Back to stock

So after perusing the aforementioned websites I started to realize that the setup of the engine created by the previous owner was somewhat risky. Specifically the 550 supra injectors and the NEO-AFC. The reason being because of the MR2's hybrid ignition control system. The MR2 uses a distributor to fire off each spark plug but the ECU can advance or retard the ignition timing also. A problem arises when piggyback style tuners are added into the equation. Piggyback tuners "trick" the ECU into doing what it wants. Because of this, situations can arise, if tuned without this knowledge, where the AFC tricks the ECU and into altering the timing and inadvertently causing detonation inside the cylinders which will break the ring lands off the pistons and then you are in a world of hurt because you engine needs to

                                                                                       be removed and opened up to repair.

The correct way to use an piggyback style tuner is quoted here from the 3S-GTE power primer. You need a wideband oxygen sensor and an adjustable fuel pressure regulator to use an SAFC. Then you lower the base fuel pressure with the regulator and add fuel small increments at a time with the AFC. This is a must read for anyone wanting to modify their MR2. It goes into detail about how to generate more power out of the MR2's 3sgte motor. It is written by a reputable and knowledgeable mr2 guru.

Some performance shops will tell you that you only need an S-AFC, but the safest combination is to use all three. Install both the fuel pressure regulator and the S-AFC. Set the S-AFC to zero adjustment across the board and adjust the base fuel pressure to 35psi (base fuel pressure is the pressure when the fuel pump is running but the engine is not, insert a paper clip in your diagnostic connector between +B and FP to produce this condition). Take the car to a dyno and hook a wideband O2 meter to it. Readjust the base fuel pressure to 30psi and add about 10% fuel at every point in the RPM range. Do a pull on the dyno and print out the AFR chart. It should start at around 14.5:1 and quickly drop to near 10.0:1 or even lower. Use the S-AFC to take out a little fuel in the ranges above 3500 RPMs where the AFR is under 11.5:1 but don't go under the stock (0%) level. When you (or the tuner) is finished, you should be at or close to 11.5:1 AFR...

Since I did not know how the previous owner had tuned the NEO-AFC and knowing that I did not have an adjustable fuel pressure regulator, I was anxious to get rid of the NEO-AFC. I bought secondhand OEM Toyota MR2 440cc/min injectors and sold off the supra 550cc/min injectors along with the AFC-NEO. I also, took out and sold the blitz electronic boost controller after seeing that the solenoid was not even connected. I bought a reliable EMSPowered.com Pro-Z manual boost controller to adjust the boost pressure levels. Here is a picture of the electronic boost controller solenoid when I found it. Notice the two black ports. They should each have a vacuum line attached. In the second picture you can see the electronic boost controller resting on the steering column between the speedometer and tachometer.

Along the lines of returning parts back to stock, I also got rid of the HKS blow off valve. Why? Basically Toyota got it right when they designed the stock bypass valve. Again quoting RickyB in the 3SGTE Power Primer;

An aftermarket Blow-off valve is not needed and will gain you nothing except maybe a loud sound and rough running or stalling after it goes off. The stock bypass valve is strong, fast and quiet.

It works perfectly well without creating an annoyingly high pitched screech noise. It is suitable throughout wide range of power levels. Another note is that the HKS valve vents blow off air to the atmosphere versus the stock bypass valve recirculating its bypass air back into the intake tract. Venting to the atmosphere is not how the gen2 3sgte engine was designed. The ECU manages the engine based on many parameters including the amount of measured air that comes into the engine. If an HKS valve is blowing off measured air to the atmosphere, the ECU does not have an accurate measurement of how much air is in the engine. This causes the engine to run rich for short amounts of time when the HKS valve blows off. This problem is cured recirculating the air back into the engine. HKS makes a fitting so that you can recirculate the air from the blow off valve but I decided that a nice, quiet, and reliable stock valve would be a better choice so I sold the HKS and replaced it with a stock valve(pictured below).