k-jones-087

if you had a code p0420 cat effeciancy problem would it cause a boost problem in a bug wrx,as in,is it in limp home mode and stopping it from boosting??? got no where asking this on general tech page so hope experts can help.

deanb1980

i would of thought so have you tried removing the fault by removing the battery for about 2-3 hours and seeing if it comes back

k-jones-087

thanks for reply, ya have tried everything to fix this prob,its been ongoing for a long time and ive tried alot of the ovious things,this is only code so im thinking is it the cat messing things up,dont wanna get cat until i know this would cause loss of boost

deanb1980

a broken down cat will block the exhaust gases escaping causing the turbo not to boos properly had this on a customers evo every garage was saying it was a turbo but when we took it apart the cat had collapsed inside blocking the end so gasses couldnt escape causing it to go into limp mode

try and get a decat or see if someone has a cheap second hand cat

k-jones-087

cool, thats wat i was thinking,but wat was confusing me was car was passing emissions test so i was looking elsewhere, il try source another cat and see wat happens,thanks bud.

deanb1980

it could still pass emissions as when they check its on idle maybe when you put the boot down is where it struggles cause its blocked

i must say it could also be a lamba sensor these are expensive new but i would go for a second hand cat which will cost about £50 first as it would be the cheapest option to try

k-jones-087

emissions passed 2 on high idle,but barely, have replaced front lambda with denso replacement, exact same part number costing £100, the original is way more costly. so i presume its ok, now i think its not a lambda as such,its an air fuel sensor controlling mixture,and i think its a current sence type so cant be checked like normal lambda??

jura11

iTrader: (7)

Hi there

Those cheaper Denso are OK,but not so good as from dealer(those last longer than those from eBay for £90-£100),agree they're expensive from dealer,really depends

Its not proper AFR,still reads only as narrow band and is OK as you are said for controlling the air/fuel ratio

Jura

JDM_Stig

iTrader: (3)

You say that you have replaced the front 02, yet the code is for the downpipe.

k-jones-087

ya code is showing cat effeciency,which is main cat in downpipe,the reason i had changed front 02 sensor was because i had a code for it,which has now gone. the only thing i havent changed was the cat, because with this code i didnt think id loose so much boost, i just thought if cat wasnt great rear 02 would pick that up by switching more and tell ecu throwing on cel light, but i have very little boost,crap in fact, so im hoping cat is my only prob.

scoobyJim2

I had cell light come on once for front lambda sensor and car didn't limp.have you checked sensor after cat and if there is one in the downpipe/cat itself? I take it you have a scan tool/code reader? Try resetting ecu codes/dtc's unplugg one sensor,start car let cell light come on,read codes then reset ecu,reconnect plug,then unplugg next sensor and do the same thing untill you get the same or a simular code as p0420 cat efficency

scoobyJim2

^^

wrx271

iTrader: (1)

jura denso cover around 90% oe there is no way they are a cheap replacement far from it infact. in all fairness denso probably make oe for Subaru.

regards

dave

jonnyricer2

iTrader: (9)

Have you tried looking at live data to see when code first appeared in freeze frame data.

Had this on a yaris came up with cat effieciency but turned out yhe maf was dirty.

Maybe faulty maf sensor not reading enough air going into engine in turn messing up
the afr at certain points.in the rev range.

k-jones-087

ya, i actually have seen the same code in a few toyota yaris and cleaning the maf fixes them, but ive already replaced the maf, with again a denso replacement, if i bring the maf up on a graph on live data is does seem a bit lazy but does seem to be working, im gonna try a 2nd hand cat downpipe and see will that get rid of code and hopefully sort boost.