CO & HC Readings - possibly one for Brian

[capri_rob]

Seem to remember a thread on this recently where zoners posted their MOT stats but can't find it

Regardless of what is needed to pass the MOT what is considered healthy CO and HC readings for an M20B25 in standard form ?

And if the readings are not considered "good" even if they are an MOT pass what can be done to improve them being as tampering with the AFM is a no-go.

Mine as of yesterday were 0.3 CO and 849 HC - I have no idea whether this is good or not even though it was well within MOT tolerances.

[PG325]

My last MOT stats were 1.04% CO against a max of 3.50% and 137 PPM HC against a max of 1200 PPM.

I would say your CO is low, possibly running lean and your HC are high, but as your on gas your figures may be spot on.

Mine is an 89 325i and at a very steady 50 MPH on an average speed camera restricted M4 will do high 30's, I know this as I filled her up in Bristol and then for a laugh filled it at the next service station, however having a bit of fun around the country roads near Castle Combe returned mid 20's.

[capri_rob]

I'm not on "gas" - Fuelly is a US site so just referring to Gasoline

I need to dig out last years results - I'm sure it was said to be running lean then but the head has been off and rebuilt since - the reason for the lean running last time was a loose fitting AFM bellows which was allowing too much air in but everything has been double checked and all the seals/hoses/clips replaced since.

Can incorrect valve clearances affect these figures as I'm pretty sure these need adjusting to cure the slightly rough idle

[Brianmoooore]

Limits are 3.5% CO and 1200 ppm HC, as said above, and PG325's results are about the going rate for an E30.
0.3/849 indicates an engine that is probably running lean and miss firing (remember, these are only idle figures). A better diagnosis could be made if you have the results for any other gases - didn't you get the gas results sheet with your MOT?

[capri_rob]

The test equipment used is an Innova 2000 whatever that is and there is no mention of any other gases on the printout.

Last year was 0.22% CO and 119 HC - that was pre-head rebuild. I take it a high HC level is unburnt fuel in the gases ?

It does have a rough idle like its misfiring but as soon as you give it the slightest throttle the misfire disappears and it runs very smoothly. I have put this down to the valve clearances needing checking and resetting as this is the only thing that hasnt been done since the head went back on.

As soon as its Taxed its going to danthe for a checkover to see if he can diagnose whats wrong but any pointers to check would be useful.

[Andyboy]

Mine (1989 E32) are 0.40 CO and 141 ppm. Valve clearances would indeed account for a higher than normal HC reading. Your CO reading is okay though - you could richen it a touch on the AFM screw once you've sorted the HC's.

HC is Hydrocarbons, unburnt fuel in Parts Per Million (PPM). As an example, a catalysed car limits are 0.30 idle, and 0.20 on fast idle with 200 ppm.

[capri_rob]

Thanks Andy

[cjdonny]

Hijack

Got my 318 IS last year with full mot

but i called round at my local mot test station before putting here away in the garage

seemed to be running rich

results were

CO: 0.353 FAIL/0.200% Limit
HC: 69 PPM PASS/200 ppm limit
Lambada: 1.124 FAIL/0.970-1.030 limit

[Andyboy]

Lambada: 1.124 FAIL/0.970-1.030 limit

OLE!!

[cjdonny]