Weird starting problem on 06 Mazda 3

[dnb]

I'm running out of ideas regarding an intermittent non-starting problem on my Outlaw's Mazda 3.

It sits several days between being used, and always starts first time from outside the house as you'd expect from a modern car. However, on 2 occasions now, it's been left at their destination (15 to 20 minute drive away) for at most a couple of hours and then it refuses to start. No cranking, but the fuel pump primes and immobilizer disengages - it's as if the battery has suddenly turned flat or the starter has become a dead short. I have got them home both times by jump starting the car with our Range Rover, and after that, the battery seems to recover after a couple of minutes of idle such that the car restarts without issue. Until the next time...

I have used a load tester on the battery and it pronounced it healthy. (But I have not load tested the battery just before the car is confirmed to be playing up - time travel is not in my gift)

I have checked the alternator is charging and the regulator is working.

I have not checked for excessive starter current yet - again, since I can't make the fault happen on demand, this test would not show a problem.

I have checked all the physical connections, relays, etc, and they look to be good.

I'm at a loss as to what the problem might be, and how to diagnose it, short of borrowing the car and driving it to work until it fails with a more permanent fault. It's perplexing - none of the usual suspects seem to be at fault.

Anyone have any ideas?

[stevieturbo]

If it doesnt crank and the battery is sound, then surely the starter or related items would be the obvious thing to check ?
Or main earth to starter etc ?

[dnb]

I believe I have checked the obvious things (battery, starter, relays, solenoid & cabling). There's nothing wrong with them when I look - although I have not managed to look at any of them when the car is in its failure mode because it's usually parked somewhere inconvenient.

[stevieturbo]

And is that the only location the problem occurs ? And is it the same location every time ?

Years ago a friend had an Evo, and if he parked it too near one of the electric companies transformers near a friends house, it fked his immobiliser up and the car wouldnt start. He had to two the car a short distance away before it would go again.

Although that was a very unusual scenario and a crappy clifford

[dnb]

It's been 2 different locations so far. No substations or phone base stations in the immediate vicinity that I've noticed. Plus we've always been able to jump start the car without moving it.

[stevieturbo]

If it jumps, then it sounds like a wiring/starter/charging/battery problem..

Try a new battery

[dnb]

I was resisting buying a new battery since the car can sit unused nearly all week and start fine, but after a short drive sometimes will not work at all. I do agree there's something weird going on, and I suspect the starter can get itself in a position where it won't engage, therefore uses excessive current to achieve nothing.