Compensation for A/F ratio

l0st-s0ul SG

when installing an after market performance high flowing air filter, no doubt there would be an increase in air flow to the engine.

my question is would the ECU compenstate the xtra increased air with xtra fuel or would an fuel pressure regulator be needed?

and also what is the difference when someone uses a piggy back ECU to change the mappings of the A/F ratio and someone who installs an fuel pressure regulartor?

AE86tofu SG

for the air filter dun need 2 worry one la....many of us here use it wad and 4 me i dun need 2 alter anything when i had the K&N...only thing i have 2 do with it is washing it... Evil or Very Mad

dansplace SG

Ain't no expert, so I will help where I can...

The ECU should compensate when the ecu is in its close-loop mode and uses the O2 sensor as an indicator for injector outputs. But when the ecu switches to open-loop mode (which I believe is dependent on throttle position), then the ecu will simply read of its fueling maps and compensation might not be present.

and also what is the difference when someone uses a piggy back ECU to change the mappings of the A/F ratio and someone who installs an fuel pressure regulartor?[/quote]

I dun use piggyback but I had a AFR in my car before I installed my open-pod. I had some lack of fuelling pressure which worsened with the open pod - i.e. not enough fuel pressure and with more air being sucked in.... not smart... kekeke . Only after I installed an aftermkt higher-flow fuel pump - everything was dandy.

tailslide SG

juz to add on to dansplace reply.

your ecu does give compensation in closed loop under part throttle. this is to make your car idle better/ maximize fuel efficiency/ better throttle response under normal driving conditions. however, when your ecu runs in open loop (under full throttle), it will basically read off a fixed mapping programmed by the manufacturer, which does not give any fuel compensation.

only way to stop the ecu from reading off this fixed mapping is to get a "piggyback" to "override" the signals the ecu is receiving/sending or to get another ecu which is tuned for your current set up.

in most situations, car ecu's from the factory tend to be programmed slightly richer under full throttle to safe guard the engine from running lean (one main cause of engine blowing), so having a better flowing filter sort of evens out the balance. a filter element should do little in any case to change the A/F drastically, unless u FI the engine or modify the internals heavily. Wink

dansplace SG

Hey tailslide,

From my understanding, the ecu switches over to open-loop at 20% or more TPS.

tailslide SG

dan, unlikely to be the case.

the open loop mapping existed as some form of a fixed "safe" mapping, designed to prevent things from going awry under full load. of course, having the benefit of a fully programmeable ecu also enables u to max out the potential of this map for peak power and torque.

at part throttle position, the ecu will continue to read off individual values of the lower load points and continue to make adjustments from the readings it receives. as load, rpm, air temp, intake velocity, tps.... etc all fluctuate too much at low rpm, part throttle, it would do the engine and driver more good when the ecu functions at closed loop to enable the ecu processor some leeway to make adjustments to make driving smoother. under WOT, the increase in these parameters are more steady and predictable (there is less fluction in throttle position since u've decided to floor it) and it is safe to follow the readings given in the open loop programme.

but then, i am stating in general wat ecu's are supposed to do under different load conditions. perhaps there are some which would do otherwise under even low loads such as 20% TPS. Wink