Intermittent Bank 2 Misfire and Rough Idle

[Contra]

Originally Posted by RocketyMan

Was it a supercharged engine? Hmmm...I have heard of part of the interior tube part cracking. Interesting...

Never been supercharged to my knowledge. Replaced the O2 sensor this morning and that changed nothing. Still super rough cold start. Lots of crackling from the driver side exhaust pipes while the passenger side sounds normal, and a pretty strong gas smell.

Drove it to the shop and it drives fine once warm. They’re going to take a look tomorrow morning.

[Ajolives]

Originally Posted by Contra

Never been supercharged to my knowledge. Replaced the O2 sensor this morning and that changed nothing. Still super rough cold start. Lots of crackling from the driver side exhaust pipes while the passenger side sounds normal, and a pretty strong gas smell.

Drove it to the shop and it drives fine once warm. They’re going to take a look tomorrow morning.

Sounds like it could a header to manifold leak to me; when the car is warmed up the metals expand and the leak would be not as noticeable. Hopefully it’s nothing serious.

[Redd]

Just so you know, constant misfires can damage the O2s. I'd put the old ones back until you fix the issue.

[Contra]

Originally Posted by Ajolives

Sounds like it could a header to manifold leak to me; when the car is warmed up the metals expand and the leak would be not as noticeable. Hopefully it’s nothing serious.

Header to manifold? You talking about the header to primary cat connection? The header and manifold are the same thing. Or do you mean the header to the block joint?

The header to primary cat gaskets are brand new, along with the bolts and nuts, so I doubt that.

Also, the shop gave me a call this morning. They did some live data monitoring and my long-term fuel trim for bank 2 was fluctuating a lot (like short-term should be reading) and the short-term fuel trim read “0” / no signal. They suspect it’s a broken wire / pin within the plug for the O2 sensor and the computer is just dumping too much fuel due to the lack of signal.

They’re gonna do some more investigation and I’ll update results as I get them.

[RocketyMan]

Originally Posted by Contra

Header to manifold? You talking about the header to primary cat connection? The header and manifold are the same thing. Or do you mean the header to the block joint?

The header to primary cat gaskets are brand new, along with the bolts and nuts, so I doubt that.

Also, the shop gave me a call this morning. They did some live data monitoring and my long-term fuel trim for bank 2 was fluctuating a lot (like short-term should be reading) and the short-term fuel trim read “0” / no signal. They suspect it’s a broken wire / pin within the plug for the O2 sensor and the computer is just dumping too much fuel due to the lack of signal.

They’re gonna do some more investigation and I’ll update results as I get them.

Thanks for reporting back! So that is good the now data is being reviewed through this diagnosis.

It is normal during a cold start for the engine to sound pretty crappy as the engine start strategy pulls timing in efforts to heat up the cats more quickly.

Well if you suspect the car is running very rich, then it IS POSSIBLE you could have a leaky injector on bank 2--and this is not unheard of happening on the S65/S85 engines. I don't see how it could be a broken wire if you don't have any codes for the O2 sensor wiring. For instance, the heater circuit or pump cell. It can be easy enough tho to test this from the DME connector to the LSU connector.

When you changed the oil, did it smell pretty "gassy?"

[Contra]

Originally Posted by RocketyMan

Thanks for reporting back! So that is good the now data is being reviewed through this diagnosis.

It is normal during a cold start for the engine to sound pretty crappy as the engine start strategy pulls timing in efforts to heat up the cats more quickly.

Well if you suspect the car is running very rich, then it IS POSSIBLE you could have a leaky injector on bank 2—and this is not unheard of happening on the S65/S85 engines. I don't see how it could be a broken wire if you don't have any codes for the O2 sensor wiring. For instance, the heater circuit or pump cell. It can be easy enough tho to test this from the DME connector to the LSU connector.

When you changed the oil, did it smell pretty "gassy?"

Yeah I’m aware of the secondary air system on cold start making the car sound like farm equipment for a little while, but this was different.

I’ve read some leaky injector horror stories causing hydrolock, but if the injector was stuck open I imagine the misfire would be localized to 1 cylinder and not all 4.

Didn’t really smell the oil too much when I changed it, but I did get it blackstone analysed and they mentioned slightly lower viscosity, but no fuel contamination.

