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Discussion Starter · #1 · (Edited)
The car always felt very jerky to drive at low speeds and there was a flat spot right at the start of the throttle opening.

Then the car would hesitate at 2000rpm and 3000 rpm.

I did an oil change last week and decided to see if I could reach down to the crank sensor. This was easy. I got a small brush and started cleaning away.

Surprise surprise! Very thick gunky sh8t on crank sensor and all around it.

I spent a good 15 mins continually sparying engine cleaner + brushing away until I could put my hand down there and it not come back black.

Results:

Flat Spot gone, no more hesitations. Much more smoother running. Much easier to drive at lower speeds.

COST? 15 mins + engine cleaner.

TIPS:

Dont do it when the engine is hot, removing the fan will make things much easier. Make sure you wear gloves as engine cleaner is not kind to your skin and youll stop them going black.
It is going to be very very dirty down there I promise you!
 

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Cyrus said:
The car always felt very jerky to drive at low speeds and there was a flat spot right at the start of the throttle opening.

Then the car would hesitate at 2000rpm and 3000 rpm.

I did an oil change last week and decided to see if I could reach down to the crank sensor. This was easy. I got a small brush and started cleaning away.

Surprise surprise! Very thick gunky sh8t on crank sensor and all around it.

I spent a good 15 mins continually sparying engine cleaner + brushing away until I could put my hand down there and it not come back black.

Results:

Flat Spot gone, no more hesitations. Much more smoother running. Much easier to drive at lower speeds.

COST? 15 mins + engine cleaner.

TIPS:

Dont do it when the engine is hot, removing the fan will make things much easier. Make sure you wear gloves as engine cleaner is not kind to your skin and youll stop them going black.
It is going to be very very dirty down there I promise you!
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where is the crank sensor exactly?
 

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Discussion Starter · #3 ·
Its just behind the viscous fan coupling. If you feel the crank pulley youll find it towards the top, its a round cylindrical shape.
 

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Cyrus said:
Its just behind the viscous fan coupling. If you feel the crank pulley youll find it towards the top, its a round cylindrical shape.
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So you have to dip your arm right down in there, can you actually see it from the top of the engine?
 

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Discussion Starter · #5 ·
Yep, arm down.

using a torch you will bale to see it.

Best thing would be to remove the fan which will make things 100 times easier. You can see it properly and make sure youve cleaned it aswell.
 

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Cyrus said:
Yep, arm down.

using a torch you will bale to see it.

Best thing would be to remove the fan which will make things 100 times easier. You can see it properly and make sure youve cleaned it aswell.
Thanks sir. I will give it a go this weekend, a mission!
 

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Cyrus said:
I spent a good 15 mins continually sparying engine cleaner + brushing away until I could put my hand down there and it not come back black.
Thank you Cyrus, good to know! So removing dirt on the outside of this sensor is enough to cure such problems; it doesn't have to be taken out, right? The problem is dirt causing bad contact then?
 

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Discussion Starter · #8 ·
There isnt really an need to take it out because alot of it is visible from where its mounted anyway.

Dirt/sludge/crap getting int theay is defintaley going to cause a bad signal being produced.

As I said, my problem is cured and. I had already tried a different MAf unit to make sure it wasnt that that was causing the problem. I even treid another ECU which made no difference so the last thing left was all of the sensors. I changed the Throttle position sensor....made no difference. Therefore the only other logical sensor to check was the crank sensor. They dont normally fail and readin an old thread on here sugested I should clean it.

Trust me on one thing though.......the mount of crap I found on both the M5's Ive had is a serious amount!
 

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I have carried out the same "mission" several times. It is well worth the effort.
The main reason for the oil to clogg up there is that there is an oil leak somewhere at the front of the engine. I changed all the gaskets on the front shield and to the oil pan at no effect. I found out, on this board, that the reason for all the oil probably is that there is a bolt for the water pump that is threaded into the engine block AFTER it has passed through the timing chain casing. This will be the bigger of the two bolts that hold the 6 mm thick engine lift.There is no seal there so I put an O-ring on both bolts (Bolt through engine lift - washer - O-ring) and re-installed. I washed the whole area last night and now I will see if this helps.
So, if you don't hear from me on this sunbject within the next few weeks, it worked :)
 

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Hmm, sounds like that's a job for the weekend for me too - mine tends to be snatchy on light throttle and I was thinking of running through all the sensors and connections to check them.
 

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I changed mine, and changed the 6th cilinder cable, that has a sensor on it.
My problem was a bit bigger, as my car did not start at all.
 
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