How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Engineer
Category: BMW
Satisfied Customers: 20395
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Type Your BMW Question Here...
Matt is online now
A new question is answered every 9 seconds

My BMW M3 won't start after driving for a while. It starts

Customer Question

My BMW M3 won't start after driving for a while. It starts right up at the beginning of the day but if I cut it off, it will not start up immediately but takes 5-20 minutes before starting again. Help.
Submitted: 2 months ago.
Category: BMW
Expert:  Matt replied 2 months ago.

This could be a wiring issue as things tend to expand when hot 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

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

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.

and it could be a the crank position sensor is steadily failing as these have a good habit of working when cold and then failing as everything warms up and expands

Expert:  Matt replied 1 month ago.


do you still need help?

Bear in mind that the site takes a deposit from you at the beginning andthis is held by the site until you rate my answer at which point the cash issplit between the site and the expert. I am only paid for my work on thisquestion if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Related BMW Questions