Fattony

iTrader: (1)

I want to get this cleared up, a buddy of mine who has an FD says if I modify I would have to get my FC mapped otherwise the engine will not compsate the excess from the modified parts, ie intake, exhaust, intercooler turbo, ect. Is it true the Rx stock ECU will not handle aftermarket part well, or is this a myth?

Thanks
Tony

slo

iTrader: (1)

Yes, the stock ECU can't handle anything more than a CAT back exhaust.

85rx-7gsl-se

iTrader: (2)

I am currently having problems with my JDM S4 TII engine. It has an open downpipe, cone filter intake, and a boost cut defencer. Maybe my stock TII ECU isn't going to cut it.

Aaron Cake

iTrader: (1)

There is a fundamental difference between the FD and FC EFI systems.

The FD system is a speed density system. It uses a MAP sensor to detect the amount of load on the engine, and then it goes to a fuel map and looks up an injector open time based on that MAP reading and RPM point, applies corrections like coolant and air temp, then opens the injectors for that time. If you increase airflow through the engine (open exhaust, bigger turbo, etc.) you will be flowing more air through the engine. However since the FD ECU judges load based on manifold pressure it will not know to inject more fuel (because the manifold pressure would not have changed) and thus the engine runs lean and you are picking apex seals out of your muffler...

The FC system is a mass air system. The ECU uses the AFM to measure the actual amount of air entering the engine, and then picks it's injector open time based on the amount of air and the RPM of the engine. It then applies correction values (coolant temp, air temp, O2, etc...) and opens the injector for that amount of time. More air through the engine opens the AFM more, so the ECU opens the injectors longer for more fuel. Thus you can do things like slap on a bigger exhaust, bolt on an upgraded turbo and the ECU will compensate...to a point. At some point you reach the limits of how far the ECU will drive the stock injectors (something like 80% duty cycle) and thus must upgrade...

If FDs had our EFI system, they wouldn't blow up nearly as often.

Fattony

iTrader: (1)

Thanks thats what I was looking for

Tony

TitosToy

ahhh...thanks for the explaintion aaron. now i can see how you could turbo your n/a and still use the stock ecu (at the time when you did) just as long as you dont push the duty cycle of the injectors, correct?

slo

iTrader: (1)

I never modified my car with a stock ECU, I went right for an E8.

But wouldn't a stock ECU be hitting boost cut with even a full exhaust, and with a boost cut defender doesn't it run real lean on top?