GC8 hesitation whilst cruising

[KwS]

Hi

V5 Type R, stock except axle back exhaust, BOV and simota panel filter.

Occasionally, when cruising along at say 50ks, 4th gear, very light throttle the engine will hesitate, almost like it bogs down. If i keep trying to cruise itll start to pop and crackle out the exhaust, itll lose power and start to slow down. Only way to keep it going is if i give it a little more gas, and then it comes back to life like nothing happened.

This morning i stopped at some lights just after it happened and noticed the idle was a bit higher than usual too (about 1100, normal is 750ish).

Its only happened a couple of times, but its bit of a bother and im concerned itll get worse.

Ive done some reading up and people are talking about a front O2 sensor causing similar issues? Any ideas on how to test this?

Apparently its had the AFM replaced semi-recently, but i wouldnt rule it out i guess.

Its not throwing any CEL, and tbh im not sure how to check codes on a V5 (only checked on legacies in the past), had a nosy and didnt see any green plugs staring back at me. Sadly it doesnt appear to be OBDII so my cable is useless.

Edit: oh and not sure if relevant, but some times when decelerating i get some nice pops and crackles (or bangs) from the exhaust. Not sure if its running rich or something. Not complaining as its awesome, but might indicate another symptom.

[Guest]

If its V5 you just didnt look far enough for the plugs and it will be OBD2.

I had a genuine afm die in a few months too but never threw a code. Idle tends to be afm related if it slowly develops and gradually gets worse.

[B4 2000]

coilpack?

check BOV is functioning properly?

and yes V5 should be OBDII

[KwS]

There no "normal" ODBII connection under the dash, only has something similar to this,

Its a blitz bov, vent to atmo but doesnt cause any idling issues. Other than the times as mentioned above the car is running very well.

[Guest]

Thats not where you find the OBD2 plug I think its down on the right off the steering wheel low down...?

[KwS]

That's not my photo only an example. I found my plug, which is grey, just above the foot vent in drivers foot well on lh side against trans tunnel.

[BD5_RS]

Let us know how you get on with the ODBII reading, you've pretty much described an occurrence I have with my V5. No codes, but 50-60k in 3rd or 4th at constant speed with very little throttle it'll die for a second. Does it maybe once every 10km.

My ideas were mainly sensor related, from my research Subarus do seem to have relatively shit quality sensors:

TPS (perhaps randomly showing throttle closed so it cuts fuel? Only seems to happen at very light throttle settings)

CTS (randomly giving 'cold' signal so it goes way rich. Internet suggest CTS common to go out of spec)

Oxy sensor fluctuations (I do have minor exhaust leak between turbo and DP - some random popping from exhaust)

AFM (Common fault as everyone knows - they probably replaced your one trying to fix that issue?)

[KwS]

Just as a follow up, found my OBDII connector, was right in front of my face >_<

Connected my cable (generic VAG OBDII cable from Dealextreme), fired up laptop, open EcuExplorer, told it to use Com1 as the port and BAM, found my ECU and connected.

Had historic trouble codes logged, but nothing current. Reset ECU and took it for a drive, whilst data logging. God damn i love technology, data logging is awesome!

Found that at idle O2 sensor fluctuates around 0.2V (0.20-0.30V) but thats about it. No matter what i do the sensor did not read above 0.35V, but did do large patches of reading the same value, and even went so far as to read 0-0.10V for huge periods of time. At WOT i got 0.25V.

No trouble codes logged after the run.

Looks like the O2 sensor has done its dash. But on the flip side, as i dont have a boost gauge, found im hitting 14-16PSI.

Since resetting the ECU the car actually feels like its running better. Could just be a placebo though.

[BD5_RS]

I pulled the downpipe off mine and cleaned up the gasket surfaces, before jamming some gasket goo (didn't actually have any proper exhaust stuff so used some hi temp rtv sealant :-\) on and reassembling.

200kms later I haven't had any further problems. I'm guessing an air leak at low exhaust flow right by the 02 sensor would cause odd readings, perhaps continually showing lean until ecu dumps enough fuel in to flood it?

It may be worth a shot checking the turbo to down pipe connection for leaks before replacing the sensor, although your readings do seem a bit odd.

[WRXONP]

you recheck o2 readings? should bounce between 0.2 - 0.8 constantly when hot

[ben-jamminn]

dragging up an old thread but did you ever find a fix? was it your 02 sensor?