Stuttering & hestitation on boost

[Murf]

It only happens when youve been on a long run, if your driving for more than half an hour or so the car seems to stutter a couple of times, not boost as high as its set too and generally feels like its bogging down.
If you start the car from cold and drive it gently till it warms up it goes like shit off a shovel untill the half hour or so, then it starts to play up. If i turn off my ebc and run actuator pressure it runs fine, it only seems to be about 12 psi and above that the problem becomes apparent.

Has new dizzy cap and arm, iridium colder grade plugs plugs etc etc. Ive been running an intake air temp gauage on it and it sits at 20 deg celcius driving about and rises briefly to 30-35 under boost (drops back as soon as you let off the throttle)

Any ideas chaps and chapettes??

[Paul Woods]

are the HT leads new murf? sounds to me like the spark is dropping out under high boost.

[MegatronUK]

I had similar early teething troubles - turned out to be duff plugs (they foul up like a b!tch on the 3S!, especially with the 20% extra fuel at idle on our conversions) and plug leads not seating properly.

I agree with Paul's suggestion of the spark not holding up under boost.

What's the timing like, btw?

[Murf]

Havent checked the timing, no timing gun. I remember when i fitted the new plugs it missed a couple of times on high boost but i thought it was just fuel cut as i had fitted an EBC around that time which was crap and allowed boost spikes.
What plugs should i get if the £50 iridium ones aint up to the job! NGK copper ones like on my old mk2 turbo? a grade colder or just normal?

Plug leads have never been changed but should only have covered 30k.

[biteme]

Go for 1 or 2 grade colder NGK's. They're as good as anything else out there. Plug leads should be ok. Checked the dizzy cap and rotor arm?

[Murf]

Dizzy cap and arm are under 500 miles old, so are the plugs! Denso iridiums, one grade colder, cost me £50!!

[Paul Woods]

the favourites are the plugs but i wouldnt rule out the leads either,they are prone to drop sparks under load when faulty.

[Murf]

Well, new plugs are a tenner, new leads are £90!
Guess which i'll try first :)

[MegatronUK]

Yep, good old NGK copper - off the top of me noggin; BKR7E or BCPR7 are the part numbers you want. Cheap as chips too!

[Murf]

Yep, just looked on IMOC, bkr6e for standard, bkr7e for higher boost!
Cheers all, i'll pick some up tomorrow and see how they get on :)