership I've never heard or seen a N52 fuel injector go bad.. Far as spec 9-18 BAR depending on position of Valvetronic with a maximum deviation of 2 bar
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