System too Lean Bank 1 and 2 - 4.6 V8

Been noticing a little hesitation in some rev ranges so decided to put the code reader on the car.

Had 3 codes stored.

System too Lean Bank 1

System too Lean Bank 2

And there was also a code which I did not read fully which mentioned O2 sensor. However that code has cleared itself.

Now I have done a little research and it may point to the MAF sensor, so I will clean this very carefully with some electrical contact cleaner. The MAF looks very similar to that on a BMW E46 M3 which I used to own, I cleaned the MAF in the M3 with contact cleaner and the difference made to the throttle response was quite noticeable.

Other research points to a possible vacuum leak, so I will check all pipes and connections.

However, I feel there maybe a problem with the ECU giving enough fuel if the O2 sensor/s are not working as they should.

What are your thoughts?

Sounds like you're on the right track. I've used carb/injector cleaner rather than contact cleaner on the MAF and have the impression that it got quite a bit of crud out. Just a thought.

Had similar fault a while back, had this advice given to me "you can test it by running your car till warm then unplug it and take it for a drive. don't leave it unplugged as it will not start from cold" "when you first unplug it runs poorly for a few min then should clear up"> If all your symptoms disappear then it is the maff so clean or replace it, the only other thing is apparently you have to reset the adaptive values after you have replaced the maff but how important this is I am not sure.

Hope this helps

resetting ecu adaptive trims is a 'short-cut' but well worth it. the car will start learning the new trims even without it but could take many hundreds of mile depending on how much data its already stored and that its trying to average. resetting it is like setting your trip computer to zero and checking average speed or fuel consumption after 10 miles. Much more relevant to how the car is actually being driven now as compared to how its been driven over time.

most people suggest resetting ecu trims whenever any work is done on the induction side or if any major sensors such as intake temp sensor or O2 sensors etc have been changed.

As the O2 sensor is the sniffer in the exhaust it is reading the unburnt fuel or lean mixture with the faults you have I would be inclined to check the maf reading as it could be that at fault or you have a air leak after the maf

Thanks for the advice.

I have been experimenting with the MAF sensor being connected and then disconnected.

The car seems to be better with it disconnected, however it is only a mild improvement, the revs still seem to be struggling to rise with it disconnected.

I will replace the MAF as it could be funked.

I am having a new exhaust put on this Friday so I might as well get the Lamda's changed while they are there.

There are four of them, am I correct one before each cat and one after?

I have not had a chance to check for air leaks but will spend some time on this before the weekend.

Does anyone have any experience with K & N cone filters for the THOR P38, from what I have read there is only a panel filter available for that engine.

Thanks again for your help

Dont waste money,(And precious metals) on replacing the Oxy sensors.Your car sounds like a classic case of a failing Maf.When they fail they tend to give a lower than normal reading,because of this for a given airflow reading the ecu will only give a low maximum injector pulse width.this results in a lean mixture,poor performance and fault codes stating Oxygen sensor problems in switching rich.resetting the adaptive values before changing a low reading maf will only make matters worse as the adaptions will already be at their max positive value.Resetting will just narrow down injector pulse width even more - resulting in an even leaner mixture,possibly to the point of being undrivable.
ideally it should be tested on Testbook looking for a reading of 22-25KG/hr at idle and more than 90KG at 3000rpm running free,engine hot all loads off.

eightinavee said:

Dont waste money,(And precious metals) on replacing the Oxy sensors.Your car sounds like a classic case of a failing Maf.When they fail they tend to give a lower than normal reading,because of this for a given airflow reading the ecu will only give a low maximum injector pulse width.this results in a lean mixture,poor performance and fault codes stating Oxygen sensor problems in switching rich.resetting the adaptive values before changing a low reading maf will only make matters worse as the adaptions will already be at their max positive value.Resetting will just narrow down injector pulse width even more - resulting in an even leaner mixture,possibly to the point of being undrivable.
ideally it should be tested on Testbook looking for a reading of 22-25KG/hr at idle and more than 90KG at 3000rpm running free,engine hot all loads off.

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Thank you for your valued and knowledgeable input.

I will now just change the MAF on the basis of this and see what improvements are made.

I assume that a simple disconnection of the battery for a few hours is not enough to reset the adaptive values?

On my E46 M3 the car had to be connected to DIS/GT1 to have the adaptations reset.

If the maf is whats wrong,(You ought to have it checked really,on live data) then the engine ecu will quickly see the higher reading and trim to it.Disconnecting the battery wont reset the long term adaptions,but I wouldnt worry too much about them anyway.

eightinavee said:

looking for a reading of 22-25KG/hr at idle and more than 90KG at 3000rpm running free,engine hot all loads off.

Click to expand...

top post Eight, thanks for those numbers. they're going into the margin of my owner's manual (said margin is starting to get a bit crowded!).