Non-Toyota: Subaru WRX hesitation

[JustCallMeOrlando]

Hey all,

Non Toyota, was wondering if anyone has any experience with Subaru WRX's? Steph's car has had what started out to be a bit of a miss when you're driving along a freeway. Got a little worse over time, and then things slowly got worse and worse. Now, it's got a hesitation when pootling along at lower speeds, I think I've narrowed it down to as it comes onto boost.

The first I changed was the fuel filter, because her uncle the previous owner couldn't remember when it was last done and the car has 180000km now. I next changed the plugs, because the platinums in there had been changed before the 100000km service. They looked fairly sad. Both of these things made me feel a little better, albeit poorer, but alas made no difference.

When it comes onto boost, the power just seems to flatten out to nothing, and it's rough as guts. I've had to replace the boost controller hosing as her uncle broke it, but it's made no difference. Wastegate doesn't appear to be sticking, although that really shouldn't affect it this way. I've driven it with the electronic components to the boost control removed, but it was still not smooth.

The ECU is producing no codes. I'm currently leaning towards it maybe being the ignition leads, but I have to remove a heap of stuff to check them, so I've not done it yet.

I was just wondering if anyone has some suggestions for what I could also check, and whether they think I've been going along down the right track. Also, if someone has experienced something similar with a WRX I'd love to know.

Cheers,
Nathan

[big_zop]

While not the same car, my wife's Rio had a major drop in power but i dont know how sudden it was. We did the same, checked the plugs and leads and looked for any broken hoses.

Turns out it actually was the leads, even though it ran the same (rough) when you unplugged each one, but the normal idle was fine.

As it only seems to be occuring when coming on boost, it shouldnt be a cracked pipe (not sure if they are MAF/MAP) - but if its MAP could it be associated with the sensor (and wouldnt that throw a code up?).

Got a boost gauge hooked up? Could the turbo be fubared?

[JustCallMeOrlando]

Nah. No boost gauge atm. Don't think the turbo is munted. it started happening under realy low loads on the freeway. Leads will be my first stop but they are such a slut to get off. removal of the overflow and half the intake!

[ed]

sounds like spark

[The Real Roadrunner]

if it was spark it would generally happen at the point of peak torque.

afm clean or is it covered in shite?
what year model?
fuel consumption good or bad? should get 400kms to a tank or better depending on engine condition.
any mods?
seen inlet pipes to the turbo cracking on my99 onwards, this induces lean spots and hesitations under light throttle.

need more info

cheers
linden

[oldcorollas]

i vote hesitation = lean...

hmm.. put a multimeter on the oxy sensor pin, and see if it drops quickly (ie, to less than 0.5V) when the hesitation happens..
bodgy, but will show if something major is wrong with AFR and is easy.

could also be that when in closed loop the O2 is rooted and giving wrong feedback.. so when you start to go out of CL (if ti doesn't immdeiately revert to table?) then it might be leaner than it expects and thinks?

hmm.. check O2... they are only mean tto last 50-120Kkm or something like that..

[Vios-GT_07]

i was told by a subaru specialist back in victoria..

the Boxer engine builds up a lot of carbon because of its design... that's why subaru's carbon cleaning products are really good.. and the shop actually recommended to do it every 40,00 kms, at the major service..

just something to try.. it's not too expensive a procedure and does have benefits even if it doesn't solve your problem , otherwise OC's suggestion about the o2 is also one of the more common faults with them

[JustCallMeOrlando]

if it was spark it would generally happen at the point of peak torque.

afm clean or is it covered in shite?
what year model?
fuel consumption good or bad? should get 400kms to a tank or better depending on engine condition.
any mods?
seen inlet pipes to the turbo cracking on my99 onwards, this induces lean spots and hesitations under light throttle.

Hmm, to be honest it probably began like that, now it seems to just die in the ass as soon as it comes onto boost, an initial surge followed by what feels like a flat line.

AFM cleaned and the wire cleaned with contact cleaner, the stuff you use for cleaning off delicate electronics.

2000 model MY99. Very last of the original shape.

Fuel consumption okay last time I checked, but it's not my car. She's not been complaining really about it. Returns over 400km easy, probably 500-550km, it does lots of freeway driving.

3" catback muffler was on it when she got it. That's it though.

Checked the inlet piping when I pulled the spark plugs, had to remove it all to get to them Same thing I'm going to have to do to check the leads

[JustCallMeOrlando]

hmm.. check O2... they are only mean tto last 50-120Kkm or something like that..

That's true. O2 is a definite possibility, it's previously thrown an O2 sensor code, but it's not thrown it in the 40-50000km since we last pulled the codes.

[ed]

if it was spark it would generally happen at the point of peak torque

yeah, then you leave it for a few months, and it starts to fail under load....

[Forcefed6]

I had a similar thing happen with my Subaru a few years back.... It started out as an intermittent miss under light acceleration. More with WOT tho.

Mine turned out to be leads. I only found this out when it got so bad on the highway one night (it would even miss at idle by this time), I pulled over to have a look. You definatly could see the stray sparks from the old leads.

This might not be your problem, but it sounds very similar.

As mentioned, the o2 sounds like a good thing to check too.

[Kedderz]

Check your AFM, use a working one $10 says its the AFM ;-)

[JustCallMeOrlando]

I had a similar thing happen with my Subaru a few years back.... It started out as an intermittent miss under light acceleration. More with WOT tho.

Mine turned out to be leads. I only found this out when it got so bad on the highway one night (it would even miss at idle by this time), I pulled over to have a look. You definatly could see the stray sparks from the old leads.

Perhaps I should open the bonnet at night.

[JustCallMeOrlando]

Check your AFM, use a working one $10 says its the AFM ;-)

What makes you so sure bud?

[Kedderz]

mate had the EXACT same problems and its highly common the AFM's crap out. He got it replaced under used car warranty, no problems since ;-)