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E34 (1989 - 1995)

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  #51  
Old 04-06-2013, 10:12 PM
boriska137 boriska137 is offline
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Smile 1990 535i

Quote:
Originally Posted by injunmort View Post
are you using premium gasoline? have you changed the fuel filter recently. i would fill with premium and seafoam, drive it for awhile and see if there is any improvement. my wifes car does the same thing when she cheaps out on gas.
Hi I have a question. My 1990 535i owners manual said our vehicle require 87 octane not 91. would 91 octane make a better choice ?
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  #52  
Old 04-06-2013, 10:37 PM
boriska137 boriska137 is offline
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boriska137

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Originally Posted by injunmort View Post
my bad and appologies, my wifes 1990 535 m30 says on the fuel door "premium unleaded only" my 1990 525 m20 says, in the same location "unleaded fuel only" by personal experience and that of other local e34 drivers, if you dont put premium in the 535 it will run poorly. this happens whenever my wife puts regular in her 535. my w124 mb has the same requirements as well "premium unleaded only" when you put regular in it, it runs like ****. no power, hesitation and rough running.
Sorry, but I have a 1990 535i and on my cars fuel door says "unleaded only" So how come the same year vehicle can have two different requirements ? Any idea? thanks
Boris.
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  #53  
Old 04-06-2013, 11:52 PM
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_Ethrty-Andy_ _Ethrty-Andy_ is offline
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Your M30 engine isn't technologically advanced enough to make the most of 91 octane in the USA (95/98 RON elsewhere in the world). 87 will be fine for your car.
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  #54  
Old 04-07-2013, 12:56 AM
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DanM5 DanM5 is offline
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Doesn't 98 octane just burn better then 9?? the octane rating is just the petrol's point of ignition, or ability to ignite, yeah??
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  #55  
Old 04-07-2013, 02:56 AM
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_Ethrty-Andy_ _Ethrty-Andy_ is offline
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Quote:
Originally Posted by DanM5 View Post
Doesn't 98 octane just burn better then 9?? the octane rating is just the petrol's point of ignition, or ability to ignite, yeah??
yes

meaning later cars can increase the timing and extract more of that power.

but the M30 cant do that. Yes, it will run smoother. but no better economy/power. just placebo
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  #56  
Old 04-07-2013, 03:11 AM
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DanM5 DanM5 is offline
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So I've been waisting my $1.62 per litre for nothing haha!! Not to mention the fact that my car is an alcoholic!!!
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  #57  
Old 04-07-2013, 08:15 AM
snowsled7 snowsled7 is offline
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Another two year old thread resurected

Probably best to start a new one.... especially since the thread you brought back up is full of bobby bag o donuts mis-information

Octane is a measure of a fuels resistance to ignite. The higher the octane, the harder it is to get it to flash. Ignition timing and compression are the two major factors in setting an engines octane requirement.

The M30 is low compression. Adding a chip tune advances the timing curve which requires premium, and does manage to take advantage of the higher octane. Stock though, as Andy mentions, there is no power or economy benefit to running premium, NONE.
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  #58  
Old 04-07-2013, 02:14 PM
boriska137 boriska137 is offline
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Thank you much. That is helpful.
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  #59  
Old 04-20-2013, 06:41 PM
MRF4665 MRF4665 is offline
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Well, it's been ~2 years and I'm still having the same issue described in my opening post and it's still making me a little crazy. I'm about to go fork it out at a local repair shop unless I can successfully get to the bottom of the issue without getting fleeced by a repair shop.

To recap - My beloved '90 535i is experiencing intermittent stuttering at low rpm (under ~1500 rpm) when accelerating. When back off throttle or get above about 1500 rpm, the stuttering largely vanishes but has occurred a few times above ~4500 rpm under heavy acceleration. When cruising at highway speed there is no problem at all. The low rpm stuttering problem is more prevalent sometimes and rare at other times and is independent of engine temperature. Idle is rough at times as well.

I've replaced the following items with OEM parts from Pelican:
1) Spark plugs
2) Plug wires
3) Cap and rotor
4) Fuel filter
5) Fuel pump
6) Air filter

None of the above part swaps have had any effect whatsoever in correcting the stuttering issue. I've also cleaned and inspected ICV and throttle position sensor and gained no improvement.

My current best guess is that I have some sort of fuel delivery issue, either with a bum injector or poor pressure at the injector. Could I have a faulty fuel pressure regulator? Any other items that I should consider? Lastly, any recommendations for a reputable shop in the LAX area of Los Angeles that is knowledgeable and won't take me to the cleaners?

Appreciate any assistance.

Regards,
Mark

Last edited by MRF4665; 04-20-2013 at 06:42 PM.
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  #60  
Old 04-20-2013, 07:15 PM
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Piston_broke Piston_broke is offline
What was that noise??
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Interesting thread, all be it an old one. Have read most of it and am very disappointed to see that 2 years on it is unresolved!!
I Googled with the same stuttering problem at between 1,100 and 1,400 rpm and up comes this thread (the most informative of this issue). Roberto has contributed with sound reasoning.

Mine (M535i Euro) is especially noticeable when going around a corner or roundabout in either 2nd or 3rd gear, we have hundreds of r/bouts in my neck of the woods and to that I am forever stumbling my way around and through them. Thing carries on like a pig. I leave the r'bout and it's if nothing is wrong with the old girl. btw, she jumps off the mark like a champion each and every time.

I have replaced the plugs, cleaned the ICV, throttle body, air filter and put in fuel injection cleaner product all to no avail of getting rid of this very annoying and yet persistent problem. Nil issues at high revs.

I do however, fill up alternately with high and low octane fuel each other week, mainly because of fuel prices over here in Australia. Might try running high for a month and see if that makes any difference.

I have not cleaned nor replaced the fuel filter or pump as yet. Guess I'll try those options and see where that takes me.

I have not replaced: cap, rotor or wires.

I'll also try the diesel fuel combo clean and if after the above doesn't work then I'm stumped.
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Last edited by Piston_broke; 04-20-2013 at 07:17 PM.
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