Starting Problems

[Batchelors]

Hi, hopefully somebody can help me.
I go to start my car and the key turns and there is like a piston sound and won't start, I take they key out and it either does it again or starts. Usually takes 2-3 times to start, then drives fine until the next time I go to start it up. Occasionally it starts first time but it's just a lottery.
I've read in other threads it could be the fuel pump relay.
Has anyone had any experience of this?
If so where could I find the relay to replace in hope that this is my problem.
Thank you.

[X5Sport]

Describe the 'piston sound'?  Do you mean it cranks and doesn't fire or what?

Fuel pump relay is about £10 and is on top of the front fuse box - above the glove box.

[Batchelors]

Sometimes it will do a little crank and then other times it won't crank at all and will go straight to a 'psssst' sound and then all the airflow stops. I take key out, put it back in and then it will fire up. The sound sounds like it's coming from the passenger side of the car engine, there also is a strong petrol smell after it eventually starts.

[X5Sport]

If it's been cranking with no start then you will get a strong petrol smell as it will have unburned fuel in the system.

The starter is on the right side of the engine (looking into the bay from the front), at the back under the inlet manifold assembly.  Not sure what you are hearing as there is no air starter on an X5!

When it does crank, is it fast or slow (almost as if the battery is dying)?  If slow, are your battery volts OK - 12.4 or better?  Lower than 12V indicates a bad battery.  With the engine (eventually) running you should have around 14.4V.  Batteries older than 5/6 years are suspect and approaching end of life.  The battery is buried in the boot as you no doubt know.  Battery cables tight?  Cables at front jump point tight?

My thought process is that the fuel is OK, battery worth checking, and starter may or may not be engaging which could be battery, starter, cables or gear shift.

Check whether there is any difference if you are in 'P' or 'N'?  There is an starter inhibit on all gear positions except those two.  If the sensor on the gear selector is faulty it could result in a 'no crank' because it isn't detecting the correct setting.

[Batchelors]

Thanks for the reply x5
I would say the crank is a fast crank, but I will check all cables are tight in the morning and get battery voltage checked.
I've noticed the car tends to be worse when it's been raining like today.
I will check all that you have said tomorrow and get back to you.
Thanks for your help.

[X5Sport]

Fast crank eliminates cables (unless intermittent/loose) and starter motor but not the solenoid that engages it, and sounds like the battery is OK too.

Needs a 30i petrol owner to come up and cover the bits on that side of the engine.  Most on here drive oil burners or V8s!

Ignition switch is another suspect.  Same with both keys?

After that it starts getting complicated.  Might need a trip to  a BMW Dealer to see if any fault codes are  present.  There are so many sensors etc that could be upset by damp and stop playing nicely!

[Batchelors]

Yes exact same with both keys, I will still tighten up battery cables in the morning to eliminate that.
I will order a new fuel pump relay to eliminate that.
If neither works I will take it to local BMW.
Cheers mate

[mr angry]

If you are saying it intermittently cranks for short bursts and sometimes not at all then my money would be on the crank sensor but best get fault codes read to be sure.

[Batchelors]

Hi guys, just updating on car. I gave the fuel pump relay a tap and press and it's been starting first time since. I'm hoping that it might have come a little loose or something.

[X5Sport]

Probably worth replacing it then given how cheap they are.  Could be signs of it having a dry joint forming internally, or just slightly dirty pins at least.