Serious Misfire Above 3/4 Throttle...

[God666]

Hi all,

About a month ago, my FG XR6T started to give a hint of misfire at WOT which at the time I thought may have been an abberation and I did nothing about investigating it. Last week I drove Syd to Melb and back and not surprisingly, didn't use WOT on the freeway however, I now find that anything above 3/4 throttle, it runs like crap, bangs and appears to misfire and looking in the rear view mirror, leaves quite a cloud of black smoke. It is not an occasional thing, as soon as you hit the loud pedal and goes to boost, gets to what you could call near full boost and then starts to bang away etc at which time common sense dictates dropping the foot from the accelerator. It runs perfect if you push the car hard, it only turns to crap when you start to get up to full boost.

If it is a misfire, it is more than one cylinder that is doing it which makes me think it is not a spark plug or coil pack breaking down.

It is running just north of 300rwkw with injectors, HDI GT2 cooler and piping, Bigmouth CAI, 100 cell cat.

52000km on the clock, most mods done at about 15000 km. Original spark plugs (have not pulled them out to check them).

Had several tanks of fuel through the car of different brands so I have eliminated poor fuel.

Any thoughts or guidance on what to look for/investigate other than taking it directly to my tuner?

Cheers,

G

[Wenier]

From what you've said I would be picking spark plugs or coils. Although it is still low k's it does have that similar effect to a coil break down as its when your loading it up.

I would start with the spark plugs, and gap as it maybe out. If that doesn't sort it then the coils would be next step.

[TXR05]

Sounds like a boost leak. maybe a shot O2 ?

[nelsonian101]

Had the same thing happen to me.

Extra boost was blowing out spark.

New plugs.

Regapped to 0.8mm.

Runs fine.

[God666]

Yep, spark plugs had eroded away to the extent where the gap was getting near 1.8mm! I couldn't believe how badly eroded they were at that age. The plugs in my BA lasted at least twice as long however, having said that, it was not running near the power levels of this one. Can I boldly assume that as you run higher boost etc, your plug life diminishes?

Anyway, new plugs gapped to 0.85 and it runs fine again.

Not the most difficult spark plugs to get at but reaching for that rear one gives the leg muscles a good stretch.