Cylinder not firing on startup

[domV8]

When I start the car up from cold, it seems that (at least) 1 of the cylinders isn't firing initially - car vibrates very slightly (normally smooth) and there is the occasional (almost unnoticeable) jolt on acceleration.

Goes after about a minute, back to its normal smooth self.

Car runs aftermarket ECU with coilpacks - not had any problems for 3-odd years, just started happening.

Any ideas on common causes for this? My complete guesses might be..:

- dodgy sparkplug
- HT lead issue
- sticky valve
- lifter taking time to pump up (but no tapping sound?)
- injector issue
.......

The crux of it it that it resolves itself within a minute - might indicate something to those with more technical knowledge than I...

Unfortunately don't have any tools to test things etc, so trying to eliminate/pinpoint causes via theory at the moment...

Thanks,


Dom

[QBee]

add plug extenders to your list
you can at least find out which cylinder it is by measuring exhaust manifold temperatures with a digital laser thermometer while it is misfiring.
You will need one of these:

linky

to state the obvious, the non-firing port will be about 100 degrees cooler on the exhaust manifold than the others, at about an inch from the manifold gasket.

Edited by QBee on Friday 3rd July 14:42

[Trevor450]

Add checking your coolant to that list. A slightly weeping HG may be a cause of this symptom too as moisture in the cylinder would cause a slight misfire until it burnt off.

[Dr Mike Oxgreen]

Add coolant temperature sensor to your list. (The ECU one - I assume the ECU you're running still connects to the same sensor).

My car used to run horrendously rich on a cold start, to the extent that at least one cylinder was slow to join the party. New coolant temperature sensor has solved the problem completely. Make sure to get one with the nut made of brass, not plastic.