Andy,

*stick it on a gas analyser the hc goes through the roof when the injectors play up*. HC is unburnt fuel and could also rise due to ignition or mechanical misfire.

I would expect to see high CO with an injector over-fuelling problem and low CO and low HC with an injector misfire. CO2 and O2 should not be disregarded when diagnosing a misfire. In the absence of fault codes, I would want to scope the injectors if a fuelling problem is suspected.

Regards

Pete M