Start Stop Problems

[Audun]

Hey guys. I got a BMW 1-Series 2004.

It got all kinds of variations of start stop problems. (3 shops thought it was the red long battery cable that runs under the car, it was loose in the back) But it wasn't it as they fastened it. It sometimes starts with no problem, then it stops suddenly while driving, it sometimes don't start at all with no ignition sound, and sometimes it tries to 'give' with ignition sound but never 'grabs'.

Starts fine without problems
Doesn't start, without ignition sound
Doesn't start, with ignition sound

What could this be?!

Thank you for any insight.

[JimD]

I don't know but maybe a description of the system will help. The current required by the starter is so high that they use a relay, usually on the starter, to connect the starter to the battery. So you need a good connection between the battery and the relay and between the relay and the starter and between the relay and the push button circuit on the dash. Any looseness or otherwise bad connection in any of these will turn into intermittant starting.

But you also said it dies while driving. That would seem to be something different, unless the connection to the battery is bad and that is causing both the starting and the running issue - but that was supposed to have been checked if I understand your comments. Cars need two things to run, spark and fuel/air. If a cylinder starts to miss, the car often will not idle but will run at higher rpm. Missing could be a plug, or an injector or other things.

[chalupa2000]

What type of transmission do you have... The reason I ask is that both the brake pedal and clutch pedal have switches that allow the car to start when pressed and the wiring or the switches may be glitchy