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so I took the car to the shop and they refused to weld in the universal cats telling me it will cause an efficiency code and won’t pass inspection so they won’t do the work as I pulled up to the shop. I got a code P2099 bank 2 is Rich post cat as I was driving home I noticed at certain points Fuel trims on bank one and bank two were spiking up to 15%. now I know I hear rattling from my bank 2 catalytic converter, but now I’m wondering if this is really a matter of replacing the cat or if there is another issue and also how can I replace with universal cats and avoid failing an emissions test for an efficiency code after the fact?
The long story short is you got to find why your engine combustion is too rich.
For now ignore the short trim (STFT), only consider LTFT at idle.
Causes may be:
Marginal ignition
Injector issue
Worn Cylinders
Misc...
> Sh!@#T Rolls Downstream...
A rich upstream fuel trim guarantees a rich downstream fault.
Too much fuel does melts cats.
Fixing the upstream issue is the first step ahead of cats!!
The long story short is you got to find why your engine combustion is too rich.
For now ignore the short trim (STFT), only consider LTFT at idle.
Causes may be:
Marginal ignition
Injector issue
Worn Cylinders
Misc...
> Sh!@#T Rolls Downstream...
A rich upstream fuel trim guarantees a rich downstream fault.
Too much fuel does melts cats.
Fixing the upstream issue is the first step ahead of cats!!
Miami Beach rush hour
well, the only thing I can think to do is pull the bank2 spark plugs and try to see which one looks off and do a smoke test and see what I get. I’m assuming the best place to plug in the smoke machine is one of the secondary air injection hoses on the front of the supercharger is that correct?
also, I have a hard time believing that the possible issues you listed wouldn’t throw any codes I mean, I would tend to think if I had a problem with the ignition I’d be getting codes for ignition related issues or if I had a vacuum leak I’d have an on meter error code unless there’s certain vacuum lines that won’t trigger an unmetered error code and I would think that if a fuel injector was dropping out, it would also set off a code I’m not saying you’re wrong. I’m just wondering why I’ve only had that p2099 code pop today and it’s the only code to date
Last edited by Apjcustoms; Mar 12, 2026 at 05:15 PM.
well, the only thing I can think to do is pull the bank2 spark plugs and try to see which one looks off and do a smoke test and see what I get. I’m assuming the best place to plug in the smoke machine is one of the secondary air injection hoses on the front of the supercharger is that correct?
also, I have a hard time believing that the possible issues you listed wouldn’t throw any codes I mean, I would tend to think if I had a problem with the ignition I’d be getting codes for ignition related issues or if I had a vacuum leak I’d have an on meter error code unless there’s certain vacuum lines that won’t trigger an unmetered error code and I would think that if a fuel injector was dropping out, it would also set off a code I’m not saying you’re wrong. I’m just wondering why I’ve only had that p2099 code pop today and it’s the only code to date
Your Bk2 earning a lean trim is not caused by your failing downstream cat - The upstream exhaut O2/Lambda sensors ignore cats to set trims...
Earlier on in post 23:. you had identified an odd running cylinder: focus on that.
The cat is unlikely gonna help.
Pin point one or more Bk2 rich cyls.
Identify which cylinder has issues (No 5?)
then figure out what makes it run rich?
bad ignition
leaky injector
compression loss
It's easier to focus on one cyl if possible rather than test everything on every cyls.
Last edited by CaliBenzDriver; Mar 12, 2026 at 09:56 PM.
I replaced all o2 sensors codes are gone trims are even at 5% . replaced CPS with oem MERCEDES sensor that resolved the cranking issue . still have strange stumble and whoosing sound under heavy load . smoke tested and can't find any leaks
I replaced all o2 sensors codes are gone trims are even at 5% . replaced CPS with oem MERCEDES sensor that resolved the cranking issue . still have strange stumble and whoosing sound under heavy load . smoke tested and can't find any leaks
Good progress was made!
Long cranks and Cam sensors go hand in hand.
Now you still have stumble under heavy load... thats likely from lean (LTFT:5%Trim?) ... suspect fuel delivery issue.
Good progress was made!
Long cranks and Cam sensors go hand in hand.
Now you still have stumble under heavy load... thats likely from lean (LTFT:5%Trim?) ... suspect fuel delivery issue.
I’ve been told ltft that are close and low such as 5% were good numbers 🤔 well I tested fuel pressure and it’s within spec and held pressure after I killed engine
quote -Long Term Fuel Trims (LTFT) on the Mercedes-Benz M113K engine should ideally fluctuate between \(-5\%\) and \(+5\%\). Values consistently exceeding \(\pm 10\%\) indicate an underlying issue, while anything beyond \(\pm 25\%\) will trigger a Check Engine Light. [1]
Last edited by Apjcustoms; May 15, 2026 at 01:37 PM.
I’ve been told ltft that are close and low such as 5% were good numbers 🤔 well I tested fuel pressure and it’s within spec and held pressure after I killed engine
quote -Long Term Fuel Trims (LTFT) on the Mercedes-Benz M113K engine should ideally fluctuate between \(-5\%\) and \(+5\%\). Values consistently exceeding \(\pm 10\%\) indicate an underlying issue, while anything beyond \(\pm 25\%\) will trigger a Check Engine Light.