[RocketyMan]

Interesting oil report. Has the shop come back yet with any update on checking the wiring of the O2 sensor?

[Contra]

Originally Posted by RocketyMan

Interesting oil report. Has the shop come back yet with any update on checking the wiring of the O2 sensor?

No updates yet, and I probably won’t get any until Monday. Per the shop their BMW Master Tech is booked up with other cars and likely won’t get to mine until late Friday or Monday. They just did a quick scan to verify my issues and gave me a call for maintenance background and more info.

I’ll be sure to update this thread when I hear something back.

[aggieshan]

Any update from the shop?

[Contra]

Originally Posted by aggieshan

Any update from the shop?

Just got an update a few hours ago. The checked the wiring and everything seems correct. They tried swapping the O2 sensors from bank 2 to bank 1 and vice versa and the codes remained on bank 2.

They suspect something may be wrong with the DME because the long term and short term fuel trims seem reversed. The short term remains stable while long term fluctuates a lot.

They’re going to try a fresh OEM DME flash, then try disabling the secondary air system via tune in case that is somehow the issue. If that doesn’t work they think I may need a new DME….

They’re going to get the DME Flash and secondary air done tomorrow or Wednesday and then give me a call. Fingers crossed.

[aggieshan]

Thanks for the updates. Has the car been tuned before? My car has again developed similar misfire. Last time, it was due to overfill oil. It seems to fix the problem but after a year, misfire bank 2 has returned.

My car had Alpine tune before my ownership. I flashed it back to stock file right after i bought the car. i am very curious on how DME could cause the problem.

[Contra]

Originally Posted by aggieshan

Thanks for the updates. Has the car been tuned before? My car has again developed similar misfire. Last time, it was due to overfill oil. It seems to fix the problem but after a year, misfire bank 2 has returned.

My car had Alpine tune before my ownership. I flashed it back to stock file right after i bought the car. i am very curious on how DME could cause the problem.

The car has never been tuned under my ownership, but the previous owner was straight piped for a while before I purchased it. I would not be surprised if it was tuned and is doing weird stuff now that it has an OEM X pipe on it.

[Johal E32]

Following.. Please let us know what the shop ends up repairing.diagnosing on your car.

[Contra]

7/18/23 Update:

The Master Tech at the shop gave the data another look and believes that the short term fuel trim on bank 2 is reading "0" due to one of the secondary air valves being stuck and flooding that side of the exhaust with too much air.

They believe that all that air is causing the primary O2 sensor to read that the mixture is severely lean and "out of range" causing it to return a "0" for short term trim.

Due to the sensor reading a lean mixture, the DME is compensating by dumping more fuel than required, causing the misfires and very rich exhaust mixture.

The master tech feels the DME is not the problem. I didn't realize he hadn't made a call on it and the possible DME failure was just the front desk guy hypothesizing..... which is slightly annoying.

I spent 30mins or so on the phone with the tech instead of the service guy this time and he explained what he thought the issue was and gave them the go ahead to replace the secondary air valves and hoses.

I'll update again when the work is done / if anything changes with my diagnosis.

[aggieshan]

Very interesting theory. It kind of explains why it only happens on one bank and happens during cold start up or does it only happen at cold start?

Here is a good clip talking about secondary pump issue with picture of secondary pump valves attaching to each bank.
https://youtu.be/ZAq_2k0VG4Y

[Contra]

Originally Posted by aggieshan

Very interesting theory. It kind of explains why it only happens on one bank and happens during cold start up or does it only happen at cold start?

Here is a good clip talking about secondary pump issue with picture of secondary pump valves attaching to each bank.
https://youtu.be/ZAq_2k0VG4Y

It only happens while the engine is not up to temperature. The cold start after sitting overnight or longer is definitely the most severe though. As the car warms it gets better.

[Contra]

7/21/23 Update:

The shop replaced the secondary air valves, secondary air pump and associated tubing, and the bank 2 pre-cat O2 sensor and all the codes have cleared and the car is running well (per them). I am going to pick up the car tonight or tomorrow. They drove it 30 miles and turned the car off and restarted it several times with no errors posting.

