BMW 4.6 is poor acceleration and hesitation

[Aman]

Originally Posted by bcredliner

I think you are right not to consider the emission test

O2 sensors, especially the pre cat sensors, should be replaced at 60-70,000 miles to assure your mileage and/or performance doesn't take a hit. I still think you should have them tested before purchasing sensors but even before they go bad the performance declines and can be an intermittent or continuous decline to point of failure.

Okay I may just change them as you suggested
Are the pre cat sensors and connectors easy to get to?
Is it ok to use ngk/ntk replacement sensors?
Is is possible a faulty sensor could create a code 26 or 29 fuel trim limit reached scenario?
Cheers

[bcredliner]

Sometimes the sensor is tough, depends how much corrosion. Other than that it is easy. I suggest using a sensor removal socket, makes it much easier, especially if it is a tough one.

Use OEM or OE sensor only.

Yes, those codes can be caused by o2 sensor. Test them first!

[Aman]

So haven't been driving car much
Today finally got round to testing O2 sensors
On a graph (at 2000rpm), precat sensor bank 1 is going up and down regularly, and sensor bank 2 also goes up and down regularly most of the time, but sometimes the time it takes to go up and down increases, so there is more delay between max/min (frequency decreases)
So hopefully tomorrow will get these changed

[Aman]

Update:
Changed left and right pre cat O2 sensors with bosch ones
Car seemed more powerful and exhaust emissions seem a lot less smelly
Later in the day the engine light came on and stayed on (after O2 sensor change)
Previously when this happened the power to the engine was reduced
This time the power to the engine is the same as before the engine light came on
The only other code coming up was for the electronic thermostat
As I was dealing with the O2 sensors I haven't investigated thermostat yet
Will faulty electronic thermostat bring up check engine light or will it just store a code
The water temperature on the dash is in the middle of the gauge
Is the dash sensor the same as the electronic thermostat sensor or is it a different sensor?
Will a faulty electronic thermostat affect the performance of the car? (even though dash water temperature is always normal)
(Will get car codes checked again when I have a chance, but just thought I'd ask for now)
Thanks

[TerminatorX5]

thermostat controls temperaturte of the engine, it opens to send coolant on big loop, closes to keep coolangt on small loop - if it is stuck in one position, the best is when it is stuck in open position, when the coolant goes on big loop, thus the engine is not overheating but rather stays below operating temperature, which is bad too, just not as catastrophic... the thermostat does not measure temperature, it only opens and closes based on the measurements taken by the temperature sensors... there is one sensor unit with two sensors built-in, one sensor actually sends the info to the engine and the other sensor sends the info to the cluster... in absense of the correct sensor readings, the computer substitutes the temperature value based on other temperature readings (air, oil, etc) but it is not a good option, as the performance is reduced/compromized... you might not feel difference in newly found performance but you might only lose 1-3 horsepower, so to say...

as far as the check engine light, best to read the codes and see what it says, as the light comes on for various reasons...

[Aman]

Hi again
Checked the codes
Catalytic converter code bank 2 is NO longer there
But I have code 26 multiple fuel trim bank 1 limit exceeded
Any ideas what this could be?
MAF is new, pre cat O2 sensors are new
Is it necessary to reset adaptions after putting new O2 sensors in?
(I didn't do that)
Thanks for any help you can give

[Aman]

Update:
Engine light was reset and has not come back so far
Car is running better every day since oxygen sensors have been changed
No fuel trim fault codes so far over last 60 miles / 100km
I guess perhaps car has to re-learn mixture settings, which were probably way off due to old sensors

[Aman]

Over a week now since last engine light was last reset:
Still no check engine light coming back on
It actually feels as if each day the car is becoming faster and smoother and the exhaust gasses don't smell of much now.
Less and less pedal effort is required to make car move now
Hopefully it will become more economical too !
Can't believe I was putting up with them smelling so rich before oxygen sensors were changed, as several of you advised me to.

[Aman]

Hi does anyone know if these fuel trim values are normal (at idle)
The long term bank 1 stays at +3 to +8%, but long term bank 2 is -1.5 to +1.5%, and averages 0.
When I open the throttle fully, long term bank 1 goes (down) to approx 0.8%, but long term bank 2 (goes up) to approx 3%
The reason why I ask is because although car has improved since replacing catalytic converters (bank 2 was damaged), and after replacing both pre cat oxygen sensors the car definitely improved more.
But what I'm finding now is that the car is much more powerful than before, but sometimes it has loads of effortless acceleration and sometimes it needs to be pushed and acceleration doesn't feel as smooth or rapid.
What I have recently noticed is that sometimes car idles at approx 710rpm slightly rough, and sometimes it idles at 600rpm smoothly (i always check idle with all accessories off and car warmed up)
Any ideas what could be wrong?

[Aman]

After going on the motorway for 80 miles, most of the time on cruise control (this makes it go into closed loop, right?)