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[Doctor Gollum]

Any performance issues BEFORE you first removed the original 3.2 cats?

[Enceladus]

And what fault codes did you get with the original 3.2 cats? You mentioned the light was permanently on. Was it P0420 and/or P0430?

And did you ever re-position the 2nd lambda bosses to downstream of the the main cats on the GM 3.2 down-pipes?

[laney101]

No performance issues before removing 3.2 cats (gm ones)

No i never reponsitioned sensors befote removing

Was the usual code for pre cat issue on v6 cant remeber numbernot been on for ages.  Checked via forum to know what ot was.

Installed none genuine cats  lights were still on so after a while decided to refit original cats bit i moved second sensor post main cat and upon refitting now have no eml for past 1000 miles or so

But while original cat were removed they were knocked about abot in garage and dont know if maybe insides dislodged or blocked

[Enceladus]

Piecing the clues together. Not necessarily in order.
Moving the original downstream lambdas downstream of the main cats switched off the EML fault light.
That suggests that one or both pre-cat (startup) cats might be faulty. But it could be another issue.

Replacing the the 3.2 down-pipes with 3.0 ones improved performance.
What did you do with the downstream lambdas? I assumed you installed extra ports for these in the down-pipes. Or were the pipes supplied with two lambda bosses?
Whatever, these pipes would only have had a main cat and no startup. So that also suggests something wrong with the pre-cats on the 3.2s
The pre-cats can get burnt out, they are intended to get to threshold temp as fast as possible. Also they can get choked with carbon if the engine is burning oil.

I seem to recall that at least one person on the forum was able to get a good idea of the condition of the surface of the honeycomb in the pre-cat using an endoscope. Perhaps bought in Lidl or Aldi? I can't recall was this through the upstream lambda port or maybe the pipe was on the bench.

A pair of new type approved catalytic down-pipes are likely to cost circa £320-£350. And do you need both or is it just just one side that's problematic, I'd want to be sure of success before shelling out.

Is there any reason you can't just re-install the 3.0L cats? They seemed to work whatever about type approval.

[Doctor Gollum]

The precats on the 3.2 don't like lots of idling or being driven gently, especially immediately after being caned

[laney101]

Cheers for replys guys

Yes 3.0 pipes had a boss welded in to run 2lambdas. So one before and one after the single cat

Why would i not put back on ?? Simple dont want engine light on dash all time its annoying and certain garages wont pass mot with light on jist easier not having it on at all.. which it isnt now usong original 3.2 downpipes.

However as you say light gone out due to moving post precat sensor so pote tially precars are nackered l.

Ive never had joy woth aftermarket cats on omegas however mever boight good type approved ones so pptentially buyomg good exspeanove ones would be good odea.

Tempted to refit 3.0 ones for now see if performance improves again if does its cats.. and hunt down a good set of brand new type approved cats..

Orrr if performance is restored with 3.0 cats fit a lambda spscer post cat sensor see if light goes out haha.

My 3.2 mainly does 2mile journey to work and back 5 days a week ... and beyond that it mostly town drivivng so fair bit of idling and light driving .. although every avalable chance it does get a good blast always has done but yes once caned may be idling for while at lights etc haha..

Hmm cheers again for help guys

[Doctor Gollum]

Two miles isn't enough...

It won't ever get up to temp, so will always be running with fuel enrichment, not only does this kill the fuel consumption, but you may as well pour petrol down the exhaust.

I would wager that if you drove it an extra 20 miles on each commute, the light would go off.

And you could move the bosses if you haven't already.

[biggriffin]

Two miles isn't enough...

It won't ever get up to temp, so will always be running with fuel enrichment, not only does this kill the fuel consumption, but you may as well pour petrol down the exhaust.

I would wager that if you drove it an extra 20 miles on each commute, the light would go off.

And you could move the bosses if you haven't already.

 ^^^^^ this,,,

You short run is killing the poor thing, it needs to stretch it's legs, as DG said a good 20 mile run,

[Enceladus]

So once again piecing together the clues you give us.

Original 3.2 cats - un-modded - EML on 6+ years
Aftermarket 3.0 cats - modded - 2nd lambda port welded in downstream of cat - EML on
Original 3.2 cats re-installed - un-modded - EML on
Original 3.2 cats - modded - 2nd lambda port moved to post cat - EML off & down on power

The issue with the above scenario is that the 3.0 cats still produced a fault code. The second lambdas were installed downstream of the single cat and it didn't clear the EML. So it might be the lambda sensors are worn out, it might be the starter pre-cats are blocked, it might be a wiring fault, it might be ..........

[laney101]

It does 2 miles to work 2 miles back.. but does longer journeys regulary does good runs of 30 to 40 miles up and down motorway gets good blasts on occassio  and is used to go on holidays in which are few hundred mile runs at a time..
It done that since 60odd thousand miles and been fine.

No light is on now since moving second sensor post main cat  so that is fine now.
Sensors were all replaced when welded new boses in so all four are new and have no light so probobly is a precat issue.

3.0 pipes were probobly cheap crap pattern cats not doing much.

On the 2 mile journey i let it warm up a bit before leaving for work... and when i arrive at work i leave it running for 5 to ten mins.. idle is always 550 ish (not cold idle)  so no fuel enrichment. And temp gauge rising.

Done ut fir years never had issues.. if it is that thats messed the original 17 ysar old.cats up... its fine ill just get cats sorted and be ok for another 17 years haha.

Thinking it precats are shot probobly slightly blocked or broken away inside. Causing back pressure build up slightly.... but as second sensor moved behind main cat lambdas are reading fine as main cat ok.

Im either gonna get good sports cats install in 3.0 sownpipes and refit them.

Orrr try and pruchase type approved 3.2 downpipes with new precats

Two miles isn't enough...

It won't ever get up to temp, so will always be running with fuel enrichment, not only does this kill the fuel consumption, but you may as well pour petrol down the exhaust.

I would wager that if you drove it an extra 20 miles on each commute, the light would go off.

And you could move the bosses if you haven't already.

 ^^^^^ this,,,

You short run is killing the poor thing, it needs to stretch it's legs, as DG said a good 20 mile run,