Stuttering in 4th@WOT

[skiptownmcat]

I've been having loads of problems with stuttering at wot in 4th, every time it starts happening I have to install new plugs to make it go away. I have gone through 5 sets in 20k of driving and have used itv20's, 22's and ngk's and they all do it.
Everything will be ok for a couple of months and then the stuttering starts, there is nothing shown on the logs, fuel pressure is good, plugs are gapped @ 0.7mm (.028"). I have stretched the coil springs and it always comes back.
Any ideas anyone?

[Steve @ VersaTune]

It could be a bad COP. For grins, try tightening the gap to .025"

[skiptownmcat]

COP= coil pack?
The thing is, I get no dtc's. I have tried .6mm as well with no joy. I suppose the only thing to do would be to buy a new coilpack and just keep swapping them out till its ok?

[Steve @ VersaTune]

I think Ford IDS/ Mazda MMDS dealer diag tools can test them. You may want to try that. I'm not sure what a new Coil On Plug module costs.

[skiptownmcat]

Will I have to remove VT for them to check it?

[Steve @ VersaTune]

VT will not affect their diagnostic testing.

If you revert to stock, and the problem does not occur with the stock tune, they may have trouble finding the problem.

If you leave VT on, they may make a note about the presence of aftermarket tuning software in the service log.

[skiptownmcat]

VT will not affect their diagnostic testing.

If you revert to stock, and the problem does not occur with the stock tune, they may have trouble finding the problem.

If you leave VT on, they may make a note about the presence of aftermarket tuning software in the service log.

Meh, warranty was reached and breached some time ago!!
It's done it stock, with hypertech and now with VT. Always the same, only 4th gear and only when the engine is loaded @4k rpm and over.
I did a log today it's funny because you can see the rpm wavering along as it climbs but it never throws a cel.

[Steve @ VersaTune]

How is fuel pressure?

[skiptownmcat]

Same as always, ~1800 psi.
I know the stutter will go as soon as I change the plugs only to return ~5k later. It's defo ignition related, no KR, fp is fine, afr's are as commanded, 1st to 3rd pull hard, 4th pulls hard till 4k them starts hesitating, 5th occasionally does it, 6th is fine.
If it was genuine miss-fire it should throw a cel and I would see rich afr's which is what stumps everyone who I speak to about it. And if it was a bad coilpack it would stutter all the time (so I was told)

[laxplayermjd]

how many miles are on your car? excess carbon build up on the valves?

I didnt believe this myself but i fixed a 335i with that just last week, it had 80 miles and the carbon build up was not the worst ive seen. It misfired under load only, 80% and up throttle.

Just throwing that out there, of course this isnt no bmw