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Old 03-24-2014, 05:26 PM   #1
///Mmm
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* 850i - V12 - 6 Speed *



So I recently moved to Dubai, what a nice city but laws are tooo strict compared to Montreal, anyway my current daily driver is a 90% restored 1993 850i.... and this thing is just different, it's an animal, freshly repainted, it has a brand new OEM CSI body kit, all electrics on the inside work, M mirrors, Alpina wheels, exhaust system wise, OEM resonators and cats are removed, replaced by 4 resonators and 2 mufflers, it sounds like a lambo ..almost.

My brother did all the work, he bought it pretty much from the junkyard, the only good thing was the engine and tranny, it was rusted ,needed everything, he fixed the body, got all the CSI bits, got the interior from another e31. Changed the clutch and fuel pump,the whole cooling system is new,the engine has about 50 000 km and the body about 141 000 km now. Unfortunately I don't have pictures of the build, I have some in bad quality from a camera phone.

The reason I'm posting this is, first I wanna show this somewhat rare car.
Secondly the car misfires like crazy, now it doesn't always do it. If I start the car and it's been sitting for a day, it drives perfect, but after about an hour of driving, it starts to misfire across the whole RPM, part throttle or full throttle same thing, if I turn it on while its hot, same thing, misfire everywhere. But when the car is cold, it usually drives great.
The idle is perfect, check both MAFs, they are good.

I just don't know where to start, it's a V12, parts are not cheap so I don't want to start buying parts left and right and I don't have any experience with V12.If anyone has any idea why it would misfire when the car is hot, please let me know, it would be greatly appreciated

On to the pictures, I apologize for the quality, they are cell phone pics, getting a DSLR soon . Let me know what you guys think .

Bare metal
baremetal 2
baremetal
Almost done
primer
almost done
First wash and cruise
850carwash
850carmeet
850indoor
850gs
Interior
850interior
Back fire
backfire

Last edited by ///Mmm; 03-24-2014 at 05:28 PM.
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Old 03-24-2014, 06:21 PM   #2
DET1990
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misfire could be the ignition coils i had one that would cause a misfire once hot
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Old 03-24-2014, 09:01 PM   #3
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oh man, gorgeous car.
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Old 03-24-2014, 09:37 PM   #4
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On Softlines too. Drooooooooool
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Old 03-24-2014, 10:13 PM   #5
windwagen
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Mis fire?? looks like there is plenty of fire coming out the exhaust!!

Any codes? How do you scan a 1993 anyway?
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Old 03-24-2014, 10:21 PM   #6
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Sick looking car dude!

I don't know know much about the v12, but it sounds definitely related to temp. My guess is it wouldn't be related to the coolant temp sensor, but I'd look at the o2 sensors and see that they are functioning properly. The only other thing I could suggest is something going wonky with the electronic throttle, but it's rather unlikely. Try swapping the computer that controls it to rule it out.
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Old 03-24-2014, 10:53 PM   #7
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Since the problem starts after an hour, I think that would rule out coolant temp. Coils seem more likely - but is it just one???
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Old 03-24-2014, 11:15 PM   #8
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doesn't the v12 have two seperate computers running it?

You could rule out the coolant temp sensor and o2's by unplugging them (afaik)

is the car throwing codes?
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Old 03-25-2014, 12:08 AM   #9
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Quote:
Originally Posted by propr'one View Post
doesn't the v12 have two seperate computers running it?

You could rule out the coolant temp sensor and o2's by unplugging them (afaik)

is the car throwing codes?
The old ones did, for the 750's anyways. Not too sure about the 8's. But the old E32/E38 V12's were notorious for computer problems, also related to ignition coils (it burns the coil!) and some TB problems. Some vaccume and injector problems are possible. The V12 is simply amazing when it runs, but does come with its problems....
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Old 03-25-2014, 12:45 AM   #10
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Well first off I must say your car is absolutely gorgoeus, always loved the 8ers and yours is on top of that list with the alpina and CSI bits....

Secondly, in dubai (closer to Sharjah if im not mistaken..) theres a street called "BMW street"

Ask the locals about its where abouts, its literally bmw shops on the right and left for a about a KM stretch... Im going to ask a friend of mine about the name of the street and hopefully he can give me the actual name of it, but its mostly known as "BMW street" lol

Gluck man
Faisal
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Old 03-25-2014, 03:42 AM   #11
///Mmm
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Thank you guys for the nice comments..

The engine is controlled by 3 ECUs if I understand correctly, one for each bank ( cyl 1-7 and 7-12) and another ECU to sync both.

Now the car doesn't have ignition coils like an M50, this is the M70 and it has a pair of distributor cap and rotor with spark plug wires like an M20. Changing them would cost about a $1000 in parts

The check engine light never came on, the car idles perfect even when its hot and misfiring. ill try unplugging the O2 sensor when it's hot and see if it acts differently.

I understand when the car is cold, the engine runs rich therefor any vacuum leaks or O2 sensor problem could only be affecting the car when it's hot. Is that correct or I'm wrong ?

Could it be that when the car warms, the old spark plug wires expand and lose contact thus giving the misfire ?

Could it be a compression problem?

Thx again for the help, I just want it to run an nice as it looks

Faisal I'm aware of the " BMW street" haha, I just don't like people playing with my car...Most BMW shops haven't touched a V12 ever..

Also more information, don't know if it helps but the more the better... The average fuel consumption is between 16-18L/100 km depending how I drive which I believe is normal for an old 5.0L V12 . I once saw 48.9L/100km in stop and go traffic
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Old 03-25-2014, 07:08 AM   #12
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A misfire after the car has been running for a while can also be a dying fuel pump. Rig up a fuel pressure gauge against your windshield and try to replicate the symptoms. See if there is a pressure drop when it's running poorly.

Beautiful car, and Dubai seems like an awesome place!
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Old 03-25-2014, 10:08 AM   #13
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if the car reall has a dizzy for all 12 cyl's (post pics, that i gotta see), its almost certainly related to that, or the ignition coil (there still has to be one).

I really doubt its a fuel pump. If it were, you could re-prime the fuel pump and start the car, and at least for a few moments the problem should theoretically go away.
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Old 03-25-2014, 10:34 AM   #14
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oh thats hawt!!!
thanks for sharing.

post some vids
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Old 03-25-2014, 10:41 AM   #15
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When the issue happens, can you rev the engine while standing still and hear/feel it miss? If so, get a can of carburator cleaner or starting fluid. Hold the rpm steady, spray the fluid in the intake, if the engine smooths out, it's fuel related. If it doesn't then you know it's probably ignition related.
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