Piggyback Heaven – How to tune your Super AFC Neo

First generation Super Air Fuel Controller

I get questions from readers about the AFC NEO, the legendary piggyback computer from Apexi that led the way for tuners since the mid 80s.

These questions vary from the advanced to the idiotic, but after getting a patch of comments asking questions about the unit and how it works, I’ve decided to go in depth and explain just what the AFC does.

The 2nd generation AFC.

To fully understand what the Super Air Flow Controller does, you must first understand what exactly you are trying to accomplish.

When adding a power adder such as a turbocharger, supercharger, upgrading your fuel system or upgrading your power adder can result in undesirable results without tuning your ECU.

When you add more fuel, or add more air, you need the ability to adjust fuel trims to reach the desired performance from your vehicle. To do this however, you will need a tuning computer, piggyback or standalone as well as understanding the 3 operating modes of the ECU itself.

A piggyback like the AFC is an easy, cheap alternative that allows you to get the job done with minimal hassle and cost. By splicing into your MAF or MAP sensor, the AFC gives you the ability to adjust the amount of air the sensor reads.

What does this change?  When you lower or raise the mass of air seen by the ECU,  you can lower and raise the IPW and subsequently the injector cycle.

By lowering the airflow value before it reaches the ECU, the ECU drops the IPW and basically compensates for the larger injectors or fuel pump you have installed.

While there are those members of the tuning community that likes to turn their nose up at such a crude and simplistic method of tuning. And while a piggyback isn’t IDEAL, it’s more than enough to get the job done, and I’ve tuned countless cars to the 400-500 hp range with nothing more than just a AFC for tuning.

But they do have a point… how you ask? We’ll get to that point later in the read.

Onward to your ECU’s modes, and explaining what each one does.

Limp Mode : This mode is when the ECU sees conditions that the manufacturer deemed “unsafe” and thus puts the car into this mode to prevent any serious damage. When one of these parameters is violated or breached, the ECU switches the car into limp mode, making the car overly rich and circumventing what could be certain disaster.

Limp Mode isn’t fun, but it will allow you to get the car home and / or to a mechanic for help.

The Super AFC II

Closed Loop : Closed Loop mode is where you as a tuner should spend the majority of your time. This loop describes the connection from the 02 sensor and your ECU / PCM. This mode helps the ECU determine if the previous combustion cycle was rich or lean, and what to do about it.

The ECU is aiming for stoichometric air fuel ratio, which would be 14.7:1, which is the ideal mixture for maximum fuel efficiency. Reaching this mixture will allow you to extract every last single bit of mileage from your vehicle.

As the ECU receives the narrowband voltage reading from your 02 sensor to determine the engine’s mixture, it sets values that we will speak about later.

These values are STFT ( Short Term Fuel Trim ) and LTFT ( Long Term Fuel Trim ) to adjust the fuel deliverability for the next combustion cycle. Whether or not your car is running lean or rich is an easy determination, once you have these fuel trim values.

Open Loop : Thirdly, but not lastly the final mode is what is commonly called “Open Loop” or Wide Open Throttle for those scoring at home. In this mode, the ECU reads values such as Intake Air Temperature ( IAT ), Barometric Pressure, and Manifold Absolute Pressure ( MAP ) to calculate the mixture required to operate the motor at WOT.

Based on the values the ECU reads from the motor, it calculates the amount of fuel needed to reach the desired AFR. While at WOT, the knock sensor informs the ECU when there’s more knock ( or pre-detonation ) than what it’s been programmed to accept. Using the feedback from the knock sensor, the ECU monitors the engine’s operation to ensure that things stay in one piece and don’t start melting.

The latest version of the AFC, the AFC NEO

In the event that the ECU sees an overly lean condition in the previous combustion cycle, it will then increase the value of the STFT, which in turn increases Injector Pulse Width ( IPW ) in an attempt to restore a stoich mixture.

In the event of an overly rich condition ( too much fuel ) the ECU will then lower the value of STFT, which in turn decreases the IPW to bring down the mixture back to the desired 14.7:1 / or .50 voltage via 02.

