Perfect Power Online Manuals.


Support for your FT20 Unit.


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 : whatever you put in extra, the stock ECU will take out again. However, and this is important, most closed loop systems stop operating at approximately 2500 RPM.





When tuning with the LetRipp a positive number adds and a negative number subtracts fuel. A number of 100 means 1.00ms (milliseconds = 0.001 seconds) and is at idle - approx. 50% of your fuel injection. At full power it may be as little as 10% or less. Of course, the numbers change according to your engine. You can display the stock injection length and judge for yourself.





The AFR (Air Fuel Ratio) is one of the most important measurements in tuning fuel. Unfortunately, the Fuel Tuner has not been designed to measure it, but nonetheless an understanding of AFR is essential to choose an operating point which best suits its purpose:

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".





It is possible to tune without measuring the AFR, but it does require a bit more effort. From the start, running a "RICH" engine is safe - you will waste fuel, but you will not need to worry about damaging the engine. You should never run an engine at full  power lean, as this could damage the engine. It is best to try to lean the engine at cruising, however there will come a point where the engine "hunts", then you will need to make it richer again. Try reaching the ideal setting and keep it this way for a while.





Tuning your Fuel Tuner on the road as you drive is a very convenient way to establish the best settings for the best fuel economy. We suggest that you drive your vehicle (with the Fuel Tuner already installed on it ) for a period and record your driving style, using the "History" feature in the LetRipp Windows Tuning Software. The "History" feature shows where and how long you used the engine at its various operating points. You can then use this information to tune the spots where you have spent most of the time.





The Fuel Tune has two maps, called A and B. This feature allows you to have two different maps, with each map for different application or purpose. The map switching can be effected from three sources :


Hardware (via a physical switch)
Short the "MAPSW" input to GROUND = MAP B


Automatically (via the LetRipp Windows Tuning Software)
Enable the map switching (SYSTEM DEF) with either Air/Engine Temperature switch points (CONFIG : PARAMETER), for the Fuel Tuner to invoke Map "B" when either temperature is exceeded.


PC (Laptop) (using the LetRipp Windows Tuning Software)
The software can "force" a map (A or B), which allows the downloading and tuning of any item in them. During the "forced map" conditions the hardware and automatic map switching are disabled.





In order for this feature to operate, you will need to wire the SYNC input  (Purple Wire - Pin 7 of 10) to a suitable crank of RPM signal. You will also need to have the TPS input wired up (see OPTIONAL THROTTLE POSITION (TPS) INPUT above). This is because this feature has been designed to work only at WIDE OPEN THROTTLE.


When using this feature, you must understand that the RPM limit has its purpose, and extending it has a risk. You should only need to do it in very special circumstances or when absolutely necessary.


You will need to set two points in the LetRipp Windows Tuning Software ( under CONFIG, SYSTEM DEF) :

  • RPM from SYNC enable
  • Extended RPM enable

Once set, and you are on full throttle, then the FT will measure the ECU injection, and when it stops it will inject the last measured fuel plus any tuning you may have done until the stock ECU injects again, or you take the foot off the gas pedal. It is normal for engine manufacturers to run the ignition well beyond the RPM (fuel) limit.





The RPM limit of the Fuel Tuner is settable in the LetRipp Windows Tuning Software, under "Config" and then "Parameter Screen". The RPM limit is active BELOW the stock ECU limit, and when you have extended the RPM it is active as well (ABOVE the stock
ECU limit).