13 replies to this topic

[robt]

Last Thursday my missus bought a MY99 Foz GT. Well it has a few problems. It will run fine on light throttle but when I put it under load at about 2000rpm to 3000rpm it stutters and sometimes backfires. Over 3000rpm it runs fine with a WOT but its got real driveability issues in the lower rev range with a heavier throttle. I have already run a code check and it was clear. I have tried a new afm and it did nothing. I have checked all the vacuum hoses and they are all fine. The Y-pipe is ok too. I am thinking maybe the BOV is stuck as after the resonatorectomy it does not make a sound. Please if anyone can help I am at my wits end. I thought single turbos were easier to work on than twins. Oh and I have posted this on OZfoz too. Rob

[Dylan]

Might be coils?? Does it have the individual coil packs over the spark plugs?

[robt]

No it has the same setup as a GC8 so just leads. I am thinking O2 sensor. $86 from Bursons.

[robt]

Hey where does the knock sensor live on a Foz?

[Alex]

Hey where does the knock sensor live on a Foz?

raging guesses here.

dump pipe?
headers?

[RX25SE]

I think Dylan might be on the money Rob. From what you describe it sounds like an ignition breakdown. The O2 sensor is only used for fuel trimming and usually wont cause a driveability issue. If its faulty or out of range it will throw a code as it is an input. Similar story with the knock sensor. As the coils are an output, no code will be given. Knock sensors usually live on the block near the bottom of the cylinders. Also, if your looking at the running engine and suddenly go WOT can you hear a cracking (spark sound) near the coils, leads or plugs? Could also be the spark tracking down the outside of the plug to ground (crack in ceramic) or the 'tubes' (if it has them) at the end of the leads are not insulating properly allowing the spark to go to ground. Look for a small grey spot or pull them out with the engine running and you will see a spark jump to the head from the side of the faulty tube......but don't get zapped!!! I have a special tool for this.......an apprentice! Hope this helps. Cheers J

[Alex]

I think Dylan might be on the money Rob.
I have a special tool for this.......an apprentice!

bwwahaaaaahahahahahahahahhahahaa!!

you've made my day!!

[Ericmcg]

No it has the same setup as a GC8 so just leads.
I am thinking O2 sensor. $86 from Bursons.

Could be a bad lead or plug breaking down if its just happening under load, similar thing happened to a previous car of mine, ran ok when driving easy but when i hit the throttle hard then the bad plug lead used to cause a shudder and miss-fire.

[alexGT]

wrx knock sensors are usually located underneath the intake manifold next to the coolant cross over pipe. knock sensor should bring up a code if it was forked, stranger things have happened though. change/check the plugs first, they are cheaper to do than leads.

[robt]

Well I had a spare knock sensor and found a spot for it and it seems at least 50% better. I think its ignition. Plugs will be changed but completely rooted now. I need an apprentice.

[XXB4XX]

Before you start replacing the whole wiring system of the car, always check your BASICS, it could be as simple as fouled spark plugs, or a cracked plug (ceramics can crack)

[RX25SE]

or....grab a multimeter and check primary and secondary resistance in the coils. Primary 0.7-1.0 ohms (approx) Secondary 10-15k ohms (approx)

[Dylan]

wrx knock sensors are usually located underneath the intake manifold next to the coolant cross over pipe.

knock sensor should bring up a code if it was forked, stranger things have happened though.

change/check the plugs first, they are cheaper to do than leads.

I've read that it takes a LOT for a knock sensor to be deemed as 'faulty' by the ECU. It can still report false knocks and be classed as 'problem free' by the ECU.

Well I had a spare knock sensor and found a spot for it and it seems at least 50% better.
I think its ignition. Plugs will be changed but completely rooted now.
I need an apprentice.

My money is ignition breakdown.

So the GC8 of that era had individual coil packs on top of the spark plugs.

If that's the case, I'd recommend an upgrade to Bosch HEC716's (A lot of the RS Liberty boys have done this) rather than sourcing replacements through Subaru for these (expensive).

Should be able to get them through supercheap or repco. I am not sure if you can still buy them , they may have been replaced by a newer item but definitely worth the upgrade.

I did this upgrade on my engine a while ago, and I should have done it at day 1 as the improvement it made was amazing.



Could try this site if you are unsuccessful in tracking them down locally, Rob.

Dylan

No it has the same setup as a GC8 so just leads.

Just read this. Depending on what it actually is my previous post may be useless to your current situation but I will leave it there for future reference

(I'll be surprised if its different to my ignition set up)