I’m having intermittent starting issues with my car. ie it’s fine for long periods but now and again wont start up.

Example today when I drove somewhere, got back in the car – it wouldn’t start. Called the AA, by the time the AA guy arrived the car started perfectly.

Mechanic tested the battery and it was ok.

Seems like its trying to turn over, but doesn’t quite have enough oomph to start. However after it was left for an hour or so waiting for the AA, it started fine. The battery was new last year.

Any ideas what could intermittently be causing this – dealer couldn’t find anything wrong in the fault codes, or lack of them? The car is a BMW.

Dodgy connection on the positive wire between the battery and the starter motor? corroded possibly, or loose/failing connection? or possible the same problem on the main earth cable from the engine block to battery?

or could be a knackered battery even though its only a year old (they do fail sometimes – especially if its a halfords own brand battery) – new (branded) battery is probably cheap, so might be worth a try and see if its ok

Had a van with these exact symptoms. Traced it to a dodgy earth connection.

I had this on a TDi, only when it was warm – it was the cam position sensor.

Petrol or diesel?

When I had that with mine years ago it was the glow plugs on an old diesel.

Has it been left sitting since march and only just started being used again?

Dad has similar on his van.turned out to be the battery

Is it a Diesel?
I’m not familiar with BMW diesel engines but I had a Mazda 6 that would do that.
The cause was the DPF system. If it didn’t complete a re-gen cycle the diesel flushed onto the DPF would end up in the sump, causing the oil level to rise to the point where it would either self fuel. Or if stopped for a short time would struggle to turn over due to excess oil/diesel that had migrated to the top of the pistons causing hydraulic lock.

The car is a 320 diesel. Been used intermittently since March – but battery fine according to the AA. The battery was new last year.

There are no other symptoms – just the once in a while starting issue!

The battery was new last year.

I’ve had a battery fail that was ‘new last week’ at the time. If its testing as ok thats fine – but the newness of things doesn’t rule them out.

I suppose the obvious thing is a worn starter motor

Easy way to prove a bad battery earth (the resistance only increases under high load so you can’t measure it easily) is to put single jump lead from the battery negative so an engine lifting eye, or perhaps a seatbelt bolt or door catch if the battery is in the boot. This gives a good earth for diagnosis purposes.

As above and also on a BMW 3 series. Cam position sensor. You need a code reader.

same sort of thing happened to us a couple of times. the car would start fine but even after a short trip to the shops it wouldnt start but after a while it would. Called the AA and they said it was the battery being low with the car hardly moving for the last couple of months once the car had sat for a while the battery had recovered enough to start the car. I’ve been popping it on charge for a while each week to top it up

thanks – Its been in before but apparently no fault codes recorded.

Back to a dealer it goes then!

I had a subaru that wouldn’t start if the interior of the car was very hot, like on a sunny day.
When you turned the key, all the lights would come on as normal, but it wouldn’t make any attempt to turn over.
Sit with the door open to let it cool off a little, it would make start normally.
Or you could bump start it if you were on a hill.
Cold weather it always started.
Weird.

Sounds like you need to get a new bike.

Had a similar thing recently. Turned out to be the electrics in the starter motor unit. Dodgy relay. Had to replace the whole lot but got a reconditioned unit for not much. Not a safety critical part so not bothered by second hand part.

dyls
Member

thanks – Its been in before but apparently no fault codes recorded.

Does it record them though?
If you have/can get a reader check it when it won’t start. If you take it to a dealer later presumably it’s driving fine then and so the code won’t show, unless it stores old ones to download later?

Ahh…. I thought it stored old fault codes, but yes it makes sense, if the car is driving fine when it was at the garage, then no fault code showed up – which is what the dealer told me.

Might have to describe the problem to them then.