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Discussion Starter · #1 ·
When I accelerate at about 2500rpm I hear a "clattering" or "rattling" sound. I assume it is detonation. I was advised to try a higher octane fuel, which I did. I also used a fuel additive (octane booster) which has not had any noticeable effect. I have read that a "colder" plug may fix the problem. So what exactly is a colder plug and could it have any adverse effects on my car? If this is the route I should take then what plug should I try. Are there any other possible causes and cures for this problem if the plugs don't work?
 

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Humble E34 lover
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Welcome to the Fest !!

Your car has knock sensors that automatically retard the timing whenever pre-detonation is sensed (long before you can hear it). I doubt it is pre-detonation knocking you are hearing.

I would suspect a worn vanos unit (well, worn seals anyway). One way to try to narrow it down to this is to follow these steps.

- Crank your car. Listen to it at idle. It will likely sound okay.

- Press down on the throttle linkage and rev the engine up (not to high of course). Do not do this in rapid form. Take 2-3 seconds to rev the engine.

- Put your ear as close to the vanos unit (at the front of the head/valve cover) as is safely possible (no necklaces, long hair etc.).

- If you hear a rattle, try to hold the throttle linkage at that point to try to verify it if is the vanos unit.

The vanos unit can be rebuilt. One person here just rebuilt theirs and another is just getting ready to do it.

Hope this helps,
Steve

PS: Not to insult your intellegence, but make sure that you have enough oil in the engine. Ask me how I know :rolleyes:
 

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A colder plug is a normal single pronged ngk plug or the like. Hotter plugs are those four prong things that can cook your plug sockets. You need a consistent electrical spark, not a nuclear explosion.

On a previous car I used the four prong things for awhile. I had similar issues to you except worse. Coking all over the socket and plugs themselves. It was literally cooking my engine. Others here say that they are great, but they haven't replaced them yet.

Ngk single pronged or denso iridium single prong works well.

The goal is to ignite the gas without increasing pointless waste heat.
 

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Actually, a the heat of a plug has nothing to do with the amount of ground electrodes. It's the length of the ceramic insulator around the positive electrode, that's the one down the center. The longer the ceramic, the hotter the plug. A shorter insulator allows heat to be transfered quicker to the body and the head allowing the plug to cool sooner. If the plug is too hot of a heat range, it can remain hot enough to cause pre-ignition. Some guys use a hotter plug if the engine is worn and burns oil in an attempt to get a longer plug life. If you use too cold of a plug in an engine that doesn't require it, carbon will build up quicker. I doubt spark plugs are your issue unless yours are severely fouled and the carbon deposits remain hot enough to pre-ignite the fuel before the plug fires.
 

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Discussion Starter · #5 ·
Thanks

This is the first BMW I have ever owned (bought it for my son's first car). It was a one owner with 135k mi on it and seems in good condition. I am researching the vanos thing because i have never heard of this. I will try your suggestions. I have found a site ... drvanos.com and I'm reading up on it now.

One more question on the subject ... Is this now or will this become a driveability issue?

Also, I have the original operators manual and can't find much info on this either:
What does the "maintenance" indicator light that illuminate when you have your key turned to the on position tell you? It is a series of green, yellow and red. I have one yellow left so I changed the oil and filters. The lights did not change so I assume that it is not and oil life indicator or it must be reset some how. Anyone?

Thanks again in advance. I am trying to do some of these projects with my 15 year old son, you know get him off the couch and away from the video games, so I appreciate all the input and find you guys very helpful.
 

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Humble E34 lover
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See my responses in red below

This is the first BMW I have ever owned (bought it for my son's first car). It was a one owner with 135k mi on it and seems in good condition. That's very good low mileage for this car. I am researching the vanos thing because i have never heard of this. I will try your suggestions. I have found a site ... drvanos.com and I'm reading up on it now. Doing research is good. Make sure to do a lot of research and ask questions here before you pull the trigger on proceeding with any work on the vanos unit.

One more question on the subject ... Is this now or will this become a driveability issue? A vanos with worn seals can become a driveability issue from the perspectiive of power delivery. You can develop flat spots in acceleration etc. When the vanos is operating normally, the power delivery is very linear and the car pulls strong throughout the entire RPM range.

Also, I have the original operators manual and can't find much info on this either:
What does the "maintenance" indicator light that illuminate when you have your key turned to the on position tell you? It is a series of green, yellow and red. I have one yellow left so I changed the oil and filters. The lights did not change so I assume that it is not and oil life indicator or it must be reset some how. Anyone? The indicator lights just give you an idea when the car needs to be serviced, but it is not based solely on mileage, but is supposed to take driving styles into account as well. These lights are easily reset with a bent paperclip. A quick search on Google for "E34 service light reset" should locate the site easlily enough

Thanks again in advance. I am trying to do some of these projects with my 15 year old son, you know get him off the couch and away from the video games, so I appreciate all the input and find you guys very helpful. Props to you pops :thumbup: for taking a proactive approach and being involved with your son. He will gain valuable character and wisdom from these types of activities.

Steve
 
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