OakleighParkScoobie

Am i right in saying there are 2 O2 sensors on my bugeye, one in the downpipe and one in the centre? I have changed the on in my centre pipe as it was giving dodgy readings on the dealers comp, but i have read threads about changing the lambda sensor on the down pipe to resolve a problem with low revs hesitation! Can anyone help?!!

Midlife......

iTrader: (2)

Correct for the bugeye WRX

The front sensor is the pseudo wideband lambda sensor that the ECU uses when on open loop to sort out fuelling at low speeds. If this sensor starts to fail then there may be problems with low speed hesitation as the ECU struggles to cope with the fuelling to get a stoich reading brom the failing Lambda sensor.

At higher speeds the ECU goes closed loop and reads from it's internal maps so driving is usually unaffected.

The rear 02 sensor is part of the emmisions control system. if this sensor fails it usually throws a CEL (P0420 usually) but there is no effect on engine performance !!

HTH

Midlife.....

OakleighParkScoobie

Thanx , I'll get another sensor then as its driving me nuts when the car hesitates, specially at the lights when some chav in his saxo is giving it large lol

funkyspider

So when you decat the downpipe - or prodrive cat one like I've just had fitted, the downpipe lambda goes ?

Is loosing that sensor what causes the P0420 - Catalyst System Efficiency Below Threshold. If so what does the ECU use when on Open Loop now.

Midlife......

iTrader: (2)

Funkyspider

To my mind the Bugeye WRX "downpipe" is the two sections containing two cats and the lambda sensor .

The section nearest the turbo is a straight round pipe housing the second cat (the first being in the up-pipe) and the next section (which has a flattened cat) houses the Lambda sensor.

With the bugeye It's possible to replace the first downpipe section with a simple pipe and keep the third cat and Lambda or simply buy a longer de-cat pipe replacing both cats.

Either way the "front" Lambda sensor remains in place

The ECU ignores anything to do with the 02 sensor behind the 3rd cat apart from throwing a CEL

I think I need help from a diagram......someone (rusty) posted one on cumbrianscoobs

Shaun

funkyspider

Ahhhh.. I was assuming the downpipe was just the shorter section I replaced. I l know exactly what you mean now.

Downpipe
Stainless exhausts manifolds headers

Cat pipe - with sensor
Stainless exhausts manifolds headers

or you can get a longer downpipe with both the above sections in one - this is classic, but I've seen newage ones too (HKS)
Stainless exhausts manifolds headers

Midlife......

iTrader: (2)

Funky

Nice Pictures

Much better than me trying to describe things

Cheers

Shaun

PS I'll have a look for my Bugeye decat pipe replacing both cats, it should be on the RCMS website

Midlife......

iTrader: (2)

Looked at RCMS website.....saw the price of £234 for the downpipe and remembered how much I'd spent !!

Shaun

OakleighParkScoobie

One other ? Would a dodgy lambda cause my car to idle lower than normal when hot?