E30 Zone

Hi


Im having some trouble getting my car through the mot, due to high HC reading.

Some background info:

I had two 318is, one was my daily while i fixed the other one up. My daily had a rebuilt engine in when i bought it, so when it came to selling it i swapped the engines over. The old daily sailed through the mot's.

Now i only have my project car, but when it came to going through the mot it failed on high HC. So i took the cat off to have a look and it all seemed fine, but the pipes before and after were very sooty. Ive also checked for vacum leaks but the werent any.

Anyone got any ideas??

WHAT CAUSES HIGH HYDROCARBON

1. Improper Ignition Timing 2. Defective Ignition Components 3. Lean Fuel Mixture
4. Defective Catalytic Converter 5. Low Cylinder Compression

and other s**t i can not remember at this time

Ideally need to know all the gas test results to give any kind of reasoned answer, but rich or excessively weak mixture*, or an ignition problem will all give high HC.
What is the build date, or first registration date of the car, and of the engine that is in it now?
Are you in the UK?

*If the mixture is too weak to burn properly, unburnt fuel will pass into the exhaust.

Im living out in sweden so no chance of a friendly MOT'er, they're very stricked-i failed once for not having an aerial !!!

Both cars are 1990, the engine was rebuilt about 4 years ago.

Here's the MOT info:

CO-0,1 (0,5)
C0 2500 0,1 (0,3)
HC 293 (100)
LAMBDA 1,01 (0,97-1,03)

The bracket numbers are the limits.

The CO and LAMBDA are all good.

Can't make sense of the second line. Is that CO2? If so, what's the 500 part?

Yeah im not too sure what CO2500 is, but thats all the figures on the sheet. The CO2 isthe first line, The CO is all good its just the HC.

At fast idle speed maybe 2500rpm?

That makes total sense

I know you said you've checked for vacuum leaks, but have you checked all the breather hoses very carefully? They are very prone to splitting in and around the inlet manifold, i have simplified mine and run it around the outside of the inlet manifold for easy maintenence. If one is split or perished the engine can draw air in after the airflow meter, weakening the mixture. (as Brian said, mixture weak = unburnt fuel = high hydrocarbons)

I thought I'd update this, the problem turned out to be the lamba sensor. I replaced it and it sailed through the MOT.