Now when the vehicle has run for an extended period of time, consistently rich or lean the PCM will turn the STFT value into the LTFT value, and return the STFT to zero. When tuning with a piggyback for maximum gas mileage, you want these 2 values as close to 0 as possible to prevent any modification to the Injector Pulse Width.

When tuning for maximum power however, ignition timing is the name of the game. If all other values such as IAT, boost and engine load are the same, your tuning changes to your AFC will dictate the ignition timing of your engine.

As the knock sensor is the ECU’s “eyes” at open loop operation, it’s important to monitor this value, because of the inherent nature of the SAFC.

Earlier, we spoke about possible downfalls of using a piggyback like the SAFC. Because you are “fooling” the ECU into thinking there is less air, there is more timing available right out of the box from the ECU.

Problem is, you haven’t truly changed the amount of air the engine is ingesting, you are merely fooling the ECU into giving you the IPW you need to get the car running. So when tuning your vehicle on a dyno at wide open throttle under load, you can see how this can become a problem.

So when you’ve upgraded your injectors to larger units, you need to remove more and more fuel ( or air flow reading to ECU in this case ). But since the injectors aren’t stock, despite the ECU treating them as such, the “factory IPW” creates additional fuel, that shouldn’t be there.

Additional fuel = rich condition = decreasing STFT until your car throws the good old P0170 CEL, Fuel Trim Malfunction (Bank 1).

So when tuning for maximum power, you must monitor knock to maintain maximum ignition advance in relation to your AFC.

When tuning for maximum gas mileage, you must monitor STFT, LTFT and the ACTUAL airflow value from your MAF or MAP. Please remember when monitoring your MAF or MAP, the reading given to you by a datalogger is the value AFTER the AFC has adjusted it.

To achieve true airflow value, you must take the value from your datalogger and divide it by the AFC Correction factor in decimal form.

For example, we have a Evolution XIII showing 19 lbs/min of airflow at 4500rpm, at 80% throttle you have adjusted the airflow reading by -21 on your AFC.

19lbs/min / 1-.021 = Actual Air flow.

Next up : WOT TUNING

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Piggyback Heaven – Installing a SAFC NEO in a SRT-4

Today we are installing the ever popular SAFC NEO into our Project SRT-4. While piggyback computers aren’t as commonplace today as they were 10 years ago, they are still quite useful for the tuner on a budget.

While I install quite a few AFC NEO’s, I don’t recommend this install for the SRT-4 due to the difference in TPS and MAP sensor voltage. The AFC NEO operates in a range from 0-5 volts, where as the SRT-4 does not.

When you add aftermarket injectors such as the 760cc ( or 76# for those domestic fellows ), you can cause all kinds of problems without a device to lean out the mixture. Using a SAFC, we aren’t truly “leaning out” or “turning down” the fuel, but rather fooling the ECU into seeing less air, thus accomplishing the same result.

OBDII vehicles such as our SRT-4 have 2 values you should keep your eyes on, the STFT ( short term fuel trim ) and LTFT ( long term fuel trim ). When the SRT-4’s ecu sees the overly rich condition created by the larger injectors and upgraded fuel system, it will decrease these values in a vain attempt to restore “normalcy”

The problem is, when the SRT-4’s STFT and LTFT reach a value of -14, the ECU throws the ever popular P0170 Check Engine Light, Fuel Trim Malfunction (Bank 1).

By installing our SAFC NEO, we can lower the airflow value before it reaches the ECU allowing us to adjust the injector pulse width and therefore leaning the vehicle out.

Tools you will need for this install :

  • Soldering iron
  • Solder
  • 10mm wrench
  • wire cutters

First you must undo the ECM, held to the chassis by 10mm bolts, then unplug the ECM terminals.

FIrst, locate your C1 connector, the fourth plug down on your ECM, it will have an BLACK housing.

Here is a look at front face of a ECM connector, the back of this connector is what you will need to pull off.

You will have to pull back on the mounting tabs ( all four ) and pull the back half of the housing off to expose the wires.

I really really really hate these connectors......

With the back half removed, we’ll start the wiring fun by starting with our ground wires. The two wires in question are brown and black, locate those on your AFC harness and find pin 18 on your C1 module.

