John@Motorcepts

I only use Shell VPower for my cars. U shouldnt use fuel less than 91 octane when u can get it since the ECU recognizes it and will try to make up for the less octane by timing etc. It's safer to use 91+ since the ECU is tuned for it in the first place. If the car requires 87, why r u going to put 91/93? it's useless and doesnt give u more power but when the engine asks for it, give it.

I have a Shell credit card which gives me 5% rebate every time. Plus, some gas stations charge u extra for using a credit card but if I am using a Shell CC in a Shell gas station, I dont get charged extra AND I save.

xcntrk

The answer is simple; as long as you don't detonate you can run whatever octane fuel you want.


BMW knock detection operates the same as any other vehicle manufacture. There's a knock sensor attached to the block that monitors engine noise and feeds that data to the ECU for interpretation. The ECU operates an algorithm to match that engine noise data against a threshold and when it's exceeded knock is present and action is taken. Here's a good description of BMW's knock sensors from a supplier:
http://www.partstrain.com/ShopByDepa...r/BMW/5_SERIES

2exclusive

how would you know when your knock sensor doesnt work?

xcntrk

I believe there's a CEL or DTC for knock sensor failure.

or_550i

when the dual knock sensors (M45) and quad knock sensors (N62) fail an error is stored in the DME. In the event of a failure of a knock sensor the DME uses a constant retard setting that is based off of the ignition timing.

The error is DTC (OBD-II). The error should also indicate which knock sensor bank failed.

or_550i

Unless you hear knocking after using < RON 91 there is not much to worry about. Prolonged knocking will result in engine damage.
There are a few things that increase the changes of knocking [in the e60]:
Increased compression ratio
high cylinder charge
poor fuel quality
high intake/engine temperatures

Octane rating is only one of a few other things that can cause knocking. Unless you manage to do all of those at once, the chances of knocking are small.

Sort of. The DME is 'mapped' to expect it.

"pre-detonation" here with regard to knocking is a few milliseconds - not much longer. The fuel is not going to explode the instant it enters the cylinder.

The only times I have ever heard of seen engine damage was on tuners and old cars that do not have electronically controlled injection and timing.

Yes. From the BMW Knock Sensor description...
If knocking occurs, the ignition is retarded for a certain number of working cycles and then gradually approaches the original value. The retard setting can be controlled individually for each cylinder bank (cylinder bank selective).

The DME does not avoid knocking it just reacts to the knocking to prevent further knocks. Keep in mind that it can detect a knock on an individual cylinder bank and react within a few revs - all of which happens so fast that you probably never hear a knock.

As xcntrk has said, quite correctly, using 87 would be fine and would not result in any problems - just a loss of performance.

If you really want to know what a knock sounds like... Get in 4 cylinder Honda. Put in the lowest grade fuel you can find. Load it with as much heavy stuff you can fit in it. Drive up a steep hill. Floor it. That's a knocking sound you will never hear in a BMW even with 87.

xcntrk

Not that I would advise that. If the manufacture says premium, then use premium.

rafichicago

Exactly. Car is too much of an expensive toy to experiment with. I think BMW engineers are more knowledgable than most of us to risk not doing what they say.

pinguhk

well some time I don't trust the manufacture.
they also say you never need to change the gearbox oil and filter.
I did it and the oil inside was think and black with loads of metal dust inside.

KREATE