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Matt
Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 20580
Experience:  BEng hons Mech engineering, in auto industry 22 years
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car stops running when on motorway when driving for about 90

Customer Question

car stops running when on motorway when driving for about 90 minutes it starts up again no probs .thenstops every half mile when driving in about town there is no problem
Submitted: 2 years ago.
Category: BMW
Expert:  Matt replied 2 years ago.
Hello

This could be a wiring issue as things tend to expand when hot ( hence it only occurs on the motorway whrere the load is high enough) and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor


Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Also replace the spark plugs if any of them fail this checklist:

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp


Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V


Also check for exhaust leaks before the o2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

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