hi i have a my2000 uk subaru and when i had print out of emmisions data the hc were reading 0 co was 0 and lambda was 1.020 what would cause hc to be so low

 

Cause of low HC is good combustion!

HC is unburnt fuel (fuel and oil is HC, short for hydrocarbon). CO is carbon monoxide - from combustion with lack of oxygen; the lower the better.

However a reading of zero is a bit odd; To me it suggests the gas analyser was zeroed with the probe still up the exhaust pipe! (it should be removed from the exhaust pipe when auto-zeroing) or the water trap needs emptying.

Basically put, the readings are wrong.

 

co machine was all ok at time and calibrated with pipe out

 

something wrong with that machine, did they have the probe shoved up the exhaust of the right car?

Tony

 

yeah machine ok thats why i posted about it as i found it strange but i know machine is fine

 

The machine is not fine! Probably a blocked filter on the back of the emissions machine. The readings suggest the car is producing only oxygen and nitrogen!

 

i use this machine everyday for mot testing and it reads ok on other cars just mine

 

So you think you're car could produce no hydrocarbons or CO at all? A good impreza with good cat and everything in order will hit about 12-20 on HC and about 0.08-0.15 on CO with the lambda in the allowed limit.

Correct me if I'm wrong, but zero HC, zero CO and 1.02 lambda means a pass? If so I would celebrate! It could just be an extremely good cat, but I don't see it. Snapping open the throttle should take it out of close loop and drop the lambda to around 0.9 on average with CO up in the 3-4% range if you pump the throttle once a second or so.

The only time I've seen your problem is when the one or other of the charcoal filters on the back needs replacing.

 

where abouts are the charcoal filters at the back are they needed or can i disgard what is the canister at front is that not a charcoal filter

 

I think Zen is talking about the charcoal filter on the testing machine, not the car! ROTFL

 

was the engine running for the test???

 

i test cars all day at work and the machine reads ok and the hc test is always calibrated before test i have posted this to see if anyone knew what would cause this i will post some pic to show

 

So what is the actual problem? Your car passes the emissions test, and presumably runs okay, what's the issue?