New WRX Owner - Missfire when cold problem

[Xzist]

Hey guys!

 

I'm a new owner of a V1 WRX (K Reg import). I have owned the car about two weeks, everything seems pretty good. I have a Subaru Specialist just down the road from me but he's away on holiday for 4 weeks so i can't get him to have a look for me.

My problem is when i start my car from cold (the morning for example) i will let it run for 5 mins to warm up; (like I've been told to do) then I'm on my way. After 1/4 mile pretty much at the same point on the road each time on my journey to work it will start to missfire. I don't go taring off and never boost in the first couple of miles. When the missfire happens the engine won't rev i can shift down a gear but the revs still wont rise up and the car just wants to stop. If i pull over and stick it in neutral and let it idle for a bit then gently rev it it will suddenly burst back into life and then will be totally fine for the rest of the drive/day until it has cooled down again. It will do the same after work then on the way home. About a 1/4 of a mile in it will repeat the missfire etc. 

it never does it any other time only when its cold and within 1/4 mile from the origin. 

I have run the self diagnostics and it is coming up with faults on the Knock Sensor and the O2 sensor. 

Any ideas what i should try to fix this issue? 

Any help would be gratefully received.

If there is any info I that would help let me know and i can fill you in....

 

Cheers guys

 

 

[Xzist]

Didn't mention the engine check light doen't always come on. the fault codes are from the last time it had the problem and the light happened to come on this time. 90% of the time it will have the problem but no lights will show up.

 

[savage bulldogs]

Do the bonnet vents have the covers on the underneath ? . As my brv removed the cover under the drivers side vent . Rain used to drip onto the coil pack on cylinder #1 and cause a misfire when cold .

Or It could be plugs or the coilpacks themselves breaking down causing a misfire. As a misfire would give extra knock due to the piston not being forced down by the combustion . Also would throw up a o2 code due to the unburnt fuel passing the o2 sensor .

If it's not broke .....upgrade it 😊

[Xzist]

Thanks for the reply. It seems to do it everyday if it's raining or not. But i will check the vents to make sure. Would coil pack or plug make it miss fire when its cold only though?

If would have thought it would randomly do it the whole time.

I was a bit confused by the O2 sensor fault as i have a de cat exhaust and didn't think it had an O2 sensor. Is this correct?

It's almost like the choke is staying out too long and its not able to burn fuel and chocking out. Any way to test if the choke is on or not?

 

thanks 

[stants]

The o2 sensor is about 4" back from the hotside of the turbo.

If it's shagged you may just get the odd cel come up then go away same with the knock sensor. I'd start with the cheapest option of maybe looking at the condition of the plugs before changing anything more costly, www.importcarparts.co.uk is your best bet for genuine subaru sensors

Sent from my SM-G930F using Tapatalk

[Xzist]

Thanks for info. but would bad plugs cause a missfire only when cold but then be fine once its warmed up?

 

thanks

[Xzist]

Anyone else got any ideas?

[savage bulldogs]

It could be anything electronic as moisture would evaporate when warm and materials expand with heat (somtimes closing gaps in insulation)

Usual suspects for a misfire on a early classic are .

Coilpacks breaking down or the insulation getting brittle due to heat .

Spark plug condition.

Both of these can be visually checked before replacement and the plug that's blacker will normally be the cylinder that's missing . Check the plug gaps and for cracks in the porcelain. Check the coil pack plugs and insulation for cracks or arc'ing marks on the heads where the plugs are.

If it's not broke .....upgrade it 😊