S54 running (slightly) rich

[Arclitgold]

I’m dealing with this exact same issue. However I have reason to believe that my cats may be also going bad.

I’m planning on getting all o2 sensors replaced, and then remeasuring the o2 voltages as it appears my Bank 2 post cat voltage is fluctuating at the same rate as my pre-cat.

[Slideways]

I’m dealing with this exact same issue. However I have reason to believe that my cats may be also going bad.

I’m planning on getting all o2 sensors replaced, and then remeasuring the o2 voltages as it appears my Bank 2 post cat voltage is fluctuating at the same rate as my pre-cat.

When the post sensor voltage follows the pre sensor voltage, that does indicate a bad cat. As long as you do not have O2 sensor codes, the sensors should be working correctly.

BMW does suggest 100k mile service interval for O2 sensors.

[BL92]

1 of post cat 02's is dead, i do not think that effects LTFT

I have a slight stumble at start up from time to time, i am thinking injectors are shot

[ATB88]

Back on the old forum pre-2020 I had some long thread about chasing lean LTFTs and seemingly less than ideal fuel economy, threw basically every part one could throw at the car, it never changed anything. I wonder to what extent LTFTs on some engines are the way they are simply due to manufacturing tolerances on the heads, valves, etc?

Car's modified and tuned now (whereas was bone stock back when I was chasing this down), so I figure it's not really meaningful to compare current LTFTs to the ones that I was trying to fix before.

I kind of wish my old thread still existed to try and dissuade anyone from getting too obsessed with fixing this. Then again, if people are able to make discoveries about how to diagnose these issues that I missed, I'm interested in seeing it happen!

[Shonky]

No updates from me. I just live with it. Car is a weekender at best. It runs perfectly, pulls well, doesn't audibly ping. I don't have an idea of fuel economy but it's not drastically bad.

Back on the old forum pre-2020 I had some long thread about chasing lean LTFTs and seemingly less than ideal fuel economy, threw basically every part one could throw at the car, it never changed anything. I wonder to what extent LTFTs on some engines are the way they are simply due to manufacturing tolerances on the heads, valves, etc?

These are really "rich" LTFTs. DME is reducing the amount of fuel because it think it's too rich.

Injectors was probably a next guess for me, but given it doesn't really seem a problem, I'm hesitant to chuck money at it.

[sapote]

I don't have any fix, no.

I did throw a brand new Bosch MAF from FCP as I was doing an order at the time. That did not fix it and I'd have to check the numbers but it ended up about a percentage point worse than I had before. ie slightly richer again. Im still running that new MAF after many months. I might revert to the old one without a clear and see if the values come up a small amount.

The MAF graph below looks so wrong with very high value in g/s at idle. I like to see the MAF data at hot idle, should be less than 5g/s

[sapote]

I wonder to what extent LTFTs on some engines are the way they are simply due to manufacturing tolerances on the heads, valves, etc?

Car's modified and tuned now (whereas was bone stock back when I was chasing this down), so I figure it's not really meaningful to compare current LTFTs to the ones that I was trying to fix before.

With proper parts installed, even a modified engine should have proper LTFT as the DME continues to adjust the injected fuel for a proper pre-cat o2 reading.

Post the hot idle data of pre-cat O2, MAF, rpm, engine temperature and I will tell what's going wrong/right. Better to use OBDFusion app and upload the csv file to datazap.me for graphing the data, then post your datazap link here.

Edited: datazap.me, not datazap.net

[Shonky]

The MAF graph below looks so wrong with very high value in g/s at idle. I like to see the MAF data at hot idle, should be less than 5g/s

This was a long time ago. It wasn't all idle. There's no way you can read the g/s at idle because of the graph scaling.

From memory it is high 4.xx g/sec at warmed up idle.

With proper parts installed, even a modified engine should have proper LTFT as the DME continues to adjust the injected fuel for a proper pre-cat o2 reading.

Post the hot idle data of pre-cat O2, MAF, rpm, engine temperature and I will tell what's going wrong/right. Better to use OBDFusion app and upload the csv file to datazap.net for graphing the data, then post your datazap link here.

I will do this in the new year and await your diagnostic skills.

[Arclitgold]

I’m looking forward to see what comes of this!

[BL92]

Same ! Thanks for the updates, hope more memebers chime in with there LTFT from inpa on my other thread so we can all compare
Who has widebands installed? can anyone post AFR figures for us ?

Anyone else with rich LTFT got the cough at start up ?

few sellers on eBay throwing injectors around

What about logging with testo ?

[Shonky]

Anyone else with rich LTFT got the cough at start up ?

Mine starts "on the button" every time.

Previously it did occasionally not fire first time seemingly regardless of crank time. I'd stop cranking after a second or two (long enough to know it probably wouldn't fire), cycle key and second time would be instant. I don't know what fixed it but it *seemed* to go away around the time I did the VANOS. There wasn't anything wrong and it passed the DIS test prior, I just did the Beisan kit. I've seen the odd report of similar but no explanation.

[Arclitgold]

Other than the P0430 code I’m getting, and the similar LTFT numbers, my car runs like a top. Go figure…

[sapote]

Other than the P0430 code I’m getting, and the similar LTFT numbers, my car runs like a top. Go figure…

Low cat efficiency will fail smog check; what is your plan for passing smog?

Post the datazap.me link here and we will take a look of what's going wrong.