Using your wire strippers, expose 2 spots of the wire approximately 2 inches apart. The brown wire needs to be soldered in before the black wire, and closer to the ECM.

With your grounds properly wired in and installed, we now move to the 2 power wires on the SAFC NEO. Locate pin 11 on ECM Connector C1, this pin is a blue wire with a red stripe.

Wire in your red wire and red with white stripe on the NEO harness to pin 11, in the same method as you did the ground wire. Make sure the red wire with white stripe is closest to the ECM.

Now with the power and ground sorted out, move onto the MAP signal wires on the NEO harness. These wires are white and yellow on the NEO harness, we will also be wiring the TPS wire ( gray NEO wire ) in at the same time.

Now locate pin 23 on orange ECM connector C2, pin 23 is a dark green / red wire. This wire should be cut, and the yellow NEO wire must be wired in leading TO the ECM.

The white wire is then wired into the opposite side, make sure to solder for best connection.

Now with the white wire connected to the vehicle’s MAP sensor, take your gray throttle position sensor wire ( gray ) and wire that inline with the white NEO wire. Make sure to wire the gray TPS signal closer inline to the actual MAP sensor found on the intake manifold.

Why wire the gray wire into the MAP sensor? because of the SRT-4’s 3-7 voltage range, the NEO’s normal operating range of 0-5 will cause issues when tuning fuel trims according to throttle position. Using the MAP sensor, we can tune for engine load, as opposed to guessing and hacking our way through different voltage ranges.

Here is an example of this wiring, please note the brown wire depicted is the actual gray TPS wire, and the light green / red wire is the NEO white wire. Sorry I had to extend the wires using another loom and didnt have colors available that were close to gray or white for that matter.

Now find your green RPM wire on the NEO harness, this should be wired into a tach adapter, msd part number 8913.

Connect to the gray Tach adapter wire for a consistent rpm reading based on the vehicle’s spark.

Now with your NEO fully wired up, make sure to pick up some loom and clean up your rat’s nest!!!

Now to setup your AFC NEO, go into the menu and select sensor type as “Pressure” as your SRT-4 operates on a MAP sensor.

Select the “in” value as 10, set the “out” value as 10 as well.

Go into the car setup, and change the cylinder value to 4 and set the “thr” setting to the arrow pointing up and right.

Now go into the “TH-POINT” Menu and set your throttle values to 20% for low settings and 80% for high throttle.

For example if your MAP sensor sees load under 20 percent, then it will use the low-settings on the AFC for adjustment. Anything higher than 80% will run off the high throttle map and anyhing inbetween the two maps the neo will interpolate between the 2.

Now run the NEO Harness inside the cabin, and you are all set!

Happy Boosting!

Case Studies – Project Supra hits the Dyno!

When we last left our 1997 Anniversary Edition Supra, it was just getting used to calling to it’s new owner and had been modded for the first time in its life.

Because the car is so new, my friend is adamant about going slow and keeping it BPU for a while. He even goes so far as to utter the sentence I have heard about a zillion times from customers over the years.

“No, I’m more than happy with this power level, I don’t need to mod the car any further”

When people usually say this to me, I snort in derision and just sit back as the mod bug proceeds to take a huge bite of their wallet.

My friend has been a employee of Apexi for over 7 years, and even he cannot deny the temptress that is the 2JZ.

Within a few days of installing the old school Super AFC, he went out and purchased an upgraded turbo, manifold, Greddy 4 row intercooler, a full set of Greddy gauges, and 660cc RC injectors.

The turbo installed is a T4 62-1 with a 4 inch inlet .70 a/r compressor, with a stage V 1.01 A/R exhaust side.

For a rough idea of how much of an upgrade this small turbo is, take a look at this side by side comparison of a T4 62-1 and a CT26.

He’s elected to go with a SSAutochrome style Ebay log style manifold coupled with a 44mm Tial wastegate dumping back into a 3inch downpipe and full exhaust with a high flow cat.

With just a few mods and a turbo / manifold swap, we head down to our friends at DSR, check them out here : http://www.dynospotracing.com/

Using the DatScan datalogger, we tap into the Supra’s ECM to get a firm readout on the engine’s vitals. More importantly we determine the tip-in point for boost as we dial in the fuel trims accordingly.

