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[Lazydocker]

The battery on the car is years old.. I think it might just be tired out?

Do you have access to a proper battery tester?

Sadly not

Local parts place will probably have a drop tester (assuming it's not ECP... Don't know about them)

[Marks DTM Calib]

Symptoms don't point to a battery fault at all.

Starts fine when cold, wont start when hot....most important question is if the engine turns over ok, if it does, battery is not the issue.

[Lazydocker]

Symptoms don't point to a battery fault at all.

Starts fine when cold, wont start when hot....most important question is if the engine turns over ok, if it does, battery is not the issue.

I agree. But I have seen them where the ecu is not seeing a charged battery (cranking voltage too low) and causing issues, hence my suggestion of trying jump leads.

I'd still be looking at wiring faults over a battery. I suspect that a new battery won't cure it as with jump leads there is around 14V instead of 12V (obviously), offsetting the drop that is being seen.

[Marks DTM Calib]

Remember that the ECU internals do not run at 12V, they will be most likely 3V3 supplied by a controlled DC-DC, hence if the volts available is enough to crank, its more than enough for the ECU to run without any issues 

[Lazydocker]

Remember that the ECU internals do not run at 12V, they will be most likely 3V3 supplied by a controlled DC-DC, hence if the volts available is enough to crank, its more than enough for the ECU to run without any issues 

Yes... But it's seeing 11V and having a hissy fit because of it. connect jump leads and it starts fine. Never understood why but seen it before. Last one was a ground fault. Previous was starter internals.

[Nick W]

The battery on the car is years old.. I think it might just be tired out?

Do you have access to a proper battery tester?

Sadly not

Time you splashed out £25 on one then!

[Gaffers]

Remember that the ECU internals do not run at 12V, they will be most likely 3V3 supplied by a controlled DC-DC, hence if the volts available is enough to crank, its more than enough for the ECU to run without any issues 

Yes... But it's seeing 11V and having a hissy fit because of it. connect jump leads and it starts fine. Never understood why but seen it before. Last one was a ground fault. Previous was starter internals.

It could also be the high fluctuation of voltage in a short period you get with a knackered battery,  I could see that affecting the 3.3 or 5v being supplied to the ECU.

[JasonH]

Here are a few thoughts (from BMW experience):

Corroded connector at the ECU caused by water collecting there.
Dodgy ignition / engine management relay.
Sticky starter motor causing a big battery voltage dip.
BMW ECU's (of which some are definitely Bosch) really don't like being given below 12V, some will log under voltage faults others will give spurious fault codes.

[Marks DTM Calib]

Remember that the ECU internals do not run at 12V, they will be most likely 3V3 supplied by a controlled DC-DC, hence if the volts available is enough to crank, its more than enough for the ECU to run without any issues 

Yes... But it's seeing 11V and having a hissy fit because of it. connect jump leads and it starts fine. Never understood why but seen it before. Last one was a ground fault. Previous was starter internals.

Sorry, disagree here.

The original symptoms state:

I've worked out the issue is a "hot start" problem. When you start the car from cold, it almost catches, then doesn't. but the next time you turn the key, it's off - no repeated cranking.

and

The car will then run all day long without missing a beat. But when you turn it off, having got up to temperature, it WILL NOT start - it just cranks over and over

Which, given that the worst case for battery terminal volts is after a period being stood and cold start, goes totally against the diagnosis some are stating. This is further backed up by the fact that even if there was a very large initial voltage dip whilst the starter engaged, the ECU would be up and running within 1-2 seconds after this assuming a watchdog event on the processor had occurred (it wont, there is more than enough smoothing caps and holdup in these units to ride through a few milliseconds of extraordinary voltage dip).

Remember all, test and diag is the key to effective diagnosis, leave the willy nilly part changing to the professionals lol 

So questions have to be

1) Is it turning over ok (removes the battery from the equation)

2) If you continue to crank does it start (further removes the battery from the equation)

My money is still on an electronic component which is struggling when hot, classic symptoms of crank sensor actually and giving a few more volts is resulting in a few more rpm and just getting over the threshold of speed where it works. Sadly this is also the symptoms of a goosed Siemens ECU! Change the battery and you might mask the issue for a few months until the morning temperatures drop again. 

So much more diag needed

[Lazydocker]

Remember that the ECU internals do not run at 12V, they will be most likely 3V3 supplied by a controlled DC-DC, hence if the volts available is enough to crank, its more than enough for the ECU to run without any issues 

Yes... But it's seeing 11V and having a hissy fit because of it. connect jump leads and it starts fine. Never understood why but seen it before. Last one was a ground fault. Previous was starter internals.

