So this relates to a 3.8 DI motor. I'm one of the only ones running an e85 blend on my 991 TTS so there's not much help in the 991 forum.

Basically my 991 has been tuned running e30-e35 for the last year 3,000 miles. I have upgraded the turbos now and got misfires. Otherwise logs look great. But so weird that my plus are bad after only 4,000 miles. The only thing I can think of is that I ran an e85 blend.

Now my 997.2 (same 3.8 DI motor) has never seen e85 and my original plugs went for 40,000 miles before I changed them. Only gas used was pump 91 or MS109.

Curious if you guys running e85 on the 997.1's have any data.

Thx.

 

Running the extra ethanol content may want a smaller plug gap. If it is too big it could be blowing spark out causing the missfires.

We run E85 on my brothers 997.1TT and we run NGK Iridium 7's gapped at .024" (830rwhp on E85). When my car was making 1050rwhp on E85 I ran the NGK Iridium 8's gapped at .024"

I cannot recall what the gap is on factory plugs off the top of my head since it has been awhile.

 

Thx and sorry I should have clarified that I'm not running any ethanol now with the upgraded turbos. Ether pump 91 or MS109. I get misfires in both circumstances.

 

Wondering if it Could just be you need a colder plug under those circumstances.

 

May already have colder plugs in it, contrary to popular believe E85 likes colder plugs. If the 991 is anything like the 996 and 7, they don't enjoy marginally worn spark plugs, or coil packs, especially when the engine gets hot. . Maybe time for both?

 

Hey Adam. I think it's a combination of the added boost and maybe the plugs just being fouled. When you re-install gap a little tighter too.

 

My car with stock coils @ .025 gap would only make about 1000miles on E85 and 30+psi.

The proEFI coils seems to have resolved that. haven't done plugs in awhile! and more than 30psi

 

run a colder plug, tighten the gap to .024 as been suggested by few others, e85 does eat plugs quicker than pump or race fuel.

 

Thx Sam. Have you seen plugs go bad so quickly before on the 991? Seems strange to me but then i'm doing things a little different so not many data points on this.

Damn 30psi must be insane.

That's good to know. Sounds likely that ethanol was the culprit then. Thx.

 

Yeah I feel that's early either way so who knows. Testing can totally cause that though. On the 991 I have seen water kill em quick but otherwise no.

 

12k miles on my car since the E85 conversion (and new plugs). 24 psi max. Pump gas, E30, E85...never a misfire ever.

 

Mine had misfires to on e85 and I got rid of the iridium spark plug and went with denso pk20pr-p8 spark plug and your problem is solved.

 

Interesting. I have the Pk20PR's in my car.

 

That's a good plug. On the DI cars though it's different.