5% LTFT is a fine working trim number.
Best part is both banks are equal now you have trusted O2 sensors.
5% says your engine has enough air (MAF!) but not enough petroil.
Based on that data: your ignition is proven good - No need to mess with it.
LTFT should not fluctuate at steady hot idle Rpm - they are fixed unlike ShortTerm numbers.
> PRACTICALLY....
Your static fuel pressure test is not really significant.
You need to witness pressure delivered under engine load condition.
> STUMBLES = LEAN MISFIRES....
The fuel injection relies on fixed predictable pressure to manage A/F mixtures with precision.
When mixtures are too lean, the wholesale misfires materialize as stumbles from many combustion cycles being non-contributing.
Last edited by CaliBenzDriver; May 15, 2026 at 02:21 PM.
Best part is both banks are equal now you have trusted O2 sensors.
5% says your engine has enough air (MAF!) but not enough petroil.
Based on that data: your ignition is proven good - No need to mess with it.
LTFT should not fluctuate at steady hot idle Rpm - they are fixed unlike ShortTerm numbers.
> PRACTICALLY....
Your static fuel pressure test is not really significant.
You need to witness pressure delivered under engine load condition.
> STUMBLES = LEAN MISFIRES....
The fuel injection relies on fixed predictable pressure to manage A/F mixtures with precision.
When mixtures are too lean, the wholesale misfires materialize as stumbles from many combustion cycles being non-contributing.
I don’t know that it’s a misfire and wouldn’t that log as a misfire especially if it was serious enough to shut down power to the engine in such a manner ? I have on a couple occasions when driving the vehicle for extended periods of time over an hour or so got the notification for the gas cap, but I’ve never gotten a notification for the gas cap any other time. Also couldn’t a blockage in a catalytic converter cause these exact symptoms where upon heavy load if the exhaust was struggling to flow produce the sound and the stumble.?
I don’t know that it’s a misfire and wouldn’t that log as a misfire especially if it was serious enough to shut down power to the engine in such a manner ? I have on a couple occasions when driving the vehicle for extended periods of time over an hour or so got the notification for the gas cap, but I’ve never gotten a notification for the gas cap any other time.
Also couldn’t a blockage in a catalytic converter cause these exact symptoms where upon heavy load if the exhaust was struggling to flow produce the sound and the stumble.?
You should explore these other possibilities... never know
There's a possibility your tank high vacuum is starving the engine. See EVAP faults testing.
Fuel pressure test would catch that issue, right?
Last edited by CaliBenzDriver; May 15, 2026 at 04:59 PM.
Try to focus your efforts on one item then the next one and the next one until you nail your issue.
We said fuel delivery issue...
You said something about tank vacuum...
Very fair chance that way
Then pick what you are comfortable working with to test that :
Live fuel pressure or ?
tank vacuum gauge ?
needless to say...
fuel leaking on hot exhaust is flammable 🤞
Choice is to either replace countless good parts or to troubleshoot your issue Taipei, Airport Taxi
so I drove the car for three hours straight yesterday in stop and go traffic and long straight on the highway I’m leaning towards a boost leak. I had lbought a used bypass valve and I don’t see any fittings on it that accept a vacuum line also upon visual inspection with my bore scope I didn’t see any signs of a compromised gasket or seal around the bypass valve . When replacing the valve cover gaskets, I ended up with a vacuum leak because the rubber grommet on the evap line that runs into the rear of the super charger fell off so I siliconed it back into place . Is there any chance siliconing that grommet and line could cause this seeing as this issue arose after that incident?
also after listening to the sound with the expressed intention of trying to describe it I noticed it reminds me of when an older cars clutched AC compressor is going bad and feels similar . does that mean its not a boost leak no it doesn't but im trying to give as much information as possible
so I drove the car for three hours straight yesterday in stop and go traffic and long straight on the highway I’m leaning towards a boost leak. I had lbought a used bypass valve and I don’t see any fittings on it that accept a vacuum line also upon visual inspection with my bore scope I didn’t see any signs of a compromised gasket or seal around the bypass valve . When replacing the valve cover gaskets, I ended up with a vacuum leak because the rubber grommet on the evap line that runs into the rear of the super charger fell off so I siliconed it back into place . Is there any chance siliconing that grommet and line could cause this seeing as this issue arose after that incident?
Yes, a defective PCV system can be a qualified source of air the MAF don't get to sense through.
At some point you need to pick your battles to focus instead of lengthening a short list...
fuel supply
tank EVAP
PCV leak
....
You do that by testing the functions you suspect.
Last edited by CaliBenzDriver; May 19, 2026 at 02:30 AM.
Yes, a defective PCV system can be a qualified source of air the MAF don't get to sense through.
At some point you need to pick your battles to focus instead of lengthening a short list...
fuel supply
tank EVAP
PCV leak
....
You do that by testing the functions you suspect.
1- short of watching the fuel test gauge while driving all the numbers were where they should be
2- I’ve done a couple searches on how to test tank evap I assume I’ll have to break out smoke machine again for that
3- smoked the pcv system via the evap & brake boost line no leaks detected on the engine side of things
4- is there a way for my to calibrate or monitor the bypass valve on the super charger ?
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