Mr. Lin

Reason I ask is because I will be on my third one in a year and it's always bank 1 sensor 1 and it's always the same P0133 and/or P2237 codes. I've replaced it each time with a Bosch 17016. Ever since I installed the EC V5 tune about 6 months ago, I started noticing a rotten egg smell that I hadn't in the past, even after the spirited driving I used to do regularly. I haven't had much chance to try and find a possible exhaust leak, but any suggestions would be more than welcome. It's a 2008 with almost 74k miles if that makes any sort of difference.

Vladds

Take a look at the trims with an obd2 reader, as you drive. See what the ECU is doing: adding fuel, subtracting fuel?
The smell is associated with improper AFR.

I am Jeff

If you are using aftermarket air filters, you should make sure that they are properly seated. If the MAF sensors readings are off, it can throw off your AFR and foul up your sensor...

Mr. Lin

drove home, parked it in the garage, plugged in my iCarsoft980 to check fuel trims.

STFT B1: -2.3%
LTFT B1: 3.9%
STFT B2: 2.3%
LTFT B2: 12.5% <------ this sucker right here...

makes me wonder tho... unless my scanner doesn't know which bank is which, shouldn't this be B1's whacked fuel trim?

My filters are stock. Maybe I'll hit the MAFs with some cleaner.

Jasonoff

LTFT is high so you probably have an air leak b̶e̶f̶o̶r̶e̶ after the MAF on that side. It's making it run too rich fouling the O2.

ItalianJoe1

Air leak before the MAF won't do anything, it will still measure the air.

If you have high fuel trims, you have a leak AFTER the MAF, meaning there is unmetered air getting into the engine. This case there is 12% too lean on that side, so it's adding fuel to compensate. If this is correct, it's not going to effect your exhaust smell or anything. If there isn't a leak, and either the MAF or O2 sensor is reporting a faulty value, then the car is falsely adding fuel, which can be bad. Need to figure out what's the actual cause of the fuel trim change.

Rotten egg smell is usually a catalytic converter dying.

Vladds

This is correct, there is a source of un-metered air, downstream of the MAF.


Here is what happens with this: The Oxygen sensor is not enough to get the fueling and the AFR right, otherwise there would not have been a MAF in the design of the car from the get-go.
Not having accurate data that is sufficiently sensitive to the volume of air coming in and relying on slow-er exhaust gas trend data, the amount of fuel injected is in error. It is designed to err rich.
A lean error would cause high EGT's and kill a non metal substrate converter.
So the ECU, using the fuel trim compensates, in hopes mostly to protect the converters. The compensation is not 12.5%, but 14.8% momentary and its important to note that it's on a growing path, will probably stabilize around 15% in hot idle.
The code threshold is probably in the 20-25%.
The result is that with two banks and only one rich, there will be a degree of imbalance in fueling especially in idle and there will be an amount of vibration.


Now it's difficult to figure what causes the smell, if it's the rich condition that sets in once the compensations take hold, or the lean condition that happens after you get off the accelerator (an intake manifold air leak will become less relevant as you accelerate and drive, because the volume of unmetered air becomes small compared with what air the engine can gulp at WOT, especially a M156).


But I've been tinkering with cars for a long time and back in 1997 I was curios about this and tested it with a VW scirocco. This still had the continuous mechanical high pressure fuel injection and most importantly a mixture screw.
So I deliberately leaned it out, richended out and.... sniffed the gasses.
The lean smells like rotten egg
The right mixture idle causes a lot of water condensation, sprays those drops
The rich has a smell similar with ink.


Now, OP here's my recommendation:


Get the torque specs for the aluminum bolts that secure the intake manifold. I have them, but am in the middle of many things, so if you can't find them let me know and I'll locate them.


It will be difficult to impossible to figure which side the bank 1 is. If the factory dropped a reference to this in the WIS, that would be nice, but I wouldn't bank on that. SO you will need to tighten both banks, especially since the manifold is one unit and mechanically it would not be right to compromise the torque sequence, to bias one side.


So the torque procedure for the manifold has 3 sequences:
1. Torque to value
2. turn 90 degrees
3. turn 10 degrees


Do this:
1. recertify the torque figure, just apply the value on the torque wrench in the proper sequence (half the bolts were loose on mine)
2. give it an additional 45 degrees. This did not snap the bolts on mine.


Now realize that there is a certain danger there with the aluminum bolts, it's not entirely impossible that one of them would snap, be warned of this.


But in the case of my bolts, as soon as I did this procedure, the trims went in idle both to what you have on Bank 1. The gas mileage went up, the smell was gone and the idle was noticeably smooth. Both my banks were out, as far as trims.


So, because I liked the increased gas mileage, I decided to try for one additional MPG by actually changing the intake manifold gaskets.


Sorry for the long story, hopefully has good info for you.

Jasonoff

Right, my bad. Meant to say post MAF.

ItalianJoe1

In reference to Vladds post, bank 1 is the right side (passenger here in the US), bank 2 is the left side. This is the same on almost every MB engine.

Mr. Lin

this is from today. bet I have the IM leak

also, that's what I thought. I've always changed the passenger side O2 sensor and the codes for B1S1 go away.
makes me wonder then why B2 trims are the ones showing mass correction.

Diabolis

The rotten egg smell indicates that the cats can't clear out all the hydrogen sulphide. Assuming that you have properly functioning catalytic converters and that the issue is with the AFR, you're likely to get the rotten egg smell when your mixture is too rich. Now, LTFT depends on the STFT. The STFT is set during closed loop conditions to stay at the optimal 14.7 AFR at idle. So - if the car is running lean in closed loop, it will add fuel in order not to blow the motor which is likely causing the high LTFT reading. If you have replaced the O2 sensors, I'd be looking for a vacuum leak, a faulty MAF or possibly a bad spark plug or coil in the affected bank. The ECU tune is not going to affect the two banks differently.

Vladds

Just to confirm, in terms of Xentry, right side is US passenger side?
So if Xentry logs something for right side and you go to replace that item, it will be the passenger side? (as opposed to ... say looking at the engine, standing in front of it and its right side)

Mort

Yes, Left and right references in an automobile always refer to the driver's left and right side or hand sitting in the normal driving position behind the steering wheel. In North America cars are normally Left Hand Drive and the left side is the driver's side and the right side is the passenger's side. In other markets cars might normally be Right Hand Drive (such as England and Australia ) and the left side is the passenger's side and the right side is the driver's side. The right and left side of a car is consistent in all markets but the driver's and passenger's side reference will vary depending on if the car is Left Hand Drive or Right Hand Drive.