I posted the following question on the Alfa155 forum and was kindly directed to post here as well. I hope someone is able to help...
I found this forum a few weeks ago and have dropped in a few times to search your tech archives. It's been very useful and I'd like to thank you all for sharing your knowledge. Anyway, I thought I should introduce myself before wading in with the questions
I'm actually here on a friends behalf - he doesn't have internet access but he has owned a '95 155 1.8 8v Silverstone for a couple of years now.
He's had several years (mostly) trouble free motoring from the car, but recently when it went for it's MOT it failed on the emissions test (9%!).
He tells me the car was always hard on fuel, with 24mpg the average regardless of how he drove it. However it passed it's MOT last year no problems.
My friend is a competent old-school mechanic but has always avoided working on the alfa because it was fuel injected and had an ECU. I, on the other hand am teaching myself mechanics with a fuel injected Pug 205 so I have few qualms about a bit of sensor diagnosis.
This is getting a bit long winded so I'll try and get to the point.
The plugs indicate the car is overfueling. The coolant temp sensor and throttle position sensor are working. The 4-wire heated oxygen sensor is reading a 12v constant on the heater wires and a fluctuating reading between 0.1v and 0.458v. There are no obvious vacuum leaks and the air filter is clean.
Oh, and the ECU is outputting a 4-4-4-4 when I connect a test light to pin 8 of the ECU.
What are we missing? Why such bad fuel economy and why such a high CO2 reading? Is the lambda sensor sending the wrong signal to the ECU and causing overfueling? Would a busted CAT give such high readings?
Any help or even just a fresh approach to this would be greatly appreciated. The more my friend and I try and figure this out the more confusing it seems to get. Thanks in advance,