Hunting around a little near full throttle!

[rocketdog]

Around wide open throttle and fractionally before it hunts a little so you can feel a bit of a gentle pull pull pull as she accelerates a tiny bit and then backs off a little. Im thinking its hunting around the lamda sensor and it needs replacing or AFM needs a good clean. Any ideas from you Gurus? Its very rhythmical, around 2 oscillations a second.

 

[red reading]

Possible it is compressor surge from the turbo....does it do it if you turn the boost down abit?

 

[PobodY]

Any chance it's ignition related?

I had a problem at one stage with the plug gaps being too small. I didn't really notice it on the road, but on the dyno it was clearly building power then dying off as the spark blew-out... then picking up again as the spark got stronger.

Re-gapped the plugs to 0.8mm from 0.5mm (I think) and I could notice the difference when I drove it again.

 

[rocketdog]

Interesting points! I'll try them both out and see! How does the compressor surge work? I don't think the boost gauge fluctuates as it occurs but I could certainly reduce the boost slightly and see if that gives any clues! Does anybody know by the way what the symptoms of a faulty lamda show as?

 

[rocketdog]

I could set the AVCR to graph mode on boost and then check it after and see if the graph appears to go up and down on steady WOT!

 

[PobodY]

I don't think the ECU operates on closed-loop at WOT; it's only using the lambda sensor for partial throttle (so probably cruising speed).

 

[rocketdog]

Ok this problem is more perplexing because its intermittent, it went away for a few days then came back and now its gone again, however when I put the AVCR in graph mode for boost it does a nice little sinusoidal wave form so yes the boost is certainly fluctuating but cant still find a reason.

 

[rocketdog]

Have not tried checking plug gaps yep but that shouldn't be intermittent should it?