Sorry, disagree here.

The original symptoms state:

I've worked out the issue is a "hot start" problem. When you start the car from cold, it almost catches, then doesn't. but the next time you turn the key, it's off - no repeated cranking.

and

The car will then run all day long without missing a beat. But when you turn it off, having got up to temperature, it WILL NOT start - it just cranks over and over

Which, given that the worst case for battery terminal volts is after a period being stood and cold start, goes totally against the diagnosis some are stating. This is further backed up by the fact that even if there was a very large initial voltage dip whilst the starter engaged, the ECU would be up and running within 1-2 seconds after this assuming a watchdog event on the processor had occurred (it wont, there is more than enough smoothing caps and holdup in these units to ride through a few milliseconds of extraordinary voltage dip).

Remember all, test and diag is the key to effective diagnosis, leave the willy nilly part changing to the professionals lol 

So questions have to be

1) Is it turning over ok (removes the battery from the equation)

2) If you continue to crank does it start (further removes the battery from the equation)

My money is still on an electronic component which is struggling when hot, classic symptoms of crank sensor actually and giving a few more volts is resulting in a few more rpm and just getting over the threshold of speed where it works. Sadly this is also the symptoms of a goosed Siemens ECU! Change the battery and you might mask the issue for a few months until the morning temperatures drop again. 

So much more diag needed

Agree with this. But... Explain why connecting jump leads has cured the problem twice?

[Marks DTM Calib]

I already have offered a possible......

[Lazydocker]

Symptoms don't point to a battery fault at all.

Starts fine when cold, wont start when hot....most important question is if the engine turns over ok, if it does, battery is not the issue.

One of the first posts says it wouldn't start from cold, stick jump leads on and it was fine.

We are in agreement that this doesn't appear to be a battery fault... I suspect a new battery would cure it in the short term but just mask the issue.

[JamesV6CDX]

Would the crank sensor cause the p060c code?

I considered crank sensor. But was wary because, when hot (without jump leads) the engine turns, doesn't fire, logs p060c code

When hot WITH jump leads, it starts so well and so quick, it's like it's not even had to turn over!

Is there a way to test the crank sensor rather than change it in hope?

[JasonH]

To test the crank sensor you really need to get an oscilloscope on the signal from it.

If the waveform is clean and strong when the second battery is connected but not when it isn't then you have nailed the problem. If there's no change to waveform with or without a second battery or hot and cold  then the crank sensor is probably fine.

If you Google Fiesta and crank sensor you'll find it's not an uncommon failure. If they're not expensive it might be cheaper to change it than try to test it.

[Gaffers]

Remember that the ECU internals do not run at 12V, they will be most likely 3V3 supplied by a controlled DC-DC, hence if the volts available is enough to crank, its more than enough for the ECU to run without any issues 

Yes... But it's seeing 11V and having a hissy fit because of it. connect jump leads and it starts fine. Never understood why but seen it before. Last one was a ground fault. Previous was starter internals.

Sorry, disagree here.

The original symptoms state:

I've worked out the issue is a "hot start" problem. When you start the car from cold, it almost catches, then doesn't. but the next time you turn the key, it's off - no repeated cranking.

and

The car will then run all day long without missing a beat. But when you turn it off, having got up to temperature, it WILL NOT start - it just cranks over and over

Which, given that the worst case for battery terminal volts is after a period being stood and cold start, goes totally against the diagnosis some are stating. This is further backed up by the fact that even if there was a very large initial voltage dip whilst the starter engaged, the ECU would be up and running within 1-2 seconds after this assuming a watchdog event on the processor had occurred (it wont, there is more than enough smoothing caps and holdup in these units to ride through a few milliseconds of extraordinary voltage dip).

Remember all, test and diag is the key to effective diagnosis, leave the willy nilly part changing to the professionals lol 

So questions have to be

1) Is it turning over ok (removes the battery from the equation)

2) If you continue to crank does it start (further removes the battery from the equation)

My money is still on an electronic component which is struggling when hot, classic symptoms of crank sensor actually and giving a few more volts is resulting in a few more rpm and just getting over the threshold of speed where it works. Sadly this is also the symptoms of a goosed Siemens ECU! Change the battery and you might mask the issue for a few months until the morning temperatures drop again. 

So much more diag needed

Agree with this. But... Explain why connecting jump leads has cured the problem twice?

[Gay voice on]

Is it becoz da batteries like their nipples to twisted?