Spider Series 3 Cat removal

(also in Classic Alfa category)


I have removed the Cat on my Series 3 Spider and replaced the exhaust with a new full UK specification system (ie without a Cat). Does anyone have experience with doing the same? I read up on what the Lambda sensor does, which is to measure the percentage of oxygen in the exhaust, and fitted it to the new exhaust system. I know that cars usually only require the Lambda sensor if they have a Cat fitted, but the output from the Lambda is proportional and is fed into the main ignition ECU, so if I had simply left it off, the result would have been to richen the mixture. The car runs ok, but I'd just like to bounce this off a few of you before I put the car in for the MOT. (It did pass the MOT before, and that was with a bit of a smokey engine, since fixed, so I'm just being careful because it won't be at the same MOT garage this time, which is a shame.....)

In case any of you were wondering - My Series 3 is a US import, and hence the reason for the Cat. I do not legally need to fit a Cat over here because of the age of the car (1989). Of course, the price never came into it....!

I have dispensed with the cat on my series 4 spider. After discussing with my Alfa specialist I decided to disconnect the Lambda sensor altogether ( the alternative was to drill the exhaust just beyond the down pipe and weld on a nut to take the sensor). The result was that the ECU assumed a default setting for the missing sensor. We have measured the exhaust gases and they are well within the MOT parameters. There is no noticeable increase in fuel consumption in fact it matches the original spec for the car. The car does not seem to run slightly rich. The car passed its MOT without a problem.

If the ECU expects there to be a Lambda sensor, you are better off keeping it.

The Lambda sensor controls air/fuel ratios, without it the ECU may set to a default but it will run better in most situations with the sensor fitted.

I expect your Lambda sensor was located before the Cat, so it will operate exactly the same now as it did when the Cat was there.

Until the introduction of Euro3 specs in mid 2000 ECUs didn't monitor or care if the Cat was there or not.

Thank you for your quick replies. It would seem that I will be no worse off leaving it as it is then.

I should have stated that to keep within the required maximum distance from the manifold, I mounted the Lambda in one of the twin pipes before they join the single pipe (ie 4 - 2 - 1). Since it measures a percentage, it shouldn't really matter that I am only monitoring two cylinders. From what you have said, it won't make a lot of difference.

Just out of interest, is there anywhere on a car of this age (1989) to plug in a diagnostic tool? If so, where is it?

Thanks again,

Andy