[NavyBlues]

Apologies if this is in the wrong place.

Long time lurker, but my e90 335i has been in the shop for nearly three weeks and they can't figure out what's wrong with it. Hoping to crowdsource some possibilities.

Brought it in for a running lean SES fault.

Original issue with vehicle to be addressed was check engine light - lean fault stored for bank 2 - fault 29E1.

Indy smoke tested the intake tract and found major leak from rear of engine. Raised, removed belly pan(s), and found intake boot separated from bank 2 turbocharger inlet, allowing unaccounted for air into engine. This engine is not equipped with a mass air meter, but uses the primary oxygen sensors (wideband) and two MAP sensors to determine airflow.

They then replaced both plastic pipes to turbochargers and offered to change the turbos themselves. (They're fine, w/ minimal rattle, I politely declined).

They started engine after repairs and immediately noted multiplicative fuel trim values going to +30% on both banks, indicating that the DME was seeing a lean condition and adding fuel to compensate.

They smoke tested intake tract again and found a very minor leak at the intake tube to the vacuum pump. Sealed as necessary, and found no further leaks.

Thinking it might be a dirty oxygen sensor they swapped in two known good primary oxygen sensors to be sure that the readings were correct from the existing sensors - condition remains.

They checked high pressure fuel system pressure. Rail pressure sensors reports between 48 and 52 bar at idle, within spec. The HPFP is the most recent iteration (106?) and is just over a year old with just over 10,000 miles on it.

I thought I might've gotten some crappy gas and they performed ethanol content test on fuel in tank - found it to be at 20%. Higher than allowable. Drained fuel from both sides of tank and filled with 5 gallons of E10 pump gas (actual measurement 8% ethanol). Condition remains.

Checked low pressure fuel system pressure with mechanical gauge. Fuel pressure is within spec and matches what the low pressure fuel sensor is reporting - at 5 bar at idle (72-75 psi).

Suspected possible weak fuel injector(s), as they were last replaced in 2010. Swapped in known good set of injectors out of another like vehicle. Condition remains.

Here's where it gets interesting: Measured crankcase pressure with digital manometer and compared value to a like and known good vehicle with no issues. Problem vehicle measures -7 to -8 millibar at idle. Known good vehicle measures -17 millibar at idle, holds steady. Spec value is -20 millibar +/-.

So in summary - vehicle came in with a lean fault. Only real source of unmeasured air was repaired. Lean faults remain and fuel trim specifically at idle goes to +30% almost instantly. The crankcase vacuum is out of spec by a fair bit (caused by internal valve cover failure?). We also occasionally get an overboost fault from bank 2 while driving under heavy load (full throttle).

Thoughts on what the problem could be? VCG? OFHG? Thank you!

[sorin1987]

When I had the "too lean.." code I was experiencing engine misfires as well. It was quite tricky to diagnose in my case also but for me it was a cracked Valve Cover. That fixed the issue for me. The crack was barely noticeable with the naked eye. I would replace that if it was never replaced and your car has more than 70k miles, it is not an expensive part.

[NavyBlues]

Originally Posted by sorin1987

When I had the "too lean.." code I was experiencing engine misfires as well. It was quite tricky to diagnose in my case also but for me it was a cracked Valve Cover. That fixed the issue for me. The crack was barely noticeable with the naked eye. I would replace that if it was never replaced and your car has more than 70k miles, it is not an expensive part.

Thanks for the suggestion. The car has about 105K miles. Figured I'd run her into the ground, just didn't think it might come this soon.

[tan_rich]

Possible it could be the post cat o2 sensors, they provide input for your long term fuel trims. Which in turn affect your short term...

Originally Posted by sorin1987

it was a cracked Valve Cover

I was going to suggest this as well.

[NavyBlues]

Okay so we replaced the valve cover and the gasket, which took care of the oil leak. The car still is getting a running lean fault. Thinking maybe a seal? We've already swapped out the O2 sensors with known working O2 sensors, twice. Same issue persists. Perhaps the DME is bad? Does that even happen?

