SMT8-FT Technical Manual
- FUEL TUNING
- LAMBDA TUNING
- ANALOG TUNING
- IGNITION TUNING
- FUEL MAP ENTRIES AND THEIR EFFECT
- AFR, POWER AND FUEL ECONOMY
The SMT8-FT can tune:
- The fuel injectors
- An Analog signal (or AFR signal)
- An Ignition (Crank) signal
Only one process or all of the above may be applicable to you!
This is the process of changing the amount of fuel your engine gets with the same amount of air. Some or most engines run a closed loop system: it measures the exhaust fumes and adjusts the fuel accordingly. Changing the fuel with the FT will not help in this instance: whatever fuel you put in extra, the stock ECU will take out again because it upsets the exhaust gas. However, and this is important, most closed loop systems stop operating at approximately 2500 RPM. You have to try it!
Most modern engines have a short and long term fuel control loop strategy. This may affect you in a couple of days. This can be found out with an OBD scanner. If you have problems with the fuel tuning you need to look at LAMBDA TUNING or ANALOG TUNING to supplement (or affect) the fuel tuning.
This is a process by which you change the Exhaust gas reading (Lambda) in order to ‘fool’ the stock ECU in to doing the right thing. There are two ways to look at it:
A) You put more fuel in by other means, and tune the Lambda signal down (leaner) to hide the fact that the ACTUAL mixture is rich.
B) You make the Lambda signal LEANER as it actual is, and the stock ECU puts more fuel in to compensate for it.
Of course, method B) can only adjust by a predefined (?) amount, so you may have to use both methods anyhow.
This is a process by which an analogue signal is ‘tampered’ with in order to prevent the stock ECU from knowing what you have done to the engine. Example: You have increased the manifold pressure and your AMP sensor tops out. Route the AMP sensor signal through the SMT8-FT and limit it! Example: You can get more fuel in to the engine when you ‘fool’ the MAF sensor. There are many more examples for analogue tuning. However, the SMT8-FT has only one analogue channel. More analogue channels can be found on different SMT8 products. See: Piggy-Back Products
Ignition tuning is only recommended on engines with no knock sensors, and only in absolute required circumstances. It is a little tricky to say the least, but otherwise very rewarding if you use good grade fuel. In this method you intercept the crank position sensor signal and play it back to the stock ECU a little later (retard) or a little early (advance). Most people ask: How is advance possible? It is a little complicated. The unit learns the ‘wheel pattern’ and the can ‘anticipate’ the next coming signal ahead of time.
When tuning with the LetRipp II a positive number adds and a negative number subtracts fuel as a percentage of the ECU injection length.
Example: Entry of 5, adds 5% fuel.
The Stock injection length can be displayed as well as the injector utilisation.
The AFR (Air Fuel Ratio) is one of the most important measurements in tuning fuel. The SMT8-FT can measure the signal from a NARROW BAND Lambda sensor and interpret it in AFR or Lambda.
AFR and Lambda are often used interchangeably. 1.00 Lambda = 14.7 AFR. Here are some important AFR numbers:
• 14.7 AFR = Normal Operation
• 13.2 – 13.8 AFR = Maximum Power
• 12.2 AFR = Maximum Power for Supercharged or Turbocharged Engines
• 15.5 AFR = Lean, point of Minimum Fuel Consumption
Modern engine technology can change the AFR numbers to a certain degree, but the principle remains: you can run the engine LEAN, but not on full power. Another way of looking at it – “if you want strong horses, you’ll need to feed them!"