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Discussion Starter #21
How many variables affect the fuel trim value? I thought it was only the upstream sensors that did that but it would be interesting if there were more that I could check.

As to your point about the vacuum leak Yes I did remove the intake recently. I was very careful to get the gaskets back correctly, and The upstream on bank 1 is reading a rich condition over high and low rpm which does not support the idea of a vacuum leak.
I think I bit off more than I can chew and Im considering givong it to the pros to diagnose it.
 

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Discussion Starter #22
Ok I found out today that the diagnosis sensor on bank 1 b1s2 that I changed a week ago is actually the wrong one. I got the b1s3 sensor by mistake.
Could this affect fuel trims? I thought only the wide band sensors before the cat affected fuel trims. If it does that would explain a thing or two bc it is reading lean.
 

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2003 330cic, 2003 325iT
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2003 330cic, 2003 325iT
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How many variables affect the fuel trim value? I thought it was only the upstream sensors that did that but it would be interesting if there were more that I could check.

As to your point about the vacuum leak Yes I did remove the intake recently. I was very careful to get the gaskets back correctly, and The upstream on bank 1 is reading a rich condition over high and low rpm which does not support the idea of a vacuum leak.
I think I bit off more than I can chew and Im considering giving it to the pros to diagnose it.
The sensors in our cars that are used for fuel trim are the MAF, the temperature sensor (I believe) and the pre-cat O2 sensors. Pre-cats are used to evaluate combustion efficiency relative to airflow and the fuel system is adjusted.

Systems that tend to affect fuel trims (negative at least) are fuel pump and filter (under-delivery confuses the ECU), vacuum/CVV (leaks after MAF also confuse), and pre-cats (under-reporting/lazy sensors give the wrong data back to the ECU.

Rich conditions can be caused by injectors, cats, etc.

We may be in a rabbit hole on the o2 sensors. How old are your precats, your pump and filter, and your MAF (in miles)?
 

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Discussion Starter #25
The sensors in our cars that are used for fuel trim are the MAF, the temperature sensor (I believe) and the pre-cat O2 sensors. Pre-cats are used to evaluate combustion efficiency relative to airflow and the fuel system is adjusted.

Systems that tend to affect fuel trims (negative at least) are fuel pump and filter (under-delivery confuses the ECU), vacuum/CVV (leaks after MAF also confuse), and pre-cats (under-reporting/lazy sensors give the wrong data back to the ECU.

Rich conditions can be caused by injectors, cats, etc.

We may be in a rabbit hole on the o2 sensors. How old are your precats, your pump and filter, and your MAF (in miles)?
Hahaha. I know about the damn cats and sensors. Waaay too many for its own good. Its from 2002 but it had all cutting edge tech back then. And now its acting up.

Precats are about 90 000 miles, I changed them after replacing oil stem seals bc I had a effeciwncy code and suspected that the leaking oil had damaged the cats.
Both the MAF and fuel pump are probably 160 000 miles bc I suspect they have never been changed.
Fuel filter and fuel pressure regulator I changed about two years ago so they should be ok. Fuel pressure regulator vacuum hose is new I changed it just weeks ago. Double checked all fittings.
The injectors do not leak but I have not checked the pressure at ignition and idle. I want to do it but I am trying to find a resonably price gauge.

Thanks for your input. Very good info about the fuel trims. The MAF is suspect, and fuel pressure as well. The maf is not very expensive, about 70 usd over here.
 

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Discussion Starter #27
Okay I found something. A note from about 3 months ago where I put down the fuel trims at the time.
They are way more reasonable then the values I have today, LTFT B1 - 3% and B2 - 1%.
It seems that whatever is going on now I caused myself by changing parts. I will have to backtrack my steps to figure it out.
I changed the B1S1 to a used one, bc Im cheap and wide band sensors are very expensive. I did it bc I guessed it might be causing the cat inefficiency code. The other sensor I changed was B1S2 which I now was the wrong one and another one is in the mail.
Im going to change these parts again to see if it fixes the problem.
Thanks for the help guys, unfortunately it might all have been my mistakes.
Ill post back in a few weeks after changing the parts again.
 

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Discussion Starter #28
Okay update on the old 318i.
Today I changed the B1S2 diagnostic sensor on after the pre-cat on bank 1. All values returned to normal after this change. A week ago as I said I installed the wrong B1S2 sensor by mistake, the part nr was only off by one number thats why I didnt spot it at first. I noticed however after driving a while that the B1S2 sensor (narrow band) was reading 0,0 v most of the time which means lean condition, and the B1 LTFT went up to +5,5%. That's when I started this thread to ask for help. I was confused bc I did not suspect that the B1S2 sensor affects fuel trim, IT DOES.
It's the only variable that I have changed after getting the weird readings and now values are back to normal, and both banks reading LTFT -2,3% which is pretty normal. I will post pics here so you can see for yourselves.
The values are pretty consistent over revs as well which indicates no vacuum leaks.

I want to thank everyone who tried to help me solve this. Hope you are staying safe during these times. We'll talk again when I mess up next time I presume.

906969
 
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