[RSL]

Not always easy to tell if it's the chicken or the egg, but if you have misfires on all 3 bank 1 cylinders, leaning towards trim (O2) or a remaining blockage causing the misfires since either affect the entire bank and will have similar symptoms. Your REAR bank 1 O2 is wacky, but can't tell if misfires or a blockage are causing the readings or the readings are causing the misfires. Rears are controls for primary O2s, which in turn control trims and your trims are clearly jacked up.

All O2s may be fine and could be that you still have a mess of blown out cat material piled up on/in the secondary cat or the secondary cat has disintegration problems as well. Less back pressure just means there's enough of a leak to not hold as much air, it doesn't necessarily mean the path for flow isn't obstructed or isn't blocking flow at higher volume/velocity. Might not be enough to be definitive, but start the car and feel the air coming out of the exhaust tips at the same time with at constant rev for a quick check (with the driver side exhaust valve open). It would be best to pull the exhaust and verify the midcats condition visually with a scope or bolt up a known good exhaust and run it if available.

Injector MOSFET issues on MSD81 would be beyond rare.

[NavyBlues]

Originally Posted by RSL

Not always easy to tell if it's the chicken or the egg, but if you have misfires on all 3 bank 1 cylinders, leaning towards trim (O2) or a remaining blockage causing the misfires since either affect the entire bank and will have similar symptoms. Your REAR bank 1 O2 is wacky, but can't tell if misfires or a blockage are causing the readings or the readings are causing the misfires. Rears are controls for primary O2s, which in turn control trims and your trims are clearly jacked up.

All O2s may be fine and could be that you still have a mess of blown out cat material piled up on/in the secondary cat or the secondary cat has disintegration problems as well. Less back pressure just means there's enough of a leak to not hold as much air, it doesn't necessarily mean the path for flow isn't obstructed or isn't blocking flow at higher volume/velocity. Might not be enough to be definitive, but start the car and feel the air coming out of the exhaust tips at the same time with at constant rev for a quick check (with the driver side exhaust valve open). It would be best to pull the exhaust and verify the midcats condition visually with a scope or bolt up a known good exhaust and run it if available.

Injector MOSFET issues on MSD81 would be beyond rare.

Damn, should have mentioned that we checked the cat and its clean. Nice clean honeycomb. Or did I misunderstand. I'll pass this on though. Thank you so much for the input! You rock.

[RSL]

So we're on the same page, I'm referring to the secondary cat in the exhaust piping. Not all models/years have them, but if yours does and you're saying bank 1 secondary has been checked from the front and has clear, straight honeycomb, it's obviously not a potential cause.

https://www.realoem.com/bmw/enUS/showparts?id=VB73-USA-01-2008-E90-BMW-335i&diagId=18_0682

[NavyBlues]

Originally Posted by RSL

So we're on the same page, I'm referring to the secondary cat in the exhaust piping. Not all models/years have them, but if yours does and you're saying bank 1 secondary has been checked from the front and has clear, straight honeycomb, it's obviously not a potential cause.

https://www.realoem.com/bmw/enUS/sho...diagId=18_0682

I'll go back and check tomorrow, but I'm sure he said something about boring in and using a scope.

[NavyBlues]

this morning got started trying to rule out the front and rear crankshaft seals for possible air leakage. We went a fairly non invasive route as There's fairly good access to the seals from underneath the car. There did not seem to be any change by spraying them with cleaner - if there was enough air leakage to cause this issue, I would expect that it would not take much to get a response from the oxygen sensors.

The rear oxygen sensors do influence the overall mixture adaptation of the engine, but the DME focuses on the front sensors, as they are part of the three part mixture control setup on the N54. You have 3 primary sources for mixture control - the MAP sensor in the intake manifold, the MAP sensor in the intake tube ahead of the throttle, and the two primary "wideband" oxygen sensors.

The MS D81 DME referenced is the DME that controls the N55 engine. N54 engines have the MS D80 DME - and they have a high failure rate of the MOSFET transistors that are responsible for creating the high voltage needed to "fire" the piezo injectors. I actually removed the DME from your car, opened it, and checked the resistance of the 6 MOSFET injector driver transistors. They all test normal, so barring a different and uncommon issue with your DME, I believe it is OK.

Here's a link to the procedure: https://us.autologic.com/news/bmw-ms...osis-30ba-30bb

Still stumped.

