EFI 101 Honda Tuning
To make an EFI system work, you need to have all the parts. Most of these are stock with your Honda.
* Fuel System
* Ignition system
* Map sensor/MAF sensor
* O2/Lambda Sensor
* Throttle Position Sensor
ECU - The brain of the electronic fuel injection system. The ECU gathers information from various sensorsabout what is happening. With this info gathered, the ECU will calculate output values to other sensors such as fuel duration, ignition timing, idel speed, and so forth.
Fuel System - Without fuel, the engine will never run. A Complete system includes the fuel tank/cell, pump, filter(s), injectors, pressure regulator, and lines to get it there.
Ignition system - Without a spark, the fuel won't combust and make power. From the distributor and all the parts in it such as the coil, ICM, Ignitor, and so forth,to the actual plugs and wires, a complete ignition system is an integral part of a complete EFI system.
MAP/MAF sensors - All Honda's to the best of my knowledge use a MAP, or Manifold Absolute Pressure sensor as opposed to the MAF, or Mass Air Flow sensor.
MAP detect pressure in the manifold and returns a voltage reading back to the ecu telling it how much air is coming in, what kind of vacuum/boost it is in, and how much load it is seeing. It's an amazing little thing. All the fuel and ignition maps are based off this one sensor's reading more than anything else. It tells the ecu what table to use. I will explain this in more detail later. For the sake of information, the MAF sensors act similarly, but instead of measuring pressure, they measure volume. The volume of air coming in is then translated to the ecu by voltage, just like the MAP.
O2/Lambda Sensor - The O2 sensor is used by the ECU to monitor the air/fuel ratio of the engine providing tighter control of engine emissions and improving fuel consumption. From a tuning point of view, it becomes an integral tool.
Throttle Position Sensor - Commonly called the TPS, the TPS transmits a voltage signal to the ECU in relation to throttle plate position. This tells the computer if the car is WOT, ideling, or somewhere in between. Many functions depend on the condition of WOT, so this is an important sensor in the EFI system The most important part of the system is the ecu. Ultimately, the ecu is what controls the car. It gives when needed, it takes when not needed. But the brain can only be as good as its "eyes" are- the sensors. If it 'sees' a wrong value, it's going to throw out a bad response. For this reason, among others, it is important to keep your ecu error-code free and all your sensors in proper working order.
The problem with boosting a honda is that from the factory, the computer is not designed with boost tables for fuel or ignition. After it sees about 2 or 3 psi of positive pressure, it will throw a code for the map sensor and send you into limp mode. The reason it has SOME positive boost pressure capabilty is that at 0 psi and 0 vacuum, depending on elevation it will go a little over at times. The 0 map will be suffice for 2 psi, so it allows it. But after that, it slams on the brakes to prevent you from damaging the motor and runs its limp mode program which will cut timing and a lot of your power.
When you turbo your honda you need some way to get around this.
There are 3 ways-
* Block it
* Trick it
* Alter it to read it
Blocking it is the cheap route, and also is the worst option. This method is used when you run an fmu and a missing-link system. The FMU provides the extra fuel by raising the rail pressure, needed to account for the extra air. The ecu's fuel map is not used other than it normally would be for all motor. Thus, you're relaying on exactly the FMU's, say, 12:1 raise in pressure for every psi of boost you throw at it. The missing link works with this, in that it blocks the ECU from ever seeing positive boost pressure. All it is is a check valve. It will let a certain extent go through, and vacuum is unchanged. But once it reaches positive pressure, it blocks the map sensor from reading anymore. The ecu never even knows that you boosted. This method is good for low power applications. 6psi on a larger turbo, 8-10 on a dinky turbo
Tricking it is a little more complex, but ultimately results in the same results. This method is accomplished when you use what's known as the VAFC Hack. Pioneered by Liam Slusser and found out by total accident, the hack is a mothod of tricking the map sensor into not reading boost. The stock honda map sensor is 1.8 bar for obd1 and 2 vehicles, and slightly less for obd0, giving the map the ability to READ up to 10.6 or 9.8 psi respectively. Now, remember, just because the MAP sensor can read it and convert it to a voltage does NOT mean that the Honda computer knows what the heck to do with it when it's out of its range. When running the hack, you use a set of large injectors, such as 440 or the popular DSM 450cc's. At idel, without control, these almost double the stock 240cc injectors would flood, stall, and wash out the cylinder walls of your motor. Using a VAFC, you can tune them down. Start at, say -40% at 1000 rpms and working your way up adding where fuel is needed. (This is an example only. be sure to tune your car on the dyno with a wideband o2.) The real trick comes in because of how the vafc is hooked up. It is wired to the map signal wire. When the vafc is tuned down low, it being a piggy back device, sends the altered readind to the computer. The computer thinks you are not in boost because it isn't reading it. This method is good for about 10psi. After that, not only are you approaching topping out the map sensor's reading range, you're about to throw a code on the ecu. The main disadvantge of this setup is that it does nothing to alter ignition timing. There's a LOT of power to be made or lost in ignition timing.