Recently (last 3 or 4 weeks) my 951 has started stuttering under WOT above 3.5K. I have run 16 psi for a year or so with great AFR and no problems. Now if I turn boost down to 12 psi or lower it pulls hard and had perfect afr, however at 14-15 psi or higher it stutters through the rpm band past 3.5k and AFR are a little jumpy 11-13. I have used no name injectors (43 lbs) and I was thinking those may be the culprit. Changed the bosch copper plugs and put in NGK BPR7es( one colder heat range than stock) and all plugs looked the same with no fouling and a decent looking tan colored isolator. They all had a small amount of gray ash deposits on the arm and a little oil on the threads (I think my turbo puts a little oil in the intake). The new plugs made no change.

Cap, rotor and coil are 1 year and 16K miles old. Wires are beru and they are red (not stock) but I have no record of when they were changed, the car has 100K on the clock. I pressure tested from the inlet of the intercooler foward and no leaks, but I am going to test from in front of the turbo next. Vac is 16-17 inches when warm. New HV fuel pump and filter. What are your thoughts on this problem?

 

the first things I would check that you haven't done yet are


swap known good injectors
check injector wiring at the clips

 

The problem is these are a weird flow (43lbs) and I dont know anyone locally with them. I'll check the wire at the clips though.

 

if you can find some injectors from a ford (36# brown tops) they will work I have been using them in mine for over a year now. you will just need to fatten it up with pressure or your fuel controller.

 

I'd bet money (yours), that your plug wires need replacing.