[NavyBlues]

Originally Posted by RSL

So we're on the same page, I'm referring to the secondary cat in the exhaust piping. Not all models/years have them, but if yours does and you're saying bank 1 secondary has been checked from the front and has clear, straight honeycomb, it's obviously not a potential cause.

https://www.realoem.com/bmw/enUS/showparts?id=VB73-USA-01-2008-E90-BMW-335i&diagId=18_0682

Today's update: Looked at some intake manifold pressure values on a gauge compared to what the DME is seeing from the MAP sensor. I see a little bit of a variation that I will continue to investigate in the morning. I also decided to just for grins pull the intake manifold back and just have a look and make sure nothing looks out of the ordinary, as it was recently off for the carbon blast. I don't see anything abnormal, another dead end.

[RSL]

Sorry, someone else was having single bank and cat problems and for some reason, I was thinking of that in this thread Completely disregard what I said about the secondary cats. If your primary cats were checked and are clear, secondaries should be fine too.

Is the car tuned (E20 in the tank)? E20 *should* be OK on a decently working stock fuel system, but trims will naturally go up to compensate if not specifically adjusted for in the rom and that could potentially cause trim/mixture codes. That's particularly true after changing to/from higher/lower blend with adaptations in place from the prior tank. Were the swapped injectors coded and adaptations reset after the swap and E10 change?

If adaptation resets have not been done, they should be. If they have been done, to no avail on the 29E1, and everything else is working as it should (injectors, coils/plugs, etc.), I'd still check the rear O2s. They haven't been mentioned as looked at/tested and you say you still have the same bank 2 lean issue that car went in with. Rears essentially set the reference point for the primaries, so if a rear is off, the primary will trim as it should, but to an offset value the DME thinks is 1.0 lambda. The lambda values/adaptations can be monitored in INPA if your or your indy has and if a rear sensor voltage is off, it shouldn't be too hard to see (or just swap in a known good bank 2 rear to test if you/indy has one). Speaking of O2s, all 4 are plugged into their correct connectors, right? They are bank specific and can cause issues if reversed and the rears are easy to mix up since the connectors are right next to each other.

Valve cover/PCV is always a possibility and maybe high on the list. I haven't had issues with mine, but they seem to crack left and right around here and can cause all kinds of odd problems. Where are you reading vacuum from on the gauge and what are you using to monitor the DME value?

FWIW, MSD80/81 isn't an N54/N55 thing. MSD80 was only used through early/mid-2008 335s IIRC and then they switched to 81 and continued to use N54s with MSD81 well after N55 came along (335is, 1M, Z4is, etc.). I know you checked your mosfets already, but if you're not sure which your 2008 has, it should be on the label of the DME to verify.

[NavyBlues]

Originally Posted by RSL

Sorry, someone else was having single bank and cat problems and for some reason, I was thinking of that in this thread Completely disregard what I said about the secondary cats. If your primary cats were checked and are clear, secondaries should be fine too.

Is the car tuned (E20 in the tank)? E20 *should* be OK on a decently working stock fuel system, but trims will naturally go up to compensate if not specifically adjusted for in the rom and that could potentially cause trim/mixture codes. That's particularly true after changing to/from higher/lower blend with adaptations in place from the prior tank. Were the swapped injectors coded and adaptations reset after the swap and E10 change?

If adaptation resets have not been done, they should be. If they have been done, to no avail on the 29E1, and everything else is working as it should (injectors, coils/plugs, etc.), I'd still check the rear O2s. They haven't been mentioned as looked at/tested and you say you still have the same bank 2 lean issue that car went in with. Rears essentially set the reference point for the primaries, so if a rear is off, the primary will trim as it should, but to an offset value the DME thinks is 1.0 lambda. The lambda values/adaptations can be monitored in INPA if your or your indy has and if a rear sensor voltage is off, it shouldn't be too hard to see (or just swap in a known good bank 2 rear to test if you/indy has one). Speaking of O2s, all 4 are plugged into their correct connectors, right? They are bank specific and can cause issues if reversed and the rears are easy to mix up since the connectors are right next to each other.

Valve cover/PCV is always a possibility and maybe high on the list. I haven't had issues with mine, but they seem to crack left and right around here and can cause all kinds of odd problems. Where are you reading vacuum from on the gauge and what are you using to monitor the DME value?

