hey all, my car (mods in sig) runs perfectly on 95 octane fuel (premixed) boosts cleanly throughout the rev range and feels strong, idles mint etc etc..

However when I put 98 octane or even 100 octane fuel in, the car wont boost past 5-6psi..it does this in every gear and is more prominent when changing down from 4th to 3rd bout 5000rpm. It runs normally in every other aspect of the tune, idle, cruize etc etc...

Timing is at 25 degree's and decreases accordingly as boost increases, fuel maps are perfect, but on the dyno using 98/100 octane it shows very lean afr's around 5-6 psi..

Once I flush out the 98/100 octane and put 95 back in the problems go away and the car runs perfectly again.

Could this be a timing issue?

 

Id reckon its running too rich.
have you checked afrs?

 

fuel maps are perfect on 95 octane, on the dyno pulls nicely throughout the rev range, no flat spots or cutting out. did 20 odd pulls each one perfect.

on the dyno using 98/100 octane it shows very lean afr's around 5-6 psi.. just at he point where it cuts out...it feels lean aswell...we tried taking fuel out, putting fuel in..doesnt change a thing.

Might add that it only does this once the motor is hot and done a few pulls...and only on 98/100 octane fuel.. as previously mentioned, put 95 back in
the tank and all is well again.

Would using a higher octane fuel cause things to become too rich? do higher octane fuels enable to you run leaner mixtures?

injectors
injector drivers
ECU
Fuel Delivery etc are all fine, ive checked them a million times, been through 2x ECU's and numerous sets of injectors...

only thing that fixes it is 95 octane...

Im thinking its maybe a timing issue, as previously prior to the most recent tune, the motor was running 15 degrees of timing and had no problems on 98/100 octane at all. Now that its running 25 degrees i have these issues.