Please help me understand a/f adjustments.
When increasing boost from say 10 psi to 15 psi, how do you go about adjusting your a/f ratio to compensate the added levels of air? Can the (stock or stand alone) ecu self adjust all by itself? I understand the limitations of the stock ecu and injectors/pump etc.. but does the PFC or others do this?

Another example to help understand my question.
When you modded FD guys are at the dyno and you take two or three runs and you are increasing boost after each run, do you have to program your a/f ratio before or during the run? Hows it work?
Thanks in advance! D

 

Fuel maps

Nope, that's why people like Steve Kan make the big bucks tuning.

PFC is limted to your fuel system as well. It can't supply more fuel than your fuel system can provide.

 

Say you're at a stoplight and a supercharged Ford Pinto pulls up next to you revving his engine. You're currently running a conservative 10psi. So you decide to turn up the boost to 16 psi (with all of the supporting mods of course) from inside the car. Do you have to mess with your PFC too? Or will your Aftermarket ECU switch maps automatically?

 

automatically, fuel maps are based on the MAP sensor (amongst other things) -so long as you're tuned for that level of boost and have the requisite supporting mods.

 

You get "tuned" to run the 16 PSI, but you have your boost controller turned down to run 10 until you need it. You don't need to reprogram to run the lower boost setting.

 

tdazmansFD I have the Peter Farrell piggyback computer. It has a **** in the glove box for setting 1, stock for emissions testing, 2, 12lbs for pump gas, and 3, for race gas, as much boost as the car will make, 17 or 18. Turn the **** & you change your ignition, fuel, and boost map.

Setting two and three involved having a tuner put the car on the dyno to work up the maps.

The Farrell computer came with three pre-set maps but getting the maps reworked for your specifc car is the way to go.

The PFS units are pretty cheap used and so long as you stick with the twins and don't use a midpipe, is tuneable and does all you need for a fast street car.

 

Another way to see how your car is running with high boost is to get a wide band Fuel/Air ratio guage and see it for yourself~~~ not the crapy Fuel/Air ratio guages.... get a real wide band... it maybe a little pricy but that is as accurate you will ever get.

 

Thanks everyone for all your wisdom! One more question (I promise)
What is the definition of "duty cycle"?

 

Duty cycle refers to the percentage that something (solenoid, injector, etc) operates. A 100% duty cycle indicates that a part is operating at full capacity.

 

So if you increased your fuel pressure would that mess with the duty cycle? Or is that something that the ecu controls. If it is ecu controlled only, would you increase fuel use just by increasing pressure.

 

If you increase fuel pressure, then your injectors will inject more fuel at the same duty cycle. The ecu doesn't know you've increased fuel pressure so, yes, you would be adding more fuel with the same fuel mapping by raising the pressure.

Conversely, you could run lower injector duty cycles and higher fuel pressure and achieve the same total amount of fuel injected. However, most fuel pumps start crapping out at higher pressures (higher boost levels).

 

Okay, now I understand. Thanks alot!


Dan

 

unless your running 2 different types of petrol correct?..say 16psi on 93 oct and for 20psi on a 50/50 mix of 93+c16 or just straight c16...you would need 2 maps wouldnt you

 

Yes, to fully see the benefit of doing so.