When the valves were pulled, the bank 1 valve was packed with carbon buildup, and refused to open even with compressed air being fed into it. The tech got it to open after knocking some carbon out of it. Pictures attached.

The shop also recommended I replaced the other pre-cat O2, and both of the post-cat O2 sensors just so they were all new. I have ordered those 3 sensors from FCP euro and will install them myself when they arrive.

Hopefully this is the end of my issues. Wasn't cheap ($3200), but I'll be glad to have it running well again.

I'll post here again if it comes back, but I am hopeful this will be the last update.

[DrFerry]

Originally Posted by Contra

7/21/23 Update: The shop replaced the secondary air valves, secondary air pump and associated tubing, and the bank 2 pre-cat O2 sensor and all the codes have cleared and the car is running well (per them). I am going to pick up the car tonight or tomorrow. They drove it 30 miles and turned the car off and restarted it several times with no errors posting.

When the valves were pulled, the bank 1 valve was packed with carbon buildup, and refused to open even with compressed air being fed into it. The tech got it to open after knocking some carbon out of it. Pictures attached. The shop also recommended I replaced the other pre-cat O2, and both of the post-cat O2 sensors just so they were all new. I have ordered those 3 sensors from FCP euro and will install them myself when they arrive.

Hopefully this is the end of my issues. Wasn't cheap ($3200), but I'll be glad to have it running well again. I'll post here again if it comes back, but I am hopeful this will be the last update.

Thanks for taking the time to follow up and provide a status update for the community. I'm glad to know your car is now running well again. When I see that much carbon (pictured on the floor) it makes we wonder "if" at some points in time the engine oil was not 100% synthetic. High quality, brand name 100% synthetic oil doesn't typically turn to ash/coke/carbon as badly or as much as with conventional oil. This is due to synthetic oils using more heat stable ester base(s) in their formulations.

How many owners has your car had? Have you ever seen the underside of the valve covers and checked for carbon build up. Are the piston rings okay (compression test). Seeing that much carbon deposition also makes me wonder about carbon build up on the inlet and exhaust valve stems, valve guides and seats as well as the PCV valve. It's something to be on the look out for and if confirmed attempt some mitigation (decarbonize) because the motor might be burning quite a bit of oil IMO (piston rings?).
.

[Contra]

Originally Posted by DrFerry

Thanks for taking the time to follow up and provide a status update for the community. I'm glad to know your car is now running well again. When I see that much carbon (pictured on the floor) it makes we wonder "if" at some points in time the engine oil was not 100% synthetic. High quality, brand name 100% synthetic oil doesn't typically turn to ash/coke/carbon as badly or as much as with conventional oil. This is due to synthetic oils using more heat stable ester base(s) in their formulations.

How many owners has your car had? Have you ever seen the underside of the valve covers and checked for carbon build up. Are the piston rings okay (compression test). Seeing that much carbon deposition also makes me wonder about carbon build up on the inlet and exhaust valve stems, valve guides and seats as well as the PCV valve. It's something to be on the look out for and if confirmed attempt some mitigation (decarbonize) because the motor might be burning quite a bit of oil IMO (piston rings?).
.

The same shop did both valve cover gaskets for me and did not mention any concerns with the valve train.

I am the 3rd owner, and the 2nd owner owned the car from 21,000miles to 72,000miles and used LiquiMoly full synthetic 10W-60 and did blackstone analysis every oil change. I also do blackstone every oil change and use the OEM BMW synthetic oil.

The carbon buildup pictured is on the exhaust side of the valve, so I’m not sure oil has anything to do with it. Probably just a product of the car running rich for a good portion of its life due to exhaust leaks and the previous owner had straight piped at some point. I’ve been troubleshooting exhaust leaks for nearly my entire ownership haha.

Regarding the car burning oil, my car burns/leaks (one of my valve covers is warped and leaks a bit even after gasket replacement) about 1 to 1.5qt between 7500 mile oil changes which seems to be on par with what many people experience with these cars.

[Redd]

Thanks for the update. You've convinced me to do a SAP delete.

[aggieshan]

Thanks for the update. I will look into secondary valve as well. Any reason why they replaced secondary air pump? Is it just for peace of mind?

[spammysammich]

If your valves can’t close exhaust burns up the air pump.