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Hello sir, love your videos and have been a sub since day 1.
Had a question for you. I have a bmw z3 with lean codes. Car has extensive service history. Had it for 12 years.
To diagnose the problem i smoked it, no leaks.
I watched your video on fuel trims and my situation is very odd.
Trouble codes are p071 p074-lean bank 1 and 2.
Short term FT are 10 -12 for bank 1 and 2
Long term fuel trims are 11.7 for both banks. And they stay 11.7 with rpm at 2.5k.
Interesting thing is short term fuel trims go up to bank 1/2 to + 12/17 respectively with rpms going up to 2.5k
O2 sensors. I’m getting normal reading for both bank 1 pre and post cat sensors.
Bank 2 o2 sensors stay at .8 value no matter the rpm
I’m really confused.
I smoked the car with professional smoke machine, no leaks
I was getting negative short term fuel trims but cleaned MAF and now I’m getting positive as per explained above
In conclusion LTFT are stuck at 11.7
STFT are positive at idle and climbing with throttle opening and high RPM.
When I’m driving in 4-5th gear as I accelerate fuel trims climb up and when I let go of the gas pedal they abruptly go to 0.
Worsening fuel trims with higher rpm suggest a fuel delivery probplem. Check fuel pressure and fuel volume? You may want to observe the front O2 readings while full throttling the engine while in gear. The readings should go full rich with an appropriate fuel supply. If ithey don't go full rich you have an issue.
Stepping completely off the gas pedal will enter the decelaration mode, no fuel is supplied hence a 0 reading.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Why would you make out of both bank 2 o2 sensors reading constantly high voltage of approximately.7 to .8?
Would that suggest that the fuel delivery problem is in the second bank?
What re the likely findings of the fuel system test.
Loss of pressure so bad fuel pump or fuel pressure regulator or clogged injector.
Would you think it is a good idea to switch the o2 sensors around and see if the high voltage read in bank 2 sensors follows? In my opinion it is unlikely both bank 2 sensors be faulty at the same time.
Thank you for the reply. And this is a revision of the unclear previous message.
What would you make out of my finding that includes both bank 2 o2 sensors reading constantly high voltage of approximately.7 to .8 regardless of the speed.
Would the abnormal O2 sensor readings in Bank 2 suggest that the fuel delivery problem is in the second bank of my engine?
Also, I have in mind that the STFT and LTFT are the same for both banks. This is a straight 6 cyl engine.
What do you think are the likely findings of the fuel system test that I will find?
Do you think it will be bad fuel pump or fuel pressure regulator or clogged injector.
Would you think it is a good idea to switch the o2 sensors around and see if the high voltage read in bank 2 sensors follows in bank 1? In my opinion it is unlikely both bank 2 sensors be faulty at the same time.
common problem with crankcase vent valve, when engine is warm and at idle you should have a slight crankcase vacuum of 16 mBar. also, the cyclone oil separator had a hose that connects to the oil dipstick tube, that would rot and cause leaks also.
normally you check vacuum with special oil cap, or you could remove the oil dip stick and measure from the pipe.
common problem with crankcase vent valve, when engine is warm and at idle you should have a crankcase vacuum of 16 mBar. also, the cyclone oil separator had a hose that connects to the oil dipstick tube, that would rot and cause leaks also.
normally you check vacuum with special oil cap, or you could remove the oil dip stick and measure from the pipe.
The manifold has been removed, resealed and smoked with no vacuum leaks. The oil separator Ccv pcv valve has been replaced along with the hoses.
The STFT go up with acceleration
O2 sensors for bank 2 are recording .7 and .8
I do not have the special vacuum measuring oil cap but I did the test where you try to remove the oil cap while the engine is running and there is some vacuum but not a lot where it is difficult to remove the oil cap.
Do you experience any driveability issues or higher than normal fuel consumption? Do both downstream O2 sensors read .7 - .8 volts. Do these reading drop when stepping off the pedal? Do the upstream O2 sensors react to an introduced vacuum leak?
Please provide data.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
There are no drive ability issues. Car pulls hard and does not hesitate in idle or acceleration in gear.
Fuel consumption could be a bit high yet but I wouldn’t have any way to measure.
Failed to mention that the car has been sitting for 6 months since I moved and had it transported from the East to the west coast. All the extensive maintenance has been performed in the past and the car was fine since until it sat.
To be clear both bank 2 o2 sensors ( upstream and downstream) are the ones that are giving the .7 to .8 volt reading under any condition. Idle or acceleration and cruise speed.
The bank 1 pre and post cat sensors are acting normally fluctuating from .1 to .9
I will report on the last question whether the bank 2 o2 sensors react to a vacuum leak.
Thank you for the reply! Yes will do, got a fuel system pressure tester from autozone but doesn’t fit my application. So I have to wait. I will report my findings!
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