Fast 30400-KIT-EZ-EF Instructions Manual - page 51

51 

Accel Fuel is a fine-tuning detail to adjust how the engine responds to throttle changes. In general, it 

should only be adjusted after the ECU has had some time to learn and the engine is running well in 

steady-state operation - throttle not changing.  An exception to this is when the EZ-EFI

®

 system is 

installed on a port-injected application where fuel is supplied by injectors near each intake port instead 

of from an EZ-EFI

®

 throttle body.  These applications often require less Accel Fuel than a throttle 

body injection setup.  It may help to start out with Accel Fuel set to a negative value for port-injection 

applications.  

Tuning Accel Fuel is a subjective process. You may be able to feel that it’s not quite right, but it can 

sometimes be difficult to tell which way the adjustment needs to go. You may notice it when free-

revving the engine in neutral, pulling away from a stop or any time the throttle is opened quickly. The 

Accel Fuel adjustment applies to all of these situations. The best setting will be the one that works well 

for all of them. It is not necessarily the setting that makes one specific situation absolutely perfect, as 

that may require too much compromise in the others. 

If there is too much Accel Fuel, when the throttle is opened quickly the engine will sometimes feel as 

if it is struggling and/or generally not running cleanly. If there is too little Accel Fuel, you may notice a 

delay from when you open the throttle to when the engine responds.   

The Live Data screens may be useful in tuning Accel Fuel. Having somebody watch the live Air/Fuel 

Ratio (AFR) data (either the numeric display or the bar graph) while you drive and make quick throttle 

changes may reveal whether the engine is getting too much or too little Accel Fuel. When the throttle 

is opened quickly, there is a lot going on. AFR will often swing back and forth. You want to watch for 

an overall trend. 

As with most settings, it is good practice to make small, incremental changes and see what happens. If 

you make large changes to Accel Fuel, it is possible that you can go from too little to too much fuel 

without realizing you’ve passed right over the setting that makes the engine the happiest.   

The Accel Fuel setting can also be used as a troubleshooting tool for a specific type of installation 

problem. If the EZ-EFI

®

 system does not have a good ground connection to the battery, it is possible 

for the various sensor readings to appear jumpy to the ECU. (This jumpiness in the sensor readings 

may or may not show up on the hand-held’s Live Display screens.) This can fool the ECU into 

repeatedly invoking the Accel Fuel feature, causing extra fuel to be injected. This could lead to an 

overly rich and unstable idle and prevent the ECU from learning. Once the engine is fully warmed up, 

if temporarily turning the Accel Fuel setting all the way down makes the engine idle noticeably better 

(or conversely, if turning it all the way up makes it idle worse), that could indicate a bad ground or 

some other source of noise. After the test, remember to set the Accel Fuel setting back to its previous 

value.    

SETTING 

EFFECT 

Positive 

More Accel Fuel 

Negative 

Less Accel Fuel 

Cranking Fuel 

The ECU is programmed to inject extra fuel during cranking.  Most engines should be able to crank 

and start with the pre-programmed amount of cranking fuel.  However, if the engine seems to want