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Hi all. After having my valves cleaned, I wanted to see if it changed any of my adaptation values in my camshafts. It did not. I’ve included those adaptation values just for future readers. Before I had my work done I noticed what I thought was a lazy oxygen sensor, but I’ve come here to share the graph and see what people might think. All of the sensors measure in range, but I’m getting some wonky control. I believe my answer is to replace the left downstream O2 sensor….
Don't bother with downstream O2: they monitor the cats effectiveness.
Replace both upstream Lambdas sure!
These are extremely important for fuel trim mixture. They grow lazy slow long before being flagged bad. Dont wait for ECU to call a bad Lambda fault.
They get wasted by carbon contamination or zinc from ZDDP API-SN oils.
Clean Lambda is like running a whole new engine after it being lazy!
Don't bother with downstream O2: they monitor the cats effectiveness.
Replace both upstream Lambdas sure!
These are extremely important for fuel trim mixture. They grow lazy slow long before being flagged bad. Dont wait for ECU to call a bad Lambda fault.
They get wasted by carbon contamination or zinc from ZDDP API-SN oils.
Clean Lambda is like running a whole new engine after it being lazy!
any thoughts on specifically the left banks behavior? What is causing the frequent dips?
any thoughts on specifically the left banks behavior? What is causing the frequent dips?
this is exactly how these sensor work by cycling's up and down.
It lets the ECU know the sensor is truly alive (not bypassed or kaput).
The voltage and the cycles are not directly meaningful to us... what is interesting is what ECU does with that data: Fuel Trims.
These exhaust sensors are related to closed-loop fuel system. Where ECU controls clean-combustion all the way out of the catalytic cleaners.
> FURTHERMORE: GDI ....
These days Bosch has gone further with GDI control.
It creates micro-lean combustion on top of piston cup by injecting right before ignition.
The precise feedback is through CKP rotation in addition to Lambda.
So looking at Lambda signal has limited value. Instead better do some data research with the way ECU track cylinders.
> RESULTS....
In the end the big variable for best combustion is exact timing and thats related to predictable variables.
The ECU cheats realtime computations using historical MAPS to predict how to tune its data. TCU does that also with the ATF clutch pressure.
> TWEAKS....
Once understand the operating mix, you go after minimizing variabilities: frictions, temperature, pressure, voltage, timings, ....
Provide ECU what helps it!
Last edited by CaliBenzDriver; Jul 14, 2025 at 03:34 PM.
Thanks for continuing to think through this with me. I have viewed logs for fuel, cylinders etc and everything is stable matching and "flat". Cat temps are within few degrees of each other.
From my research, this does not seem to be related to an o2 sensor. While I will get to replacing them as a maintenance item, Im not loo excited about doing it and will likely wait until the temperatures die down since I work on my car outside on the ground..
The 02 sensors ahead of the cat should be wavy as they measure combustion going into the cat, and the sensors after the cat should be flat indicating that the cat is working to clean the air. This leads me to believe that the cat is running at less than proper efficiency.
Of course I do make sure to warm up the car, drive aggressively and get the oil and engine very hot.
I think that due to the blow-by I had/ am working on with dirty rings, and the overdoses of ceratec and or the mos2 with sn oils (like you stated Cali), that the cat is a little baked.
Im going to do some further logging and think through my next steps. Im assuming, perhaps incorrectly that the cat is fine but dirty. My next question would be asking "does an inefficient cat have any effect on cam adaptations....and btw, those adaptations are the same regardless of oil solenoid mod or oil weight.
Thanks for continuing to think through this with me. I have viewed logs for fuel, cylinders etc and everything is stable matching and "flat". Cat temps are within few degrees of each other.
From my research, this does not seem to be related to an o2 sensor. While I will get to replacing them as a maintenance item, Im not loo excited about doing it and will likely wait until the temperatures die down since I work on my car outside on the ground..
The 02 sensors ahead of the cat should be wavy as they measure combustion going into the cat, and the sensors after the cat should be flat indicating that the cat is working to clean the air. This leads me to believe that the cat is running at less than proper efficiency.
Of course I do make sure to warm up the car, drive aggressively and get the oil and engine very hot.
I think that due to the blow-by I had/ am working on with dirty rings, and the overdoses of ceratec and or the mos2 with sn oils (like you stated Cali), that the cat is a little baked.