We are aiming for a 12.5 AFR at the transition and a rock solid 11:1 at WOT until redline. The Supra is running 22 psi of boost through a full catback and 3inch Vibrant High Flow Catalytic Converter.

After just an hour, the car put down a SAE corrected power level of 521 with 433 ft lbs of torque.

The Supra put down a very healthy number with an excellent fuel curve, all for just a handful of mods. Next up for the car is a bigger turbo, more boost and Crower cams!

Congratulations Eric!

Piggyback Heaven – Installing a SAFC in a MKIV Supra TT

I’ve died and gone to piggyback heaven in the early stages of 2012, as a good friend recently picked up a MINT 1997 Anniversary Edition Toyota Supra Turbo. I have always loved these cars and the insane amount of over-engineering that went into the legendary 2JZGTE.

Since this car is probably one of the ONLY stock Supras left on the face of planet Earth, my friend decides to go slow and just start at BPU for now. Basic Performance Upgrades for the Supra can routinely and reliably push the car into the mid 400 wheel horsepower range.

Here we install an older Apexi Super AFC piggyback fuel controller onto the Supra, just one part of the BPU process.

Things you will need
– S-AFC or AFC NEO – Depending on your preference. My buddy happens to be an ex-employee of Apexi, and he prefers the older AFCII. That’s what we’ll be installing in this writeup.
– 10mm socket
– Wire strippers
– soldering iron and solder
– flux if applicable

First disconnect the negative battery terminal, and open the passenger door to reveal the kickfloor and ECU panel.

Undo the three 10mm nuts and pull back on the ECU cover to reveal the ECU.

Next, take a look at the Supra ECU diagram, you will be splicing into most of the wires, and cutting just one.

Next locate the 40 pin plug, located closest to you if you are looking towards the front of the car. You are splicing the RED wire into pin 31 for switched power to the AFC unit, if you own the AFC NEO it will be the RED wire with WHITE stripe.

Next we locate the primary ECU plug that is part of the plastic shroud, again you want the plug closest to you or E10 for those who have a service manual. You will be splicing the green wire into the RPM signal pin 58

Here is a shot of the green wire spliced into pin 58.

Next we will ground the SAFC, make sure to locate your brown and black wires and FOLLOW the detailed instructions in your AFC manual. You must splice the black and brown wires apart on the ground pin, located on E11 pin 69.

Pin 69 must be spliced and soldered by placing the brown wire (ground 1) closest to the ECU, and the black wire (ground 2 ) an inch downstream of the ECU harness. Here is what you power and ground wires should look like installed.

Next keep the E11 plug in your hand and locate pin 43, which is the throttle position pin. Splice the gray wire into pin 43 for the throttle input to your AFC. Now, locate pin 66 and cut it leaving yourself plenty of room on either end of the wire.

Now take the yellow AFC wire and solder it into the wire you just cut, TOWARDS the ECU. After that take the white AFC wire and solder it into the wire, AWAY from the ECU

I used the Apexi supplied quick connectors on this Supra, as the plans are to move to a VPC or standalone later down the road. Soldering here is optional and not recommended should u have more plans for your 2JZ down the road.

Lastly, you can elect to wire the blue AFC wire to pin 48 on the E11 connector for narrowband 02 readings on the fly.

Now snap the ECU connectors back into the ECU and double check your wires for positive connection. Reconnect your battery cable and turn the ignition to the “on” position.

Once your AFC boots up, you can now make the proper adjustments before starting your Supra.

Select from the MAIN menu, go to SETTING, then to TH-POINT and set your LO value to 94, and then your HI value to 95% throttle.

Select from the MAIN menu, go to SENSOR TYPE and select HOT-WIRE with input values of 1 in and 1 out.

Select from the MAIN menu, go to CAR SELECT and select cylinder 6 with the throttle position in the upward position.

Now, use the NE-POINT menu in ETC to set your NE = 7000 RPM.

Since we are not installing injectors this time around, we will not be modifying the Supra’s low throttle fuel trims at this time.

Next up, installing the downpipe, exhaust and boost controller in the dash to 400 whp.