I asked this question a couple of months ago, but have learned a few things since. Problem is still there though. Here is the typical scenario:

- In the mornings when the temperature is at 2*C or less, most likely when it has been colder at night previously, there is a mis-fire on start-up.
- From here, the revs will limit at 3000rpm and it lacks power.
- Apparently, it seems to me as though it reaches running temperature quicker than usual, for example within one mile rather than three miles. (FURTHER EDIT: despite thinking this is less of an issue than I thought on testing it out, it can be a mile difference in warm up temperatures. Further info posted later)
- I need to re-start the engine to get it to reset itself to run normally, but even at running temperature I still need to have been running at it for another ten minutes or so.
- Often seems to re-start better, if with car travelling, I turn off ignition and restart with the clutch, but this could be coincidental.

Oil levels are always fine, battery has been replaced, spark plugs replaced, full HSH, last one at 147k last week. Car runs perfectly otherwise.

If cold at night, after a normal day, less of an issue which suggests the car needs to be cold for a period of time. Over 3*C and car always starts and runs perfectly.

The key symptom seems to be the mis-fire on start up in freezing point weather. Service last week picked up the mis-fire and suggested spark pligs (which were admittedly grotty), but why does it warm up more quickly than it does under normal circumstances?

Problem with coolant? HT leads? Gasket issue? Sensors? Something else?

 

Mmm thinking. The S doesn't have ht leads as such does it? otherwise I'd have said they may have shorting. If it was coolant or a gasket would you not be loosing coolant and see this reflected in the topup bottle level, kinda swaying towards a sensor but which one.

 

Just thinking........... air pump?

 

What about the coolant partially freezing somewhere in the system causing a blockage and preventing the coolant circulating properly hence the rapid warm up cycle.

 

I would replace the coolant temperature sender and go from there.

I'm thinking the enrichment program may not be running at start up, and one cause is incorrect water temperature info.

 

Also, you'll know if the airpump is coming on or not, if it isnt you wont get the 'tsssh' noise and likely a CEL light.

 

That really is one where you need some plug in diagnostics, and someone who knows what they are looking at...

I think Steve is along the right lines though.

 

Thanks for that. Is that a reasonably straight forward job to do or is it something that involves pulling far too much apart with an outlay on equipment? Quite happy to look at it myself and would also be interested in knowing the price and possibly the part number as I'm guessing that I go strarght to Honda.

Experimented with the warm up mileage and as is often the case, it's never quite as bad you initially think. At 2*C it warmed up at 1.5 miles (Saturday) and at 5*C (Sunday) it warmed up at 2.0 miles, a minute or two later. Would need to check again in the future to be certain. Had wondered about the coolant, but seems fine.

 

The plot thickens...

Another cold day, another mis-fire, CEL and limit to 3000rpm until at running temperature. The 3 engine temp blocks came on 1 mile earlier than a standard morning which still confuses me. Should I just replace the coolant I ask myself?

I decided to ring the dealer and spoke to the service manager who owns an original S2000 too. Turns out that the message he left for me when I picked up the car after my service didn't get to me. The CEL code showed that there is a problem with the ECMU and that if it happens again, to come back in and get it code checked. If it's the same again, new unit required - wonder how much that is and should I fit it myself if accessible?

 

ECMU? think he means ECU. If it did need replaced they can for around £100 2nd hand, they would probably want 8 times that new.

Could be a long short but its not unheard of (i remember doing this with a civic that came into my mates for a tune and it worked), sometimes the pins on the ECU have corrosion on use some contact cleaner and a brush.

Simple 5minute job really.

But somehow i doubt the ECU would feck up

It might help.