Tuning FAQ: 

Q:  How much of an effect will the additional mileage tricks have? 

All of the mileage tricks have proven beneficial.  Many of them should be done before the final tuning.  Tricks like increased tire pressures won’t have any affect on the tuning, but fuel tank vapors most certainly will.  You might be able to double your gains with added tricks. 

Q:  I’ve got all my settings where I’m happy with them.  I have fantastic mileage, but the car tends to stall at a stop.  Am I doing something wrong? 

There are instances where you can lean out the mixture at cruise for incredible mileage numbers, but the engine cannot sustain decent idle.  The fix (thanks to Mike Romero) is to take a TPS voltage reading.  Write this number down.  Next, remove the anti-tampering cap from the throttle stop screw.  Turn the screw to open the throttle to restore good idle.  Finally, loosen the TPS and rotate it back to restore stock voltage reading.  If you use the LM317 MAP adjust circuit, you might be able to lower the voltage reading with that, up to a point.  Too low of a TPS VREF will create other drivability issues.  Experimentation on your part will be your best guide. 

Q:  How much fuel economy increase is possible with the HAFC kit? 

Although we have some Installers getting 200%+ from the majority of their installs, Dutchman Enterprises is selling a 50% to 100% increase.  This means you don’t have to spend a week trying to tune for the absolute best possible results.  If you are able to deliver the promised increase, that is good enough.  You should be able to get better results with practice, but don’t kill yourself trying to extract every last mpg increase. 

Q:  I installed a switch in the CTS circuit, but still have horrid drivability issues when first started.  The engine can even be warmed up.  What gives? 

Chances are you are working with a vehicle that has a horrid ECU re-learn procedure.  Some vehicles will go through a process to re-establish certain parameters in the adaptive memory when the ECU Keep Alive Memory (KAM) is disrupted.  The simple fix is to flip the switch on the O2ptomizer from “Normal” to “IM Test Mode”.  This will provide constant voltage to the ECU and eliminate the re-learn procedure on every restart.  

Q:  I installed an HAFC with a 3X O2ptomizer and got 95% increase in mileage.  However, it is hard to start in the cooler weather.  What do I do? 

We have come up with a fix for the 3X O2ptomizers, but cannot implement it until the 4X program is underway.  In the mean time, you have 2 choices.  First and easiest is to simply cut the CTS wire coming out of the O2ptomizer.  Make sure you have enough wire on both sides of the cut to reconnect it again once the fix is implemented.  The other choice is to install a toggle switch on this wire.  Have the vehicle owner turn the switch off for the first couple of minutes until the engine warms up, then switch it on.  Neither option is ideal for mileage, but the switch option is better. 

Q:  I am only able to get about 204* reading on my CTS.  How do I increase it? 

If you have a 3X, you can’t.  You can lower the temp reading by adding resistance to the O2ptomizer’s CTS wire, but you can’t raise it above what you get with the O2ptomizer wired up with no additional resistance.  If you have a 4X version, you will be able to go in with the AMMO Box and raise that reading.  This also applies to the IAT circuit.

Q::  I have been playing with the adjustments for 2 months and haven’t gotten results.  What am I trying to accomplish? 

Wow!  This is quite a question.  For starters, there is a tuning manual you can download.  The early version suggests that there will be circuits on the 4X version that will not actually be included (we ran out of time and released the 4X without the extra features).  However, it does a good job of describing what the goals are and how to know when you have achieved them. 

Essentially, you have 3 goals: lower the lean limits, lean out the air/fuel mixture, and adjust ignition timing. 

The CTS and IAT circuits will lower your lean limits.  On most vehicles this will be sufficient.  On some vehicles, you will lean out the O2 circuit to the point where the computer will jump into Open Loop before you get to any drivability issues.  You need to lower your lean limits even further.  The LM317 adjustable voltage regulator circuit applied to either a MAP or TPS circuit will further lower your lean limits.  Just remember that this will advance your ignition timing. 

Leaning out the air/fuel mixture is the magic to achieving the fantastic mileage.  Keep in mind that too much is simply too much.  If you lean out the mixture to the point where the car stalls on take-off, shakes and shudders, and has no power, you are way too lean.  Richen up the mixture to restore drivability and retest. 

Ignition timing settings from the factory are often too far retarded for optimal power and economy.  This is done for nox emissions reasons.  Even after installing the HAFC kit, you may get better results from more timing advance (MAP offsets will lower lean limits while simultaneously advancing ignition timing).  On well-tuned engines, the timing requirements will be further retarded once the HAFC kit is installed.  If you can twist a distributor and retard/advance the timing, then that should be your first plan of attack.  If you have DIS or COP (or a system that doesn’t have adjustable timing), the IAT sensor will allow you to alter the timing by anywhere from 2 to as much as 10 degrees.  The hotter the air the computer sees, the further it retards the timing.  The cooler air will add advance.  Hotter air is more prone to detonation.