Yeah, did a search already.

The setup: S5 TII shortblock with S5 NA rotors
S5 HT18 snail with stock wastegate setup but manifold has been ported to lessen boost creep
S4 TII ECU and knock box, new knock sensor
S4 boost sensor
S5 coils
S4 TPS
S5 CAS
S5 AFM
S5 injectors
Single wire O2 sensor
2.5 inch exhaust all the way back (~10 feet) Dynomax muffler at the rear
NGK 7 leading/9 trailing plugs, new as are the plug wires.
Can't find a vacuum or intake leak anywhere.

Other than some mixing and matching everything's stock such as the FPR, it has the late pulsation damper. Using a MSD fuel pump. Fuel pressure is ~40 PSI at idle, don't know about acceleration, rules won't allow putting a fuel pressure gauge in cockpit without major $$ isolators etc. Boost is limited to ~7.5 PSI.

I run two filters: a big coarse element Fram before the fuel pump and after the pump a big fine element filter, about big as a fist. 93 octane with some 2 stroke mineral oil, ~1 oz/gallon and also running an S4 mechanical OMP.

Now that the engine is seated in a bit it runs great, with one exception: under boost/high load. Think 3rd gear WOT out of a medium speed corner, foot to the floor, boost coming up, doesn't happen under vacuum. It will intermittently jerk/stutter under these conditions, no backfires so I don't think its ignition related. Back off the throttle a bit, it smooths out. That sorta points toward fuel.

I'm concerned that it *might* be going lean and that won't do at all. But the plugs come out with sooty black negative electrodes and dark chocolate colored insulators.

Can't make it happen free rev, only under load and boost.

Weird.

Ideas?

 

Gonna go with detonation/lean as hell because of the hi comp rotors. Stock timing is also far to advanced for na rotors

 

Boost leak test.

 

Well, added a f/a ratio gauge and found that 1) the problem decreased considerably on its own 2) when it happened it goes full lean for a split second 3) the fuel pump (MSD) has decided to drop off pressure at times. So, some fixin' is in the works: 1) Walbro pump, 2) adding another inlet from the cell to the pump 3) going with larger fittings and line (#8 AN) at the pump.

Questions: I am considering 'fooling' the stock ECU into running a bit richer by adding a resistor to the coolant temp circuit. So this brings up the question of 1) what temp puts it into closed loop 2) based on my research it looks like a 100 ohm resistor would do the trick. Anybody done this?

 

have you tried using all 9's for plugs yet?

 

How about getting a good ecu to tune the car with since you're running 9.7:1 compression rotors. You are going to blow your motor running s5 na rotors on a stock ecu. A very good tune is absolutely required to reliably run high comp rotors on a turbo motor.

 

And please don't try to fool the ecu with a resistor. Just pay $450 to get your ecu modded to an rtek 2.1 at the least. NA rotors with a turbo is nothing to cheap out on.

 

0_o