Anyone have a setup like this? I need to know if the stock S4 ecu will fire ignition up to 9k rpm's, as the MS running fuel only would be ideal seeing as how im going to have to swap things around for smog every two years and would like to leave all the smog crap more or less intact.

 

Yep I've done it--called a piggy back setup. There's a few tricks to share the stock sensors but it's really pretty easy. Read the megamanual about sharing sensors and I've even posted on this forum about what bias resistor values to use.

You'll need the following inputs (assuming your S4 turbo):

RPM (F-39 connector)
CLT (2I G/W)
TPS (2G G/R)
IAT (2L G)
MAP (a vacuum/boost source off your LIM)

Connect up the injector wires to MS (3F, 3H, 3C, 3E)

Let the stock ECU control the fuel pump relay and provide 5v for the TPS.

I'd run a WBO2 in a second EGO circuit for tuning then swap over to a NB for cruise trimming of EGO.

Decide if you want: EGT readings, EBC and BAC control from MS.

That's it.

 

I'm not sure you'll be ok to 9k rpms though... I know that without the MS controlling ignition, the stock system starts suffering from some ignition breakup at high rpms.

 

The stock S4 ECU has a rev limiter set to something between 7K and 8K, I forget exactly where.

 

yeah, I'm not sure what kind of rev limiter it is though... if it's just a fuel cut rev limiter, he should be fine, but if it cuts fuel and retards ignition (or worse, cuts ignition completely) then there could be a problem.

 

Thanks guys, it's an s4 NA. I have hit the rev limiter many times, it definatly cuts fuel as there is no backfire or anything when you hit it. I'm not sure if it does ignition at the same time but i hope not. I do know of one person, mazdaspeed7 if any of you remember him, who was running piggyback on the s5 ecu and would run it up to 9.5k, so S5 definatly works. As for breakup, im probably going to get a cdi box so that shouldnt be to bad, so long as it doesnt go retard, cut spark, or worse go off the lookup table or soemthign and go crazy i should be ok,..

 

I hope you plan on beefing up the engine internals to go that high on rpm. I don't think the stock engine will take much of that 9.5k.

 

aux bridgey, it's built for 9k.