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Discussion Starter #1
Hi all,

Just wanted to see if anyone has had the same problem I'm getting.
Here are my syptoms:

While I am driving the car turns itself off and restarts again, it only restarts as I am rolling in gear.
The engine makes no strange noises when this happens, and it will do this about numerous times and then just stop doing it. It happens randomly, the car will be fine for a couple of weeks and then start doing these symptoms again. I would really like to find out why this happens.
I did have a amplifier attached, and its been months since I disconnected it. Today was the worst as it happened 3 times and then the traction control light stayed on, I pulled over, turned the car off for a minute, restarted the car and it was fine the whole way home.
I was thinking if it was a petrol pump issue or even ignition coils, but the engine is not missing a beat. It's starting to drive me mental :grrrrr:, my wife drives the car sometimes and I don't want it to fail on her, if it does I'm not going to hear the end of it and she will persist on me changing the car, but I did advise her when I brought the car she would be the first to go lol. I've always worked on cars myself as I don't trust any local mechanics, if never had any issues with it.

Any help would be appreciated
It is an e39 m5 2002 model
 

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Hi, first port of call would be having someone trustworthy run diagnostics on the car and try and pull up some error codes. Don't be tempted to go down the route of changing out various components to try and eliminate possible problems. Good luck.
 

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Discussion Starter #5
Sweet, I have checked the battery and connections and they are fine. I will research to find a trust worthy diagnostics mechanic to see if there are any dtc's on the memory. But do you guys think that the battery could be at fault?
 

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Back when I had an e34, the root of all problems was the fusible link. If the e39 has one, I would look there.

Other than what the codes will tell you, can you rule out fuel pump / filter
 

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When you say 'turns itself off' you mean all the electrics cut out or the engine stops? I assume electrical as engine stop in gear while moving would really be felt.
 

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Discussion Starter #8
Yes, all the electrics turn off, the ignition lights come back on and car starts back up as its rolling in gear
 

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Sweet, I have checked the battery and connections and they are fine. I will research to find a trust worthy diagnostics mechanic to see if there are any dtc's on the memory. But do you guys think that the battery could be at fault?
A lot of people's cars on here (mine included) have had the exact same symptoms, and the majority of the time it's a bad battery or bad battery connections.

Is it an aftermarket battery? How did you test it?

Yes, all the electrics turn off, the ignition lights come back on and car starts back up as its rolling in gear

So you can rule out petrol pump and ignition coils.
 

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Discussion Starter #10
I have cleaned the battery connections with some wire wool, and then carried out a continuity test with my tester between the battery terminals and the main wires. The battery itself is bmw battery. I have checked the full history on it and all the invoices and nothing states that the battery has ever been changed. When I read about others having similar problems a lot of statements were made that the car has trouble starting after sitting idle for a couple of days, I have the the car sitting for over a week sometimes and it always starts first time. I will try the diagnostics first and I will also try a new battery, It won't hurt getting a new one or is there anyway I can test the battery?? Thank you for your advise guys, really appreciate it.
 

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How many miles do you have on the car? - there is a common issue with the ignition switch on E39's - almost a wear item however the symptoms usually affect secondary electrical systems only in odd way, not the whole car. As others have said, battery wiring or positive link isolator issue (can't remember correct name).

Have you checked the common ground points as well in engine bay - worth checking.
 

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Discussion Starter #12
Car has done 123k, I also thought ignition switch but I've messed around with it while the cars started to see if it does make the car turn off, but it didn't. There are a few things I've tried as the first time it happened was about 8 months ago. But because its been intermittent I never posted it. But today it bloody pissed me off so much. I'll have a look at these fuse links, just got to have a read up about them to see what they actually do lol
 

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change your ignition switch have seen them go bad and do very strange ****
 
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It won't hurt getting a new one or is there anyway I can test the battery?? Thank you for your advise guys, really appreciate it.
In the states we can test our batteries at any local auto parts store. I'm not sure about over there.
 

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Doesn't sound like a battery problem, more like an intermittent bad connection.

There is a connection at the other end of the -ve battery cable that has a reputation for coming loose. It's in the RHS of the boot behind the liner. There are some other heavy cable connections behind there you can wiggle check as well.
 

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If I was you i'd take a look in the ebox where the ecu lives and check all the connections - make sure no water is getting in there etc. Sounds like you losing power to DME amongst other stuff - my thinking is if engine is stopping then DME must be losing power as well - worth a look.

When you read codes I imagine you'll have a huge selection to run through - losing power while running must confuse then hell out of the cars computers!
 

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In the states we can test our batteries at any local auto parts store. I'm not sure about over there.
On a previous car, I had someone 'test' my battery on symptoms, tester showed it to be fine, symptoms continued, swapped the battery in the end and symptoms disappeared. Not a big fan these battery tester things now.

I also, on a previous car, had a coil pack go bad (when finally swapped out, it was very hot, and smelled of burning plastic/rubber so assuming internal arcing etc.), and it caused the car to just cut while running. No noises, no drama, just stopped and coasted to a halt. Ignition lights as you say, as if it had stalled. But these are very different engines, and may bear no similarity. Just sayin'.
 

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If I was you i'd take a look in the ebox where the ecu lives and check all the connections - make sure no water is getting in there etc. Sounds like you losing power to DME amongst other stuff - my thinking is if engine is stopping then DME must be losing power as well - worth a look.
Power is supplied to the DME from a fusebox under the (USA) passenger seat. That fusebox is directly connected to the battery. Check the area 68FB mentioned, if it's fine I would check the under-the-carpet fusebox next.

On a previous car, I had someone 'test' my battery on symptoms, tester showed it to be fine, symptoms continued, swapped the battery in the end and symptoms disappeared. Not a big fan these battery tester things now.
Did it test the cranking amps or just the voltage?
 

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I've had this problem before and was caused by bad MAFs. Never threw a code but changing the MAFs fixed it. Car would just cut off when gliding but start up again no problem by engaging a gear or turning key.
 

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Discussion Starter #20
Thank you for your help guys, car hasn't done it again since Monday, I know it's gonna do it again
So wen I get some time on the weekend I will work through every thing and let u know what the outcome is, only thing is I won't know if anything has an effect as its so intermittent. I'll keep you updated
 
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