Posted on

FUEL CONTROL

A speed density algorithm is used to calculate the fuel injection pulsewidth. The temperature used is called the “In Cylinder Temperature” which is calculated as being somewhere between the coolant temperature and the air temperature, depending on the air flowrate. However, this may not be perfect for the engine configuration when combined with the “warm up” and “start up” fuel multipliers, and thus the below adjustments are provided to fine tune the system at various temperatures. The speed density calculation does not apply when the engine is Cranking (speed below about 450 RPM). After combustion starts and the speed picks up above about 500 RPM, the engine begins the speed density calculation, along with the “Warm Up” and “Afterstart” fuel. Warm Up fuel is using a default table (more enrichment at colder engine) that can be tweaked here if needed – warm up fuel works at all operating conditions above cranking, but is 0 at a fully warm engine. Afterstart fuel enrichment has the special purpose of building the wall fuel films in manifold and cylinder is decreased with the number of revolutions as the film builds and the parts warm up rapidly – most of Afterstart fuel is gone within about 800 revolutions. The adjustments provided here can help fine tune it to the particular application.

Fuel -20F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 5F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 32F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 70F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 85F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 105F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 130F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Fuel 195F Cyl = This affects all of the fuel at this In-Cylinder temperature, except the cranking fuel.
Afterstart 20F = This affects the fuel at this Coolant Temperature, just after cranking, and lasts for just a few seconds.
Afterstart 65F = This affects the fuel at this Coolant Temperature, just after cranking, and lasts for just a few seconds.
Afterstart 170F = This affects the fuel at this Coolant Temperature, just after cranking, and lasts for just a few seconds.
Warmup 20F = This affects all of the fuel at this Coolant Temperature, except the cranking fuel.
Warmup 65F = This affects all of the fuel at this Coolant Temperature, except the cranking fuel.

6 comments on “FUEL CONTROL

  1. I have the #30062 dual T/B unit on a Mopar factory crossram, utilizing the FCC. I’m seeing a difference of +-40* between my Autometer mechanical temp gauge and the indicated temp on the display. When the engine is fully warmed up (driven 20-25 miles) the mechanical gauge reads 180* and the display reads 140+-. The thermostat is 180* and a digital temperature gun shows 180* at the thermostat housing. Both senders are in the top of the water pump housing; that is, they both share a common area to read from. I switched the locations and there is no difference in what they read. Is there a way to calibrate the hand-held to match the actual temperature? So far I’m very impressed with the FiTech unit. Great idle quality and very sharp acceleration. I’ve only put about 125 miles on it and am glad I made the switch from carburetors. I’m looking forward to you folks publishing a complete tuning guide. I’ve gotten a lot of info off the various web sites but it would be nice to have them in a manual.

    1. There should be no difference between the two, is there any codes in the system for a Coolant temp sensor? OG to main menu and look at Fault codes to see if there are. If you would like to test for a bad sensor than you can pick up another sensor from a local auto parts store, the easiest vehicle to get it from is a 95′ chevy 1500 pickup with a 5.7, when did you purchase the unit?

  2. fuel issue ! fitech efi 400 starts up fine but it is currently running way to rich i can smell the fuel not only when driving but from out side the car 5 ft away what adjustment can i make to better this ?

    also engine stalls at lights not sure if related issue but as you slow down to a stop it will hunt for a idle then once stoped stall starts right back up

    1. Check for fault codes in the system. If all is good adjust your throttle with the below steps.

      IAC Steps:

      Turn the driver’s side throttle adjustment screw IN (clockwise) half a turn to start with, with that done turn the key on and go to dashboard and find TPS and make sure it reads zero. If not, then shut the key off and wait for the numbers to go black then turn the key on again. Once that reads zero start the vehicle and find IAC Steps on dashboard. This number needs to be within 3-10 at warm idle. If the number reads zero then slowly turn the screw OUT (counter clockwise) until the IAC steps reads between 3-10. If the number is above 10 then shut the vehicle off and turn the screw IN as stated above and repeat the process until the IAC steps are between 3-10.

  3. Good Morning, just had EFI 400 put in my 71 chevelle. still in the first 100 miles and im getting slight dieseling affect when i shut down the car. also the garage fills with gas fumes after sitting for a while, but there isnt a noticeable gas leak or smell that i can find. almost smells like gas is permeating the fuel lines. are they poly or steal braided? also what should i do about the slight diesel affect?

    1. Lean out the target idle AFR. This can be found in Go EFI Tuning. Try 14.2.