FWIW, MSD80/81 isn't an N54/N55 thing. MSD80 was only used through early/mid-2008 335s IIRC and then they switched to 81 and continued to use N54s with MSD81 well after N55 came along (335is, 1M, Z4is, etc.). I know you checked your mosfets already, but if you're not sure which your 2008 has, it should be on the label of the DME to verify.

I'm fairly certain the O2 sensors (all of them) have been checked multiple times, but am reaching back to make sure. I have been losing oil anyway, so we went ahead and replaced the Valve Cover, but the problem persists.

We may have had a breakthrough - the indy tested out an N55 Throttle Body which apparently drove fine, but they couldn't clear the computer because its an N55 and apparently the computer gets cranky, and you can't return a throttle body assembly if they bought one and tried it out and it wound up not being it.

They somehow found an N54 throttle body assembly today that they're testing. I'm hopeful, because the car has been in the shop a month as of tomorrow. Thank you so much for the ideas and your continued input!

[NavyBlues]

Originally Posted by RSL

Sorry, someone else was having single bank and cat problems and for some reason, I was thinking of that in this thread Completely disregard what I said about the secondary cats. If your primary cats were checked and are clear, secondaries should be fine too.

Is the car tuned (E20 in the tank)? E20 *should* be OK on a decently working stock fuel system, but trims will naturally go up to compensate if not specifically adjusted for in the rom and that could potentially cause trim/mixture codes. That's particularly true after changing to/from higher/lower blend with adaptations in place from the prior tank. Were the swapped injectors coded and adaptations reset after the swap and E10 change?

If adaptation resets have not been done, they should be. If they have been done, to no avail on the 29E1, and everything else is working as it should (injectors, coils/plugs, etc.), I'd still check the rear O2s. They haven't been mentioned as looked at/tested and you say you still have the same bank 2 lean issue that car went in with. Rears essentially set the reference point for the primaries, so if a rear is off, the primary will trim as it should, but to an offset value the DME thinks is 1.0 lambda. The lambda values/adaptations can be monitored in INPA if your or your indy has and if a rear sensor voltage is off, it shouldn't be too hard to see (or just swap in a known good bank 2 rear to test if you/indy has one). Speaking of O2s, all 4 are plugged into their correct connectors, right? They are bank specific and can cause issues if reversed and the rears are easy to mix up since the connectors are right next to each other.

Valve cover/PCV is always a possibility and maybe high on the list. I haven't had issues with mine, but they seem to crack left and right around here and can cause all kinds of odd problems. Where are you reading vacuum from on the gauge and what are you using to monitor the DME value?

FWIW, MSD80/81 isn't an N54/N55 thing. MSD80 was only used through early/mid-2008 335s IIRC and then they switched to 81 and continued to use N54s with MSD81 well after N55 came along (335is, 1M, Z4is, etc.). I know you checked your mosfets already, but if you're not sure which your 2008 has, it should be on the label of the DME to verify.

Its not the throttle body. And we've checked and re-checked all sensors, and the problem persists. My 335i has the older, problem-prone MSD80, but the resistance in the transistors has been checked and rechecked. I think they're going to try to pull it out and try another to see if that resolves it. Car's been in the shop for a month as of today and everyone is beyond frustrated and stumped.

[RSL]

Originally Posted by NavyBlues

Its not the throttle body. And we've checked and re-checked all sensors, and the problem persists. My 335i has the older, problem-prone MSD80, but the resistance in the transistors has been checked and rechecked. I think they're going to try to pull it out and try another to see if that resolves it. Car's been in the shop for a month as of today and everyone is beyond frustrated and stumped.

I wouldn't have thought the TB would've been a factor since it affects the entire motor, but at least it's ruled out. If they can verify the DME, great, but a month seems a bit long to diagnose even the oddest of problems. Can you just swap a DME without the CAS? I don't pay much attention to that stuff.

Still some things that aren't clear:
- is it modded?
- is it tuned and, if so, with what?
- was or is there a DP fix installed somewhere?
- have they traced the O2 sensor wires from the sensors to the DME to verify no breaks/shorts?
- checked all the grounds?
- reset adaptations and given it time to relearn with the new injectors/sensors/fuel?
- were the plugs/coils replaced at any point?
- compression/leak down done?
- did they replace the VC / check PCV system?

