Non-Toyota: Subaru WRX Issues

[JustCallMeOrlando]

Hey all,

I know this is non-Toyota, but there are a bunch of knowledgeable people on here, so I figure I'd ask here.

Wife's car is a 2000 model MY99 WRX, last of the original shape. It had been intermittently putting on the Check Engine Light (CEL), I checked the codes. Only code present was the heater circuit for the O2 sensor. Said to the missus, if your fuel economy gets worse, or it starts driving funny, let me know. It didn't, so I'd periodically check it.

Time went past, had the timing belt replaced, he complained it wasn't making boost. Little diagnosis, it was, it just felt crappy doing it. I drove it around for a bit and occasionally it'd stumble really bad. Pulled the codes, knock sensor. Yep, that'd explain it.

Just to make sure, I tried to reset the ECU to clear the codes. Every time I tried, it would complain about the oxygen sensor and refused to reset.

Fair enough, universal O2 sensor ordered, and new knock sensor from Subaru. O2 sensor I was told was a 4-wire. When I got it off, it was a bloody 3-wire. Everything was apart, so I just installed and gave the signal ground a nice earth. Installed the knock sensor at the same position as the previous one, reset ECU, car no longer throws codes. Fuel economy wise I'm not sure, it used about the same as the previous tank, but I've been giving it a bit of welly, so given it's a turbo that can mess with the fuel economy. Doesn't seem too far from normal though.

The driving experience is somewhat different though. While not stuttering in the same way, and generally feeling a bit more spirited, it's still not right. Feels decent at half throttle, feels fine at cruise. At partial throttle, particularly when cold, the car can be quite jerky. At WOT, it feels flat, and almost like it's missing up top, right when it's coming on strong. Spark plugs have probably about 30000km on them, but I'd need to check the logbook for when I did them, they're Iridiums. Fuel treatment and new fuel filter added recently when originally diagnosing it.

Any ideas what could cause this? For the price, I'm almost tempted to just get another 3-wire sensor just to rule it out. I may change the plugs too just so I can rule that out. Car has about 220000km on it, so who knows, yet another thing could be failing (yay! ) MAF sensor was replaced about 20-30000km ago too. If that's crapped itself again (and it didn't throw a code either), I'll be suitably unimpressed.

Cheers,
Nathan

[charliechalk]

You've probably already checked, but vacuum leak or similar maybe? as for the flat top end, clutch slip maybe? going for simple things first

[YLD-16L]

It's common knowledge with Subarus that you only ever replace the O2 sensors with genuine Subaru replacements designed for your VIN, as stupid as it may sound even running different ones from the same chassis code can give you grief - retarded, yes.


As you already know the air flow meter sensors on your model can often being playing up and NOT throw a code either. I've seen them die at sub 20,000km too so don't rule that out.

I'd run a wide band on it ASAP as it sounds very much like you could be running lean under a few situations.

PS. Sell it and buy an evo

[JustCallMeOrlando]

Haven't checked much for vacuum leaks yet. Just a quick cursory glance. I would've picked it as idling worse if it did though.

Clutch slip is a possibility, not one I'm keen on doing

[JustCallMeOrlando]

It's common knowledge with Subarus that you only ever replace the O2 sensors with genuine Subaru replacements designed for your VIN, as stupid as it may sound even running different ones from the same chassis code can give you grief - retarded, yes.

It is? Yay, $320 here I come.

As you already know the air flow meter sensors on your model can often being playing up and NOT throw a code either. I've seen them die at sub 20,000km too so don't rule that out.

I'll give it a clean and then check it out. I'm sick of spending money on this damn thing, it's got the same amount of km's as my car, only aside from needing an aircon regas and a set of new starter contacts my car is eleventy billion times more reliable, oh wait, it's a Toyota.

I'd run a wide band on it ASAP as it sounds very much like you could be running lean under a few situations.

Good excuse to purchase my wideband then I suppose

PS. Sell it and buy an evo

She's about due for a new car, this one is fully paid off. Perhaps it's time for the talk. Only problem is getting rid of it will be difficult with it as is.

