hydrocarbons

[AJ]

I had the alfa mot'd this morning. the lamb reading passed on both normal and fast idle, but the hydrocarbons were quite high at 0.6 and the pass limit is 0.3
im running my own maps based on the standard fiat coupe 194.04 map with only slightly modified fuel and idle speed maps.
I guess the high hydro carbons is related to the (lack of) cat, is there any way I an reduce these other than fitting the cat?

[na15575]

hi
in all the cars that i have own i never change the cat no need exept the broken one
Try to reduse the fuel pressure to 2.0 or 1.8 bar just to pass the limit and then...

[AJ]

Thinking about it I think the 0.3 limit and the car's achievement of 0.6 is for CO. Shame I didn't get the print out to confirm.

I don't have a cat fitted, and do have a 255l/p/h fuel pump but standard fuel pressure regulator. Changing to a higher throughput pump did make it run richer on the standard regulator.

I guess the high CO is thanks to the lack of cat to do convertin the CO to CO2.

[WhizzMan]

HydroCarbons are unburnt fuel. CO has no Hydro atoms in it, so it can't be CO. It seems your mixture is okay, but your spark might not be up to par. Unless you've changed cam profiles or are spooling an insane amount of turbo pressure (I doubt that, since the engine isn't under load during the test) and you're flushing out mixture through the exhaust before you close the exhaust valve.

Or is your second post correct and it's not HC but it is in fact CO? In that case, lean it off a bit just for the test, your engine will run worse, but you just might pass the test. Fitting a cat will work for certain in this case.

[AJ]

Well, I've successfully consufed myself! I'm sure it passed 2 out of the 3 checks. I'm just not 100% sure what it failed on - the HC or the CO.

The lambda reading was good

Standard cams, uprated fuel pump, no cat, the map are the main factors that have been changed which will affect fuelling.

If I lean it off to reduce CO, is there a maximum lambda value limit?

It's not an issue for me, but I guess what I'm trying to achieve is to get it through the MOT emissions with no cat, or to see if it is possible.

[cuore_sportivo_155]

1.000 +- 3% is the limit here, not sure about the uk though, but think it's a european thing....

BTW, the q4 is not in the MOT computer so if it fails the emissions test it should be subjected to a test for non-catalyzed cars... have a look on the forum, there's plenty said about that...

[AJ]

I think there is lambda limit which sounds about right. I don't have a Q4, I have a 145 with a Fiat 16vt. I guess I could always claim it is from a Q4

[cuore_sportivo_155]

ah, in that case you need the rules for the 155 no doubt.... cat might be required...

[AJ]

The emissions would follow the engine, but would the cat follow the engine or car

[wrinx]

Engine I'd have thought...exhaust being part of the engine.

wrinx

[na15575]

hi
the limit of 0.3 is for the co
sorry that i didnt notice it to the first post
if the engine is working good you dont need cat to pass the test
if the co is out of limit then the ecu dont measure the correct amount of air for some reason this a law for co.
check for air leaks
check the map sensor(air pressure)
try to play with the idle up or down
and after that you can ajust the co one way from the skrew near to the map sencor
and secont from the ecu via diagnostic eguip like examiner

but try to lean it is good for both co and HC but only for the test you can damage the engine if you live it for long

[AJ]

I thought the cat converted CO to CO2, so it would have some effect on the CO reading if it isn't present?


It does idle quite high, ~950 when warm, I guess I could reduce this. This was done in an attempt to help stop it stalling when hitting the clutch (lightened flywheel, internals).

I don't think I have any air leaks, it has a steady idle at 14.7:1 and the map sensor was reading correctly when I had checked it previously.

I don't have a CO screw, I am using the Fiat Coupe ECU.

Perhaps I'll just have to give in and fit the cat should I have an issue in coming years.

[WhizzMan]

The cat does convert (some) CO to CO2, and reduced NOx emissions as well. If it's just CO, you could lean it off a bit in your custom programming (for MOT only, you'll want it on lambda 1 for light loads and rich for full power). Make certain all your sensors are working and you have no air-leaks before you fiddle with the tuning.

By the way, giving the engine some decent italian tuning and making certain it's well up to temperature tends to give you lower CO ratings. Most of the carbon deposits have burnt off then, the fuel evaporates good with the high temperature in the engine and you'll have less partially burnt fuel in your exhaust gasses. It only works for a little while, but it'll be good enough to pass MOT in quite a few cases.