Help Decat

[QDog]

Hi all

I have just fit a 3" Decat downpipe and non resonated centre section, now the car really feels like it's holding back when I accelerate, doesn't have any punch at all

It's a 2003 VRS, new NGK plugs, Simota Panel Filter, Newly recalled Coilpacks. What else do I check?

[sharkrider]

have you changed anything else? (I have a 3" de-cat, no issues..) I doubt the exhaust would be causing the issue.....

 

do you have a forge 007p that needs servicing?

[QDog]

No nothing else changed, got standard recirc on. No dash lights have come on either.

Could it be a maf issue?

[Mankee]

When you decat and/or fit a bigger downpipe, you should hear the turbo a lot more than with the standard cat in place. If it doesn't make a bloody racket, something isn't right! Lambda sensors fitted and plugged back in? Haven't accidentally snagged N75 wiring in the engine bay etc.?

[QDog]

Lambdas connected, no snagging in the engine bay, I do hear the turbo a bit more but I wouldn't say it's mega loud

[sharkrider]

mine sounds like its sucking the life out of the planet and spitting fire out the back! (it pops on high rev gear changes!)

[skidmoose]

What set up do you have sharkrider, as I am guna in the market for new exhaust soon and this sounds right up my street. Do you have to change the decat for mot? Or do you have a friendly mot man

[sharkrider]

I didn't do it, it was done by the previous owner... its a custom system basically, 3" stainless decat, sensors still in place, 3" stainless exhaust, resonator, and backbox (powerflow I think, its a powerflow twin tip) , its very meaty, yet quiet when cruising, pops on upchanges at high revs.... its a pretty awesome setup! it "looks" like there may be a cat in, but obviously there isn't, my tame mech noticed straight away ... but he didn't say whether it would be a problem MOT time...

 

the previous owner got it MOT'd with the decat in, but then the front suspension was knackered too when I bought it (I have changed all that) so I think he was a "mate"..

 

MOT time for me, I don't know.... I doubt it would pass immisions...  its got a map on, sai mapped out, don't know if any adjustments were made for the lack of a cat , but I never get any warning lights.

 

my exhaust tip is black sooty.... I have found a 3" stainless cat on ebay for about £60 , I could buy that and fit it if the worst comes to the worst.... we also have an Abarth and in the facebook owners club on there there is a guy who is happy to pass decat cars, but I don't know..... I would rather my tame mech does it, so I know all is well!

 

[Mankee]

If it's had the SAI mapped out, it's probably got the second lambda mapped out too. My engine management light came on 100-odd miles post-decat.

[sharkrider]

If it's had the SAI mapped out, it's probably got the second lambda mapped out too. My engine management light came on 100-odd miles post-decat.

it was mapped with the decat on, so I assume so..... I have done about 8k since I bought the car, and no warning lights.. need to whip out the sai pipes! lol... I have a blanking plate now

[Mankee]

I've got two SAI blanking plates. Neither on the engine that's actually in the car. Doh!

 

Back on topic, I'd be tempted to disconnect the exhaust after the decat and see if there is a restriction in the non-resonated centre section you've just fitted. Sounds like a long shot, but it's got to be related to a job that you've just completed.

[QDog]

Ok I have scanned it with my cheap generic eBay scanner and I get codes P0030 and P0135 which I am aware are Lambda, is it normal to get these codes after fitting a decat? Or could one of the sensors be no good?

I bought the exhaust second hand and was told by the owner it ran fine on his car

[sharkrider]

seems like it has picked up the missing cat and isn't happy.... lambda sensor is to do with the cat right? ... don't know what the fix is I'm afraid...

[QDog]

It's the pre cat lambda so I reckon that's faulty

[Mankee]

Yeah, that or the wiring. Might even be as silly as not being plugged back in properly! The post-cat lambda doesn't have an effect on the way the car runs. It's just an emissions checker.

[QDog]

Ok it's sorted

Turns out whoever fit the lambdas into the downpipe put them in the wrong way round, swapped them to match the original downpipe and bang I now have a proper running car, pulls like a train now.