knocking on 89 gas

Guys, I've been running 89 in my car since I bought it. Rattles somewhat depending on throttle. I have done just about every tune up item possible. Plugs, CCV system, O2's, cooling system, fuel filter, DISA valve. What else in gods name can be causing it? I thought the car has a Knock sensor and 89 under "normal" conditions would be ok. If I run 93 it goes away. I know the answer I'm going to get... run 91+. but a stock car like this under a watchful eye and in great shape should run on 89 w/out rattle. Is my Knock sensor bad? No CEL.

Its tuned to run 91+ by running 89 it will probably have knock. The guys at BMW know what their doing. They tuned it for 91+ because they can get more power from it. If you really MUST run 89, you could try calling dinan or another tuning company and get it tuned for 89. The cost for manufactured tunes from them are 300+, so if you are trying to save costs it will be cheaper to run 91 than to keep modding to try to get it to run 89. If you live in a place where 91 is not available, might still be cheaper to buy your own gas tank and have 91 delivered to your driveway.

What does the gas cap say? There s/b a minimum octane listed.

my boss doesn't like paying for 91. When I'm "persoanlly" driving 93. business 89. I've run my 335i on 89. no knock. I just don't romp it.

try kerosin
its cheaper

Not sure what the I-6 comppresion ratio is but im assumming its around the same as the V-8's. With a 10:1 compression ratio you need to run Super unleaded, or add an octane booster/anti knock additive.

Pay for the difference when using it for business. It's your car after all. The difference should be about $5 ea tank.

Something's wrong w/ your car if you can't run 87 oct. w/o it knocking.
My car runs perfectly fine on regular gas 87 oct.

i think you're right w/ suspecting that your knock sensor is not working right.
It's supposed to detect knock and send a signal to the computer so the computer can retard the ignition to prevent knocking.

The difference in price per gallon around here is .20 cents, at most. On a 15 gallon fill-up -- that's $3. On top of a $50 transaction.

My car runs much better on Super. You might be able to get away with 89 octane in warmer weather, but is it worth it ?

I run Super and don't think twice about.

I still think there is something wrong with the knock sensor on 89. 87, ok fine.. yeah. but 89? eh... something is not right.

Have you tried different brands of fuel?

Ditto. I run 89 in (3) e39's year round without any difficulty or any audible knocking.
Perhaps noises are VANOS or exhaust rattle.

Originally Posted by DHoang

Something's wrong w/ your car if you can't run 87 oct. w/o it knocking.
My car runs perfectly fine on regular gas 87 oct.

i think you're right w/ suspecting that your knock sensor is not working right.
It's supposed to detect knock and send a signal to the computer so the computer can retard the ignition to prevent knocking.

Originally Posted by FLE39

Guys, I've been running 89 in my car since I bought it. Rattles somewhat depending on throttle. I have done just about every tune up item possible. Plugs, CCV system, O2's, cooling system, fuel filter, DISA valve. What else in gods name can be causing it? I thought the car has a Knock sensor and 89 under "normal" conditions would be ok. If I run 93 it goes away. I know the answer I'm going to get... run 91+. but a stock car like this under a watchful eye and in great shape should run on 89 w/out rattle. Is my Knock sensor bad? No CEL.

When I had a vacuum leak, it made the car knock. Check all hoses. Mine was the hoses that came off of the MAF boot and went to the front of the intake. There are like 3 hoses there.

Originally Posted by FLE39

I still think there is something wrong with the knock sensor on 89. 87, ok fine.. yeah. but 89? eh... something is not right.

a bad MAF could cause this too.

Originally Posted by ninetyseven1

a bad MAF could cause this too.

Unplug the MAF and drive it and see if you still hear knocks. Keep in mind though that when coming to a stop your car could stall out with a disconnected MAF sensor. Also, your traction control will not function.

Originally Posted by ninetyseven1

Unplug the MAF and drive it and see if you still hear knocks. Keep in mind though that when coming to a stop your car could stall out with a disconnected MAF sensor. Also, your traction control will not function.

Also, the knock sensor wiring corrodes. I unplugged one of mine from the black electrical box on the intake and looked inside the connector. There are four small wires inside the actual connector plug. I had 2 wires that were touching! The actual plastic insulation around the wires just plain corroded off! You will have to split the rubber boot on the connector plug with a razor blade to see inside it. Just tape it back up with electrical tape. It's worth a shot.

No vacuum leaks. I replaced all the vacuum hoses and MAF boots. I also spray carb cleaner around items with the engine idling (cold!) to verify. I need to look at the wiring going to the knock sensor. It's not VANOS noise... or exhaust. it's spark knock. I'm 100% sure. I know what it sounds like. I've been driving modified cars for 13yrs. Sounds the same in a V8 as it does in a TT Supra, as it dones in a junky Malibu. It's spark knock. But this new of a car (yes 2003 new) should adjust for 89 gas. Brands do not matter. I drive about 30-40k year. I get to try brands all over the Southeast. How many knock sensors does the M54 engine have? 1 or 2? Approx where is it?

Why doesn't your boss do like most companies and reimburse you per mile? Ala, $.55/mile to cover your gas, insurance, vehicle maintenance, and wear.

^I've done that too. It's a deal thing I have worked out. The car should run fine on 89 as long as I'm not romping it. my 335i does and it's TT. I need to at least make sure the knock sensor is good and the wiring is not shot.

Originally Posted by FLE39

^I've done that too. It's a deal thing I have worked out. The car should run fine on 89 as long as I'm not romping it. my 335i does and it's TT. I need to at least make sure the knock sensor is good and the wiring is not shot.

check th knock sensor wiring,it's prob not maf wiring

Originally Posted by FLE39

^I've done that too. It's a deal thing I have worked out. The car should run fine on 89 as long as I'm not romping it. my 335i does and it's TT. I need to at least make sure the knock sensor is good and the wiring is not shot.

I will never understand; especially on an FI car.