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Discussion Starter · #1 ·
Hi all!

I've had my M5 for 11 months now and have clocked up just under 40,000km in that time. No issues at all through this time, until ...

Yesterday, the check engine light came on. Talked to the BMW dealer, who (predictably) said I'd better bring her in. 10 minutes later, light goes off again and shows no more. Engine running fine...

Today, driving home for work all of a sudden it's like driving a one-bladed chaff-cutter!! Lots of vibration from under the bonnet, keep it below 3000 rpm and it was undriveable. No power at all, and NO warning lights at all!!

Then after about 15 minutes of this, it clears itself again and is as right as rain!

What's going on? I was wondering whether it may have been a blocked injector but since the engine light appeared the day before could they be linked? Any other thoughts?

Maybe its time to visit my friendly dealer!

Cheers
Andrew E
 

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I had something similar happen with my M3 about 3 years ago (which meant the car was about 1 year (around 15k miles) old) I was at a stop light. the light changed, I engaged the engine and the car started vibrating and felt like something was draining engine power from it. I pulled over- turned the car off for a few minutes- and turned it on- the car was fine. until a few months later the same thing happened in heavy traffic. I didnt have the opportunity to turn it off (traffic was going around 15mph) but I reved the engine a little and it came around. I called the dealer immediately and they said if it happens again to bring it in. It never happened again! My guess is the computer was at fault and when it was serviced by the dealer (Im good about that) they made a change to the computer software as a routine and this fixed it. Just my guess.

ME
 

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I had a similiar experience with about 5000 miles (8000km) on my car. I was showing off my car to my brother and gave him a demo ride. When I slowed down and pulled into his street I noticed it felt like it was missing and low on power. I pulled into his driveway and it sounded like a loud diesel. I did not know what to make of it. I am thinking, ****. I cannot figure out where this ticking/knocking sound is coming from. Anyway, I shut it off, wait a few minutes and it now it is GONE. It has not happened since. I did not even bother to call the dealer. The thing that got me was, that I had driven the holy **** out of the car the week before at the race track and no problems there. I mean every shift to redline, tires squealing, etc. So, I will wait and see. I am at 6000 miles now and have not had a repeat.
 

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I had similar occurances while tuning blown
M52s and with stock m52s. Two different possibilities come to mind. Both cause an unquestionable misfire; the kind that makes you not want to drive the car.

My question to you andrew is;

When you say that you lost power, did you still have 7/8 or 3/4 power or was it more like less than 1/2 power? Above 3000 RPM,
did it have decent part throttle power making it easy to drive the car at 70-80 mph
or did you want to crawl home at 30 mph?

Possibility #1

Misfire detection; The ECU has detected via, the crankshaft sensor, an abnormal crankshaft event which has the caracteristics of a misfire on a paticular cylinder. This can occur due to a "real" misfire (fuel ratio problem, spark problem or
the painful one; compression problem) or any other thing that might cause the crankshaft to have something other than smooth, incrementally changing, mathmatically predictable behavior that has been seen before and dubbed "normal" while operating in the emissions zone, < ~ 4500 rpm. If the ECU sees an "abnormal" acceleration it associates that with the cylinder that just fired and condems it as not worthy (Does not play well with others) and gives that cylinder a "time out" turning off its injector thereby saving the catalytic converter from damaging unburned mixture. After a brief time and when the crankshaft has been operating in a steady state condition for a brief period the ECU will let the offending cylinder out of the penalty box for a test if it passes the test he will be allowed to stay in the game and if not he will be placed in the penalty box again and the cycle continues until a BMW magician cures it.

One occurance of this event will most likely not turn on the check engine-service engine soon light but two or more will (>96). The driver may not always percieve the occurance of such an event. Light or not all such occurances will be recorded by a fault code.

The Cure;

> Shut engine off and restart after 30 secs.
(as little as 5 secs will work)

or

> Drive steady state at 3000 rpm in 3rd or
4th, don't move the trottle for about 10
secs and you will feel it turn back on.

If that cures it and it does not come back and the car is good as ever, reflect on your driving behavior imediately prior to the occurance of the event. Banging gears, clutch drops, ridiculous downshifts, cathching air, rear wheel lock up all the things I consider "normal" can be viewed as "abnormal" when seen through the eyes of a crankshaft sensor looking at a wildly occilating crankshaft and assuming that its not your fault.