Im going to do some further logging and think through my next steps. Im assuming, perhaps incorrectly that the cat is fine but dirty. My next question would be asking "does an inefficient cat have any effect on cam adaptations....and btw, those adaptations are the same regardless of oil solenoid mod or oil weight.
yes, with that said.... you can jump at 2x Bosch upstream Lambda and not look back!
Sure the cats + downstream O2 are partially unfit from the amount of contaminants + heat but as long as they flow through for your driving style... good enough.
Give them time to clean up somewhat. Downstream won't transform the power profile unless you need to flow WOT...
So upon further logging, I did not find much in terms of mixture adaptation issues, and all components tested in range….
Except when looking at actual fuel pressure. Fuel pressure in the rail was too low and out of spec. And both quantity control valves were out of spec. High pressure and low pressure pumps measured in spec.
please see the pics. I’m ultimately digging around to see if there’s anything else I need to deal with before deciding about extending my warranty.
seemingly I forgot to take the pictures where it showed the angle of the quantity control valve not within spec. It’s supposed to be about 15 and they were in the 30s. This was on both left and right.
Pumps test fine This low rail pressure is what concerns me
Any idea if the quantity control valves are sold separately from the pump? I wasn’t able to find the part number. Located on pump or back of engine?
since the pumps test fine, I wonder if I could get away with the valves for now cause I don’t think the warranty would necessarily cover something like this since it’s not technically failed or throwing a code yet. I do wonder why there’s no code if it’s not reading in the spec they are advising at that engine speed.
I guess I then wonder if this has anything to do with the lambda control which actually looked a little bit better today. I’m inclined to think they’re not related since the mixture adapts and is good..
thx as always.
Last edited by Baltistyle; Jul 15, 2025 at 10:17 PM.
Any idea if the quantity control valves are sold separately from the pump? I wasn’t able to find the part number. Located on back of engine?
since the pumps test fine, I wonder if I could get away with the valves for now cause I don’t think the warranty would necessarily cover something like this since it’s not technically failed or throwing a code yet. I do wonder why there’s no code if it’s not reading in the spec they are advising at that engine speed.
I guess I then wonder if this has anything to do with the lambda control which actually looked a little bit better today. I’m inclined to think they’re not related since the mixture adapts and is good..
thx as always.
These HPFP have the control valve built-in.... we've seen recently HPFP with EXTERNAL pressure regulator valve... that was surprising!
The high-pressure rail uses a sensor for ECU to control the pressure.
Lambdas do not regulate fuel-rail pressure but fuel mixture dosed by injectors.
Let me PM ya'...
So I replaced all four “oxygen” sensors. This fixed the errant wave that was shown above. Still looking into some other items as I move through the systems. Prior to replacement, fuel pressure was back to normal but I am still failing the mixture adaptation tests. Unfortunately, it doesn’t point me to any sort of issue that it’s failing, and it shows all parameters as passed in the screen. I bought a little smoke tester so have been working through all the various vacuum lines check valves, etc.
here’s a pic of the sensors. I won’t share my thoughts until there are some other replies I did this without removing any exhaust components and jammed my hands up in there for the connectors…not pleasant. The sensors came out no problem with a proper o2 wrench and a flex head ratchet, all from underneath, on a jack and jackstands.
White was upstream, not the sensor but the deposit. And look at this ****ery that I found. Manifolds have never been touched and look like it’s been this way for a very long time based on corrosion on the shaft and at the break of the stud.
Last edited by Baltistyle; Aug 8, 2025 at 05:51 PM.
Is that witnessing exhaust sensors jacketed by snow-white ceramics ??
Ceratec can not burn so it goes right through the combustion chambers into exhaust.
Good catch on that exhaust stud walking off !
Yes, good observation in the Snow White appearance of the upstream side of the sensors. You can even see little dots...which looks like it came through the cat like that. I think it's doubtful that the white stuff is coolant. The material actually felt like a grease or antisieze when I removed it. My assumption is that it was either ceratec or one of the pea fuel additives I just recently used, and Im leaning towards ceratec. Im glad to have the new oils that we use (sp) so I dont wonder about any of the additives or helpers anymore.
Anyone ever have a random stud break on their m157. Think warranty would cover that?
Last edited by Baltistyle; Aug 8, 2025 at 08:16 PM.
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I did this without removing any exhaust components and jammed my hands up in there for the connectors…not pleasant. The sensors came out no problem with a proper o2 wrench and a flex head ratchet, all from underneath, on a jack and jackstands.
