Anyone Seen Any Mpg Gains From Removing the Cat

[nokia_aid]

thinking about taking the cat off to try and get a bit more mpg, anyone else tried it and seen any gains

[Gilbertd]

No but I'm gutting mine to get a bit more power and make it sound nicer. If you're running on LPG who gives a toss about mpg?

[tomas]

I have removed catalytic on my bmw x5 4.4 because it callapse inside..
Can tell gain in mpg but x5 goes better.. x5 sounds same when working on idle...have in past golf mark 4 1.6 same thing catalytic callapse..when it was removed on idle or when you driving you have sharp noise from exhaust system .. a bit anoying sound
On x5 i dont feel that

[Noo Noo]

Please be aware that at MOT time if the vehicle had a CAT fitted at the factory and it doesn't now it will fail irrespective of what the emissions are.

[nokia_aid]

if i was to fit a gutted cat the mot man wouldnt know

[Noo Noo]

if i was to fit a gutted cat the mot man wouldnt know

Shhhhh

[Gilbertd]

and some MoT testers are of the opinion that as a cat isn't required for emissions testing when running LPG, then the removal of the cat would be considered part of the conversion.

[LPGC]

and some MoT testers are of the opinion that as a cat isn't required for emissions testing when running LPG, then the removal of the cat would be considered part of the conversion.

Without wishing to go OTT and make a big thing of it Suggesting MOT man apples a bit of mechanical common sense / free thinking in this context, not in other contexts mate?

Genuine point of interest and more to the point (I think I used to know the answer here), what is required regards cats at MOT time? Wasn't it something like vehicles made after a certain year should fail if they don't have a cat fitted at test time? Not that I'm against there removal or anything - point of cats is to keep emissions down, so if emissions pass without cats then that's fair enough imo....

There seem to be a few models of vehicle that (I've found) will pick fault if cat downstream probes don't register lower voltage (and voltage swings) in lambda than cat upstream probes - one that comes to mind was an X5 3L... On petrol the downstream probe read the usual slowly fluctuating about .3 volts with correct upstream lambda flick, on LPG the downstream probe read a lower voltage with correct upstream lambda flick and fuel trims, the petrol ECU was taking issue with the lower downstream voltage on LPG... Without the cat the problem might have gone away or got worse?

Simon

[Gilbertd]

I did say some. I know two MoT testers, one follows the letter that says that if a cat was fitted when the vehicle was new it should be there when tested or it is a fail, the other takes the view that if the cats are no longer required for the emissions test if presented running on LPG, then the removal can be considered as part of the conversion. Just a difference in interpretation and, bear in mind, it is only a visual check to see if they are there or not and not a test on anything as such. There's quite a few items in the test that are up to the discretion of the tester. When does corrosion on a brake pipe become excessive for instance, what one tester would fail another would advise.

You probably will get problems on cars fitted with downstream lambda sensors but as mine doesn't have them, it isn't important in my case. I have heard of the downstream sensors being replaced with a couple of resistors arranged as a potential divider to simulate an all fine signal to fool the ECU too. There's very little swing on downstream sensors anyway if the cat is doing it's job so a fixed voltage should keep things happy. It's the sort of thing the boy racer brigade pay a fortune for when they buy their de-catted exhausts, a couple of empty bulges so it looks like cats are there and a couple of resistors in a plastic box with a plug on it. Money for old rope......

[LPGC]

Agreed on all points - And another point on the downstream sensor issue.. AEB ECUs (closed loop mixer and even sequential) and some other ECUs have programmable lambda emulation built in.. But whether or not software allows access to the programmable emulation is a different matter lol..

Simon

[TNT]

My MOT guy, is of the opinion in my case seeing at the emissions test on LPG is an open loop test, no cat is required. It is needed to have any chance of passing on petrol.

The Cat isn't very effective with LPG anyway. I had to switch back to petrol to check mine was actually still working right.