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Discussion Starter #1
Have searched a lot on here but cant seem to find anyone with the same trouble as I am now experiencing.

I have a 1991 420 sel which when running is still smooth and powerful as it is meant to be however on random occasions it decides to cut out without any type of warning - just as though you turn the key off. This can happen at any time - just after starting or when at normal running temperture. Strange thing is when you go to restart the car all instrument warning lights come on except for the check engine light and the fuel pump does not start up. I know its going to start when the light does come on normally and goes out when started.

After the first time it happened it was put down to the aftermarket alarm it had as this had an immobiliser. Had it disconnected and ran fine for about a week then one day at the lights it died blocking traffic :(

So after getting it towed home I removed the FPR and tried jumping this but nothing - engine light still out.

Have discovered though if I disconnect the battery for a few minutes then put back on it will start fine again and the light comes back on. Sometimes it won't work and you have to leave for bit longer or disconnect the electric fans for the radiator. It is worth noting that sometimes the fans will come on and stay on even with AC off and car cold and sometimes they give short bursts. I have tried leaving them disconnected thinking it was somehow causing a fault but car still randomly stalls.

Any thoughts?
 

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Discussion Starter #2
Further to above, took for another drive with new fuel relay in hand. After bout half hour driving it decided to cut out - was dark this time and noticed that the ABS light and check engine light turned on and off a few times before it cut out. Changed the relay and still nothing. Disconnected the battery left a few minutes then reconnected still nothing. Was just up the road so was able to coast home and leave on the drive. Any help would be appreciated!!
 

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Is your ignition switch faulty perhaps? Sounds like symptoms i had with another car, took me ages to figur out because it was so random. The weight of keys dangling had caused the ignition switch to wear out and it randomly cut the engine as if it had been turned off.
 

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A six inch wire with a fuse hooked into a B+ side then to the KOER side of the fuse panel will rule out the ignition switch. The reason for a fuse is your back feeding the circuit (+) bypassing the switch, and if there is a short it will pop the fuse before ruining anything. Which you may be doing by just jumping random stuff.


The fuel pump will not turn on if the ECM light doesn't light up with the key in KOEO.


B+ side: cigar lighter, headlights anything that will come on without the key.

KOER side: anything that comes on only with the key.


By no means is this what is wrong with your car, just a suggestion to diagnosis.
 
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