Gas Question

[MEDSTUDENT87]

I was wondering what gas to use. My owners manual say 87 if a certain math equation and 93 if another equation. I look on the gas pump next to 93 and it dosn't say the equation that is in my owners manual. So being a BMW I have used 93 and get 29 mpg with highway and light city. My problem is if I floor it it will rev fast up to about 5000 and then when it shifts there is a weird power loss feeling in the car and then once it shifts it gains power back. Also it will not down shift after around 50-55. I recently filled up and used 87 and now the tranny will downshift all the way up to 65 which is nice for passing but I haven't had time to see what my mpgs will be. I am just curious does it not downshift and act weird when it is using 93 cause it creates more power? I dunno it seems that the 87 makes the engine rem more to get to speed creating a more sporty feel. Kinda hard to explain. If u guys don't understand ask the part u don't get and I will try to explain further. Has anyone else had this happen. I will see what it does when I floor it and hold it. Thanx!

[bimmerguy82]

I dunno man that sounds weird. i don't think gas octane will have anything to do with your shifting, but the loss of power can be a few things. Have you checked: your plugs, air filter, fuel filter, injectors?

[Teh Prof]

I would think the downshifting would have a lot more to do with the button underneath your accelerator pedal (the kickdown switch) than it would to do with the gasoline. Perhaps you have one that works only inconsistently?

What year and model of bimmer are you talking about?

[CosmosBlack]

I totally agree with the above comments,
what you explained have nothing to do with the gas octane.

[MEDSTUDENT87]

I have had the plugs changed twice in one year the first time b/c I used Bosch double plats and the engine ran bad on them so I used NGK then it ran better. I replaced the fuel Filter about 15k ago. My air filter was changed a couple weeks ago but was not that dirty just while it was in the shop, why not? I dunno how to check the injecters. I have used two bottles of chevron techron in the gas about 1/2 a year ago. The car I am talking about is a 1990. I hate the stupid chevy tranny it had but I love the car as a whole. The switch has always stoped down shifting after 55mph until this week when I used 87 octane which hopefuly is not destroying my engine. I don't think my motor is knocking at least it dosn't sound like it. thanx

[MEDSTUDENT87]

Well the results are in when I use 87 octane the car runs better all around. I am getting 31.5 mpg with it compared to about 30 or 29 with 93. Thanx every body

[bimmerguy82]

Originally Posted by MEDSTUDENT87

Well the results are in when I use 87 octane the car runs better all around. I am getting 31.5 mpg with it compared to about 30 or 29 with 93. Thanx every body

well that's all good you're getting 31.5 mpg, but that 2 mpg difference can easily be because of driving style. I still does not have anything to do with shifting.

[nukeduster]

the e28 chassis really doesnt like downshifting at highway speeds , my 84 533i did the same thing, wouldnt kick down unless i manually moved the shifter into 3rd.

that loss of power you are experiencing between shifts, is the clutchpacks slipping as they transition from one gear to the next. they are either worn, you are low on fluid, the filter is dirty, or you just arent used to the feeling of an auto tranny.

its up to you which one or combination of those things are wrong.

also, the difference in octane ratings is most likely if they rate the octane in ron, or mon.

in the usa we use pon #'s (average of mon and ron), in the EU they use ron #'s. so for the usa, you use 87 octane. 87 pon is actually 90-ish ron octane.

[MEDSTUDENT87]

Thanx NUKEDUSTER your info was very informative. I was low on fluid I just changed the fluid a few weeks ago and it since has droped and I didn't realize it until you mentioned it. It has improved since I have topped it off. Thank you!