Interesting emissions test results

[dnb]

Just had my garage check the Griff's emissions. This is the first time it's been looked at independantly since the VEMS ECU was installed and the ACT exhaust put on. (No cats were in for the test, as I wanted to assess the engine on its own.)

We just did a natural idle test:
Lambda: 1.002
HC: 550 ppm
CO: 1.1%

It's good to see the lambda being spot on - and even agreeing with the ECU's wideband sensor readings, however the HC reading is a lot higher than I expected. CO is about right for the engine, but I'd obviously like it a bit lower. With cats, it should be no problem for the car to pass the test easily.

What mechanical things start to affect the HC readings but not the others? This, I think is the next thing I need to sort out.

[GreenV8S]

Hard to say. CO suggests incomplete combustion i.e. not enough oxygen available, HC suggests partial combustion i.e. mixture that hasn't lit, possibly from a weak spark or just crevice volume. Both together would suggest excessive fuel or poor air/fuel mixture preparation.

[dnb]

Probably that dodgy FSE regulator... Dropping the fuel pressure too much at idle and causing bad atomisation.

[that daddy]

DNB, high HC can be all sorts ,air leak,faulty HT leads knackered spark,ignition timing,spark plugs,valve trouble(poor sealing or burnt)burning oil,low compressions,badly clogged injectors,etc etc or a combination of some of these, your right those hydrocarbons are a tad high alright.was the car stinking hot when this was checked,had it been driven (correct),or was it just warmed from cold without driving(not the correct way to do it).

[dnb]

Fairly sure it isn't the ignition system - all this is new and over-specc'd.
Not injectors - again, they're new.
Compression was good when last tested in the summer.

The car had just had a couple of new tyres, so hadn't been warmed. The gauge showed 75C so the car had only just turned on closed loop lambda control.

Best guess is timing is set wrong or there's some valve trouble - likely on a 100k+ mile engine.

Either way, it's not a major worry - the new ECU is going to be capable of getting the car through a standard emissions test, so I don't have to rely on the "Griff and Cerb" clauses in the MOT book.