Lemmy

About 10 days ago I posted about my Scoob (MY99 Turbo) failing its emissions test for its first MOT. The rear "secondary" cat has been removed, but I still have the main cat in the downpipe, so it should have passed the emissions test. However, it was giving 2.3 % CO and 0.937 lambda ratio. I suspected a failure of the lambda probe and took the car to my dealer yesterday for further investigation. The car was also occasionally stuttering on light throttle between 2000 and 3000 rpm, and seemed not quite as quick as normal.

The dealer put the rear cat back on and retested it - it failed, never had that before they said. So they replaced the lambda probe and it passed. They then removed the rear cat and it made hardly any difference at all to the emissions as the results below show:

With rear cat Without rear cat
Fast idle CO % 0 0
Fast idle HC ppm 8 9
Fast idle Lambda 1.004 1.007
Natural idle CO % 0.5 0.48

So, the rear cat seems to have very little effect on emissions. I also gather from the Subaru fitter that they now replace lambda probes when customers complain about misfires etc.

Alan

BugEyed

Lemmy

Glad you got it throught the test!

Interesting results for the rear cat. Had you taken it out for a quick thrash after re-fitting the rear cat to warm it up? If so, it appears to do very little other than strangle the power.

Duncan

Scott.T

iTrader: (2)

Nice One, Glad you got it sorted....

Lemmy

BugEyed

I drove the car to the dealer mostly at 50-60 mph which took about 30 minutes. By the time they did the final run without the rear cat the car had been at the dealers for 2 hours with perhaps 10 minutes fast idle (2-3000 rpm) running at most over that period. so I guess the cat was not particularly hot.

One interesting point made by the mechanic was that the UK300 doen't have a rear cat and that passes the emissions test.

Personally given my results I can't see any point having a rear cat. Like you say all it does is strangle the engine and it + backbox muffle the glorious exhaust note. Without the rear cat and backbox the Scoob certainly picks up better and is upto 10% quicker through the gears.

Alan

mutant_matt

The rear cat is supposed to "mop up" anything left after the main cat (which is uaually not a lot). You can remove it as you have found and still pass emmissions and the PPP cars don't have a centre cat to prove this.

Matt

scoobyboy

so lemmy after we sorted the emissions problem did you notice any difference in the performance. i seem to remember that you said there was a hesitation in it just wondered if it cured it really.
also when i done the cat test after replacing the probe the centre cat would have only been at normal temperature so there isn't any need to really get the first one hot as most people think. it seems to be able to cope quite happily with that.

Lemmy

Scoobyboy

I gather from what you are saying that you were the mechanic working on my Scoob. Thanks for the exellent service.

There is no sign of the stutter and the Scoob feels much quicker as well. It is now bl***y fast instesd of just fast as before! One other change for the better is that the glorious howl between 3-6000 rpm which had disappeared, has now returned after driving for about 50 miles. I also thing the inside of the tail pipe is less black than before.

Alan