Alternator woes

[CRC]

You could well be right.

If one or more diodes on the alternator has failed, that would explain the big parasitic draw when the car is switched off.

With the alternator unplugged, used a multimeter on "diode test" setting to check between the power terminal on the alternator and the alternator chassis and see what you get.

There are several YouTube videos showing how to do this.

[deemdoubleu]

I have done some more diagnostics:

Re-connected alternator feed.
Monitored current on battery negative cable.
Current is not high - settles down to 100mA roughly in that region.  Not sure why it was extremey high previously - very strange.
I have a spark. Tested with one cylinder spark plug against engine block.
I have fuel. Disconnected fuel line at engine and plenty of fuel flowed out. Not dry.
I have monitored cam shaft rotating when starter motor engaged looking into oil filler cap
I have checked all fuses. All appear to be good.
I have rotated all similar relays in main engine compartment fuse box.
Yet, when I try to start engine, it won't fire.

Could it be crank or cam sensor - would I get a regular spark if either of these was U/S?

Could it be injector drive - anyone know how to check without taking top of engine apart?

I have it booked in with a Honda specialist in a few weeks (he must be busy).

I will try to check for fault codes next but any other ideas?

[CRC]

This may sound crazy, but how long have you tried cranking the engine for?

You seem to have done all the normal checks - fuel, spark etc, but you could try cranking it for longer?

There's a little known but very common scenario where cars that have been left standing for a long time or have been started briefly and then stopped just don't want to start again and spin over so fast that it seems like there's no compression or that the spark plugs have been removed.

The reason is that the compression rings need to have a film of oil on the bores to seal properly as they sweep down the bores.

This can be caused by a brief cold start and stop, where the injected fuel sits on top of the cold  piston and doesn't evaporate, so it leaks past the rings and washes the oil film off the bores, or, purely by leaving the engine long enough to allow the oil to drain naturally down.

The cure is to to keep cranking the starter with the throttle wide open, and eventually the action of the crankshaft spinning throws enough oil on to the bores to allow the compression to return and the engine to fire, normally on one, then two then all four.

Once all four have chimed in, warm it up and it's fine again.

I've known this happen so often on so many makes of car.

Probably not, but the speed of cranking will give you a clue .....

100 mA parasitic draw is still a bit high, below 50 mA is the accepted norm.

[deemdoubleu]

I've cranked it for a good few seconds multiple times but I haven't depressed the accelerator pedal.  Will give it a try thanks.  Funnily enough, the last time I remember it running was a brief cold start while I backed it up a few feet and then switched off so your comment might make sense.

[deemdoubleu]

This may sound crazy, but how long have you tried cranking the engine for?

You seem to have done all the normal checks - fuel, spark etc, but you could try cranking it for longer?

There's a little known but very common scenario where cars that have been left standing for a long time or have been started briefly and then stopped just don't want to start again and spin over so fast that it seems like there's no compression or that the spark plugs have been removed.

The reason is that the compression rings need to have a film of oil on the bores to seal properly as they sweep down the bores.

This can be caused by a brief cold start and stop, where the injected fuel sits on top of the cold  piston and doesn't evaporate, so it leaks past the rings and washes the oil film off the bores, or, purely by leaving the engine long enough to allow the oil to drain naturally down.

The cure is to to keep cranking the starter with the throttle wide open, and eventually the action of the crankshaft spinning throws enough oil on to the bores to allow the compression to return and the engine to fire, normally on one, then two then all four.

Once all four have chimed in, warm it up and it's fine again.

I've known this happen so often on so many makes of car.

Probably not, but the speed of cranking will give you a clue .....

100 mA parasitic draw is still a bit high, below 50 mA is the accepted norm.

CRC you are a genius.  The car is now running fine.  I depressed the throttle to the floor and cranked it.  It took as number of attempts and about a minute of cranking in total but sure enough it started to cough and splutter and eventually fired up.  I let it stabilise and after gaining a bit of confidence took it out for a run to warm up fully.  Everything fine.  MPG as normal > 60mpg so I hope no lasting damage.

I cannot thank you enough, you have saved me a lot of grief and restored my faith in the Honda brand.  Also checked alternator and it is fine (charging over 14V) so the current drain must have been either an error on my part or some strange condition it was in.  I will keep my eye on that.

Once again, thank you CRC!

[ColinB]

In some circles, this is known as "clear flood mode" (try googling that phrase). Most often happens when a modern engine is started briefly and stopped soon after. When I came across this with a previous car, the breakdown guy advised that if you need to move a car a short distance (say re-parking in a slightly different place on the drive), always do it by driving round the block.

[deemdoubleu]

In some circles, this is known as "clear flood mode" (try googling that phrase). Most often happens when a modern engine is started briefly and stopped soon after. When I came across this with a previous car, the breakdown guy advised that if you need to move a car a short distance (say re-parking in a slightly different place on the drive), always do it by driving round the block.

Amzing isn't it that once you know about something, you find it referenced everywhere!  I had honestly never had this issue or heard about it in over 40 years of driving.  I had heard the term "flooded engine" many times but never though that in a modern Honda engine it would be a thing.  The crazy thing is how it persisted for 5 weeks.

[CRC]

My brother was a Honda mechanic for many years and they called it the "paper shop problem", as it often happened on cold frosty mornings when an early shift worker started his car fine, then drove a few hundred yards and stopped to get his paper and found that the car wouldn't start again when he came back out.

Modern fuel injected engines don't have a "choke" as such, but monitor the temperature and inject more fuel to give a rich mixture until the car is up to temperature.

If the engine is then stopped before the pistons are warm enough to evaporate the unburnt fuel that's been squirted in, it remains as a liquid and that washes the bores of oil.

If I have to briefly move a car, I'll always take it round the block to make sure the pistons are warm enough to evaporate any fuel that's left when I stop it.

By holding the throttle wide open, you are allowing maximum air flow to evaporate injected fuel while compression is starting to build up.

You won't have done any damage ....