[torrque]

Originally Posted by RSL

Not always easy to tell if it's the chicken or the egg, but if you have misfires on all 3 bank 1 cylinders, leaning towards trim (O2) or a remaining blockage causing the misfires since either affect the entire bank and will have similar symptoms. Your REAR bank 1 O2 is wacky, but can't tell if misfires or a blockage are causing the readings or the readings are causing the misfires. Rears are controls for primary O2s, which in turn control trims and your trims are clearly jacked up.

All O2s may be fine and could be that you still have a mess of blown out cat material piled up on/in the secondary cat or the secondary cat has disintegration problems as well. Less back pressure just means there's enough of a leak to not hold as much air, it doesn't necessarily mean the path for flow isn't obstructed or isn't blocking flow at higher volume/velocity. Might not be enough to be definitive, but start the car and feel the air coming out of the exhaust tips at the same time with at constant rev for a quick check (with the driver side exhaust valve open). It would be best to pull the exhaust and verify the midcats condition visually with a scope or bolt up a known good exhaust and run it if available.

Injector MOSFET issues on MSD81 would be beyond rare.

I will second this. I found both my cats disintegrated due to engine missfires and causing SES light and lean faults. It was in my case the result of another problem, not the root cause. I had to put in new cats and new O2 sensors (while I was there) and fault never came back.

Here is what I found in my pipes, downstream from the cats:

[NavyBlues]

Originally Posted by RSL

I wouldn't have thought the TB would've been a factor since it affects the entire motor, but at least it's ruled out. If they can verify the DME, great, but a month seems a bit long to diagnose even the oddest of problems. Can you just swap a DME without the CAS? I don't pay much attention to that stuff.

Still some things that aren't clear:
- is it modded?
- is it tuned and, if so, with what?
- was or is there a DP fix installed somewhere?
- have they traced the O2 sensor wires from the sensors to the DME to verify no breaks/shorts?
- checked all the grounds?
- reset adaptations and given it time to relearn with the new injectors/sensors/fuel?
- were the plugs/coils replaced at any point?
- compression/leak down done?
- did they replace the VC / check PCV system?

Thank you ever so much for the continued responses, they're feeding a good conversation with our stumped indy. I'll take your questions in order:

1. Its not modded, fully stock N54 with MSD80. I've contemplated JB4, but I bought the version without the oil cooler, so I've been hesitant to be too aggressive with it.

2. Standard stock tune, as modded by the stealership because of the HPFP issues. (the newest HPFP is currently installed)

3. DP fix? Unclear what you mean. It has been carbon blasted recently though.

4. They're checking the O2 sensor wires and the grounds today, I think.
5. Reset adaptations, given time to learn -- done.
6. Plugs/coils have been replaced and relatively recently. (Plugs were replaced early in this effort)
7. Compression: holy crap I hope its not that. They don't think its mechanical because they would be seeing other codes.
8. VC/PCV - replaced during this business.

They've got an electronics wizard looking at it today, hopefully we learn something.

[Emilime75]

Intake manifold seals at the head? We're those replaced when you did the walnut blast?

[Second325]

Like RSL and torrque said don't forget to check the exhaust. Ask the indy to do a pressure test to rule out clogged cats.

That is what had me stumped for weeks:
https://www.e90post.com/forums/showthread.php?t=1541338

[NavyBlues]

Originally Posted by Second325

Like RSL and torrque said don't forget to check the exhaust. Ask the indy to do a pressure test to rule out clogged cats.

That is what had me stumped for weeks:
https://www.e90post.com/forums/showthread.php?t=1541338

Yep. They pulled the exhaust and took a look at the rear cat. It looked fine.

[NavyBlues]

So they've checked and rechecked everything, including a pressure leak test (passed) and checking the wires between the O2 sensors and the ECU, and all check out. They are concluding that the ECU is corrupt. It had been apparently running lean for so long and compensating for it, that it's now forcing the car to run rich, thinking it's lean when it isn't. The lean running was from the leak in the VCG and the pipe at the back end of the turbo, and the inlets, all of which have been repaired.

So I'm looking at about $1400 for a new ECU. : with a prayer that this finally gets me back on the road. What do you guys think?