[YLD-16L]

Clutch test is easy, 4th gear rolling start and then WOT. You'll know straight away if it's slipping, but if it's that bad it'd be pretty doughy on enthusiastic gear changes too.


I think that Subaru have the worst diagnositc fault finding of any modern, it fails to pick up many faults.

[mattysshop]

it sounds very similar to the AFM issue my mate was having with his GT forester..

[RobST162]

yeah my mum's suby has the same issue Gen 3 RX Liberty

i might try cleaning that sensor.... wherever it is

[StuC]

silly q - the timing belt isnt a tooth out or anything?

[JustCallMeOrlando]

StuC, the thought had crossed my mind. There is definitely something wrong with it since coming back from having the timing belt done, but I wasn't driving it enough before to tell. It was my initial diagnosis before the knock sensor code was found.

On a side note, I got some contact cleaner for the MAF sensor. I have a new air filter because it was well overdue, and I have a set of new spark plugs. Seems I changed them about 50000km ago. NGK claims 60000 miles for them in an NA engine. Given it's a turbo and had a hard life recently (probably running in some sort of limp home mode for a while), for $80 it's worth changing them.

[jzk25]

MAF faults are a recurring problem with this model. The reason it doesn't set a code is because it is still giving out a reasonable value, it's just the wrong one. Three usual symptoms of MAF fault are hunting at idle, what you are describing and the MAF flat lining at 3.5v and the engine dying at ~4000rpm.

Plugs are 50000km intervals but can die prematurely as 1.1mm gap is specified from factory where it should really be .8mm. Iridiums and Suabrus don't mix, use PFR6G's.

Check the boost level. If they overboost it feels like surging as they don;t have the 'head through the windscreen' boost cut that other models do.

The engine management on subarus is actually super fussy, way moreso than toyota. The MY99/00 setup is just not very good. MY01 on is all Denso and way better. Prior to 01 is all JECS so has Nissan Aids.

[RobST162]

Orlando let us know how that goes!

[StuC]

It could be throwing knock sensor codes if its pinging/knocking its arse off due to timing being out though - that sounds plausible doesnt it??
Im not actually familiar with Sub diag software so not sure it operates. Give me Benzes and toyotas

[JustCallMeOrlando]

MAF faults are a recurring problem with this model. The reason it doesn't set a code is because it is still giving out a reasonable value, it's just the wrong one. Three usual symptoms of MAF fault are hunting at idle, what you are describing and the MAF flat lining at 3.5v and the engine dying at ~4000rpm.

Idle is hit and miss, sometimes it's okay, when it first came back it was hunting a bit. Haven't checked the MAF voltage. Define engine dying? It feels f'ing flat, but it keeps revving.

Plugs are 50000km intervals but can die prematurely as 1.1mm gap is specified from factory where it should really be .8mm. Iridiums and Suabrus don't mix, use PFR6G's.

I only ended up with Iridium's because that's what I'd put in there previously, and when the car didn't have any problems, they worked perfectly.

Check the boost level. If they overboost it feels like surging as they don;t have the 'head through the windscreen' boost cut that other models do.

Doubt it's overboosting. If feels quite flat, and not pulling hard enough to be near boost cut. Aside from a catback 3" exhaust she's stock as a rock.

The engine management on subarus is actually super fussy, way moreso than toyota. The MY99/00 setup is just not very good. MY01 on is all Denso and way better. Prior to 01 is all JECS so has Nissan Aids.

Haha, gold

I shall let you all know what happens. I'll give it a couple of fuel tanks after cleaning and replacing stuff before committing to purchasing something like another MAF. That will give me an idea how the O2 sensor is working (if it's not chances are I'll get some pretty crap fuel economy).

[JustCallMeOrlando]

Well, still got the plugs to do, but new air filter in and cleaned the MAF. Dropped a heap of contact cleaner on the sensor over 3 goes. Drove the car, feels, well, sorted again. Stupid f'ing sensor, will give it another blast when I do the plugs. If it doesn't come good over time, I'll buy a new MAF, even if what I did didn't permanently sort it, it's in the right area.

Thanks for the help guys!