You used to have to drive smooth to keep the cars on the pavement, now you have to drive smooth to keep the motor hitting on all holes. Especially on those demo rides!!

Possibility #2

Crankshaft sensor intermitent failure.

Used to be if your crank sensor failed you were dead in the water and if it glitched you got a miss or two on a pull or just strange behavior.

Now if the crank sensor fails or glitches it gets a "time out" and the ECU then attempts to run your engine off the cam postion sensor alone. This is a fail safe feature which might just barely get you home in an emergency of such magnitude that your car didn't matter anymore. I just can't bring myself to drive them in this mode, Big miss, multi cylinder miss and way down on power.

The cure;

Shut engine off, wait 30, restart, pray
or
Shut engine off, pray, wait 30 while praying, restart

If it runs good be thankful and drive home or to your shop to see if you have a crank sensor fault code. If you do and it has occurred mutiple times (according to the modic not the driver) change the crank sensor. Resume daily prayer.

Do not assume driving behavior caused this fault. It will happen again.

Crank sensors on M52s have been a small problem. Early cars can be updated and will be updated under warranty for bonified failures. Sensor and new wiring adapter required ~ $200 I think.

On the E39 M5 I do not know of any problems or updates. The failure of the crank sensors
is and always has been a very inconsistent thing as there are sensors out there with a couple hundred thou working fine and other bad ones at as little as 30 grand. Typical failures of a typical population.

Hope this helps,

Hammer on!
 

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Discussion Starter · #5 ·
Thanks for your responses. To answer the latest question, probably felt like around 1/2 power. I had been driving home in flowing traffic for about 15 minutes at a steady 115km/h (say 65-70mph) before this happened, so no abnormal situations for the crank sensor to get screwed up.

It would hold 100kp/h after the occurence, but I didn't want to push it much past that the way it felt. I'll certainly take it to the dealer for an examination of the diagnostic codes to see what it can find, and also take along these responses!! I'll update the board once I have gotten a response on it...

Thanks for your messages.

Cheers
Andrew E
 

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Discussion Starter · #6 ·
All

More info after discussions with my M technician. He is saying that the likely culprit of both occurrences is a bad batch of fuel - the engine warning light will come on if a higher level of contaminants than is acceptable is detected in the fuel.

The system is supposedly designed to drop a cylinder or two if contaminants get too strong until it is burned through.

They can check the diagnostic logs at my next visit to determine exacly what it is that occurred.

Cheers
Andrew E
 

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Andrew e

I realize that you a just repeating what the tech told you based on a discussion with you.
Please don't take these comments personally.

The BMW tech said:

"the likely culprit of both occurrences is a bad batch of fuel - the engine warning light will come on if a higher level of contaminants than is acceptable is detected in the fuel."

Oh, the old bad gas.
Can I assume that you are buing high quality 92 or better from a reputable distributor ?
If you are not do I really need to say something. What kind of contaminents ?
Does the motronic system have a fuel contamination sensor ? How does it decide which cylinders are the ones to shut off ?
How does shutting of a couple of holes going to help the situation if it was bad fuel ?
Are you sure that you weren't talking to a service manager as oppossed to a real tech ?
Service managers know more about these cars than anyone; and without one day of class!
amazing!!

Further the alledged tech states;

"The system is supposedly designed to drop a cylinder or two if contaminants get too strong until it is burned through."

I see, only a portion of your tank of fuel was bad (just one little slug floating around in the tank) and once that gets burned thru everything retuns to normal.
Got it. I was worried that you had gotten a whole tank of bad gas at rotten robbie.

As you say:

"They can check the diagnostic logs at my next visit to determine exacly what it is that occurred."

They can determine what MIGHT have occurred
you hope. Depending on their skill they might make the right move. Thank god for warranties. Best of luck!!

As long as the light goes back out after an event like you had, don't sweat it too much.
Serious problems will cause the light to stay on. However, if the motor doesn't feel right do not conclude that there is nothing wrong just because the light is out.

I wish I was worried about my new M5 tonight.
 

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Just had a "missfire" incident on cylinder 5 & 6 today at 3250rpm. SERVICE ENGINE SOON flashes. Everything was back to normal after lunch. Thanks for the explanation, RFS.
BTW, I'll remember the daily prayer ritual!
 
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