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AFR too high; how much more fuel pressure is needed?

KnappAttack said:
I have multiple sleds setup exactly the same, some idle at 12.0 and some idle at high 13's. All have identical setups in them. Craziest thing I've ever seen.

Something even crazier, you can increase the fuel pressure up, even go way up to 60 or even 70 lbs key on, you can just crank the regulator up bu y multiple turns and the idle AF doesn't go any richer. If you decrease the fuel pressure below the stock 44 lbs key on, the AF will go lean in a heartbeat, but increase it and nothing, it sits and idles exactly the same not fluctuating a bit or changing AF ratio whatsoever, but at midrange and WFO obviously it will richen up quite a bit like it should. I can go from 125% on the fuel multiplier to down into the 80% if you want to, but at idle, no change, someone tell me how that works.... The closed loop isn't supposed to work at idle, only when you get into track speed does the closed loop start working.
Click to expand...

Changing the pulse width of the injector signal? The ECU special cases engine idle management. I don't think it needs closed loop in this instance because many of the variables are fixed (throttle position, airflow, target RPM, etc). Just guessing.
 

you would think that if the ecu has a specific pulse width for an idle /rpm constant.... why would the increse in pressure not make richer???? baffles me as if pulse is constant then increasing pressure would deliver more fuel for that given 3 millisec opening. making afr richer.... but it doesnt , yet when we decease presure it leans it instantly.
 
max rolph said:
you would think that if the ecu has a specific pulse width for an idle /rpm constant.... why would the increse in pressure not make richer???? baffles me as if pulse is constant then increasing pressure would deliver more fuel for that given 3 millisec opening. making afr richer.... but it doesnt , yet when we decease presure it leans it instantly.
Click to expand...

Not saying its constant, just that RPM is a target and the only way to achieve that during idle (target RPM) is to modify pulse width because airflow is out of your control and what would you do, you could only allow more airflow which would raise RPM, not lower it. I was speculating that the pulse width is variable and the ECU has enough information to know how to do this properly. If for instance you start your sled at 10,000' then the ECU has to have a way to ensure that it can manage the system during that low air density condition and the only way to do that is to both modify pulse width and ask for more air, so it makes sense that the ecu could do the opposite which is to live with the air it has (base setting for throttle body) and reduce the amount of time the injector is active. When you decrease pressure there is a floor, you can't go below a certain threshold as the ecu cannot make up for the missing pressure, it can only moderate what is there. Hope that makes sense. This is just a guess and I am hoping that someone chime in and says 'no you idiot' it works like this. :)

In this theory, the easy way to test it would be to put a scope on the trigger pulse for an injector and change fuel pressure. That should instantly trigger a change in pulse width.
 
lol soo true, i just found that when the idle had afr in the 12"s the throttle crack was a little snappier compared to when afr was at 14.0... i look at it as im saving fuel and keeping the plugs clean as there is no load at idle and absolute perfect stoiyk is 14.6 soo it a clean burn idle!!
 
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