# Starts, runs 5 sec, dies



## GJ (Nov 25, 2006)

I have a 91 750il. 75K miles on it. The car starts up but dies after about 5-10 seconds. It had the 60,000 mile service with platinum plugs. Possibly O2 sensors? Fuel pump?


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## 98740il (Feb 7, 2007)

GJ said:


> I have a 91 750il. 75K miles on it. The car starts up but dies after about 5-10 seconds. It had the 60,000 mile service with platinum plugs. Possibly O2 sensors? Fuel pump?


 run a code scanner.couldn't be fuel pump or 02 sensor


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## TerryY (Jul 20, 2003)

The M70 V12 doesn't seem to like platinum plugs. For that matter neither does the V8.

Fuel pump runs to prime the system when you turn the key to run. 

Then the engine computers take over when it starts--a sensor failure will turn the fuel pump(s) off for the side of the engine that saw the failure.

It sounds like you have instant failures on both sides.

Pull the #6 spark plug--drivers side with the sensor donut around the wire. If it is fouled either clean it up or replace it and see if the engine runs on 6 cylinders but stays running. Make sure that the wire is not broken and is pushed all the way down on the spark plug as well.

That donut on the wire is the ignition sensor for the computer and if the plug it is attatched to misfires or doesn't fire at all the engine will "save" itself by killing the fuel to that side of the engine.


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## GJ (Nov 25, 2006)

I really appreciate the input. As you know the plugs on the V12 are impossible to reach. That's why the platinum ones were put in - to postpone changing them as long as possible. Up until now it's been running perfectly. What are negative effects of the platinum plugs? I'm mechanically minded, but not qualified to touch this car so it's with my mechanic and his first thought was the fuel pump. And of course, he initally asked if there was fuel in the tank :eeps:


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## GJ (Nov 25, 2006)

The computer says there's something wrong with the drive shaft sensors. We'll see if replacing them fixes the problem. Apparenly the computer shuts things down to save the catalytic converter.


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## TerryY (Jul 20, 2003)

Drive shaft sensors? 

Crankshaft sensors or camshaft sensors each affect one side of the motor. 

Crankshaft sensors are somewhat gap sensitive (1 mm)

Platinum plugs just seem to not perform well in BMW V12 and V8s--Bosch Standard electrode plugs seem to be the best overall.


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## GJ (Nov 25, 2006)

I thought he said drive shaft. But, with the German accent I could certainly be mistaken. And having given up coffee recently I'm not as alert as I used to be.


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## GJ (Nov 25, 2006)

*update*

It was two crank position sensors. About $120 each plus a substantial amount of labor.


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