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hello. just purchased a 95 740i a week ago. i bought it with the check engine light on. i knew the oil hadn't been changed. the engine runs great though. i made sure i fill it up with premium gas. added stp gas treatment. check engine light went off today.point is make sure u use premium gas. next is ac. compressor blows. a little cool at night. if not a leak,i'll ad freon.if so, i can get one really cheap. these cars are not that expensive to maintain. long as the engine and transmission are fine u can replace parts really cheap. just buy used parts. owned a mercedes diesel and didn't have any repair issues. so it's a myth about maintenance unless u want to pay the dealer.
 

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definately use premium fuel, the E38, or really any other BMW is tuned to use specifically high octane fuel only to prevent knock. this is why the check engine light will come on, because the knock sensor picks up predetination knock. you may not even hear or feel it, especially if the car is in top running condition.
 

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Amen about the premium fuel... my 740 didn't get 5km down the road before she knew I cheaped out on the fuel grade! I had to run premium for a week and reset the computer before that light went out again! Learned my lesson.
 

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I am no expert, but several experts have told me to never use any additives but BG. You can buy them on line cheep. Of course use best fuel available w/o Ethonol!
 

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i have a 1995 740 il and i run mine on 89 octane and she still runs beautifully i get better miles with premium but as long as your not using regular unleaded you shouldnt have a problem the cheaper the gas the more dirt deposits in it. the worse it runs pay for quality and youll get it if thats not the case than there is probably something else wrong
 

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The manual on my 97 says anything above 87 octane will work. 85 flex fuel should not be used, and 100+ octane racing fuels sometimes contain lead which will destroy cats and O2 sensors, so they should not be used either.

There is no such thing as mid-grade, and when you select mid-grade at the gas station, the pump will give you a 50/50 mix of regular and premium. There are only two underground tanks that hold gasoline at gas stations, regular and premium.

Premium would be best as it does not contain ethanol and it is what the motor was designed to run on. Lower octane fuel will cause the knock sensors to retard timing and cause your car to lose performance and gas milage, but when knock sensors get old, they detect false knock and could be doing this anyway, even if you use premium, and in that case, lower octane fuel wouldn't make a difference.

So, choose whichever one you think is best under your circumstances.
 

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I was using 89 for a few months; then i changed my oil. my german mech said what grade of gas are you using:thumbdwn:

dont know how he knew. use only 93. PLEASE FOR THE SAKE OF YOUR ENGINE:)
 

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I've been running my baby on 89 octane and its still a beast!
Well you should switch for 91 or even higher if is available, to see what the real beast can do.
And also if you really love your bimmer and you want to keep it for a while you should switch to 91 at least. Ethanol in the gas damages fuel rubbers in time and produce rust in your fuel tank .
I don't see any advantage of the 89 other than cheap. The 91 gives you a better gas mileage . If you do the math you will see that you save nothing and the car does not perform so good as it does with 91. Even the 95 year/model has been build for 91 octane.
Good Luck!
 

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Hi everybody, I'm new to this forum and I do not like in states, here we have 91, 95 and 98 which I believe 91 is the same as your 89. I have noticed that I'm getting horrible gas millage around 420Km will full tank , something between 19 to 22 litre per Km ( please excuse my different measuring system ) , i have asked this in other beamer forums and i thought there no harm asking here too.
in last two months, I have replaced intake manifold, rocker cover gasket, MAF ( not original ), o2 sensors ( original ), fuel filter, plugs, oil filter, air filter ( all after market ) and still suffering this problem.
my last scan shows ( activation cooling map and knock sensor 3 and 4 error )
Need your help please, any idea would be appreciated. I may need to remove this and make it as a thread.
 

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If you have knock sensors related codes combined with pour gas millage, switch to a higher octane fuel. If not available try to add an octane booster additive. The knock sensor will detect the detonation time and will retard timing. With another words they will detect what fuel you are using and let computer know about it. If you have only on one bank (3 and 4 cyl.) you might have a breakage in the cable. Both sensors are wired together. I am assuming that you are having the V8 engine.
Here the 89 octane contains 10% ethanol. My gas millage is around 22-23mpg(10.23/100km) out of town and 17(13.84l/100km) in town. This when my wife is driving or when I am very kind with it.
 

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If you have knock sensors related codes combined with pour gas millage, switch to a higher octane fuel. If not available try to add an octane booster additive. The knock sensor will detect the detonation time and will retard timing. With another words they will detect what fuel you are using and let computer know about it. If you have only on one bank (3 and 4 cyl.) you might have a breakage in the cable. Both sensors are wired together. I am assuming that you are having the V8 engine.
Here the 89 octane contains 10% ethanol. My gas millage is around 22-23mpg(10.23/100km) out of town and 17(13.84l/100km) in town. This when my wife is driving or when I am very kind with it.
Thank you very much, very informative, I will try higher octane next time and yes it is a V8, i will have a look at the cable on weekend, hopefully doesn't need to remove manifold.
 

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that means 0.12 mpg. :yikes:

Are you sure about these numbers? use the conversion in here http://www.convertworld.com/en/fuel-consumption/Liters+per+km.html
Hi, sorry , it uses 19-21 liter per 100KM (21L/100Km), you are right, however when I compare your gas consumption, it is still way way less than mine. :bawling: , my car used to be like yours,however for some odd odd reason, since I got it back from full service, it is doing this and the mechanic said that they haven't done anything to upset the car. Maybe they were pissed of cos I supplied the parts.
 

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Aftermarket parts (like filters) shouldn't influence the gas consumption in such a bad way. MAF it might influence a bad gas consumption, but it should pop out some error codes as well (MAF related).
 

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Aftermarket parts (like filters) shouldn't influence the gas consumption in such a bad way. MAF it might influence a bad gas consumption, but it should pop out some error codes as well (MAF related).
True, I replaced the MAF too, beside the high usage, every thing is ok, engine is very smooth, except in low RPM on high gear RPM seems to going up and down noticeably which i was advised it is a tranny issue and needs to change the fluid and filter. It also giving me activation cooling map which I believe is thermostat related issue, I checked all the connection, looks good. gas price here is more than $2.10 per liter which is killing us at the moment .
 
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