Per cylinder fuel trims

[frank_ster]

Just a quick question, do the stock grand nationals lean out or richen certain cylinders ?

Just wondering if the intake ends up giving more air to certain cylinders .
Just because I'm still getting occasional miss fire at idle just want to optimize things

 

[earlbrown]

I have no idea what you mean by that first sentence, but....

Without a powerplate the rear cylinders tend to get more air than the front two and tend to run leaner.

 

[frank_ster]

^ yea kinda was wondering if the ecm is programmed with certain cylinders that get extra fuel.

 

[TurboBob]

The ECM internally has the ability to send a different amount of fuel to each cylinder. But the stock program doesn't.

Bob

 

[Heisenberg]

And we will expect that software change by the morning Bob.

And - Why can't you just update our chips with the latest bug upgrade patch backdoor entry every couple days like Mister Softy does to my PC?
Wanna know.

 

[frank_ster]

i have megasquirt so i have the ability to put or pull fuel from each cylinder.
but i don't have individual o2 sensors or egt sensors. so was hoping to mimic that the grand national ecm does, i would think it would get me a bit closer.
so do any of you know what the stock % additive to the rear cylinders is?

 

[TurboDave]

i have megasquirt so i have the ability to put or pull fuel from each cylinder.
but i don't have individual o2 sensors or egt sensors. so was hoping to mimic that the grand national ecm does, i would think it would get me a bit closer.
so do any of you know what the stock % additive to the rear cylinders is?

I'm not sure you understood what Bob said. The stock ECM doesn't do individual cylinder correction, it's not in the software. So there's no numbers to give you.
Besides, If it were me, I wouldn't even attempt such an adjustment with your megasquirt without proper data inputs to read each cylinder. Guessing at things only breaks things. You'll need to probe each cylinder's output (either via individual widebands or EGT's) to know what 's happening.

We have individual cylinder control in the new SD2/Powerlogger system, but as I said. I wouldn't fuss with them without being able to measure what's happening.

 

[TurboDave]

And we will expect that software change by the morning Bob.

And - Why can't you just update our chips with the latest bug upgrade patch backdoor entry every couple days like Mister Softy does to my PC?
Wanna know.

It's already available in the SD2/Powerlogger system.

 

[TurboBob]

It's already available in the SD2/Powerlogger system.

 

[frank_ster]

I only want to do this at part throttle and idle to clean things up a bit.
I gave 10% more to cylinder 1-2 and 5% more to 3-4. Keep in mind my throttle body is on the bell housing side. It seems to be a bit better but still a sucky idle still stalls some times.

 

[TurboDave]

I only want to do this at part throttle and idle to clean things up a bit.
I gave 10% more to cylinder 1-2 and 5% more to 3-4. Keep in mind my throttle body is on the bell housing side. It seems to be a bit better but still a sucky idle still stalls some times.

You're doing this without any way to measure what cylinders need what, or don't need???

What's your target air fuel ratio in the idle cells? How close is the wideband to maintaining target?

 

[frank_ster]

currently i;m idling at about 13.7 .. i have tried everywhere from 11.5 to 16-1.
the actual afr stays +-.2 from what i set it to unless its super lean or rich it will start oscillating and the engine will start surging.

all of the other engines i have megasquirt on are super steady idles and they idle at 14.7 even the series 2 supercharged engine was very steady.

but mine .. always idles like a brigs and strattion with a champion spark plug ..

and yes i taken away fuel from some cylinders at part throttle area .. and not really worried as i have driven for a tank of gas at 16.7-1 afr and didnt melt anything down.. but the car was not any better on gas. i found the sweet spot to be about 15.2-1 afr for best fuel economy.

i always though the miss at idle was because of batch fire .. but i have been running sequential for 2 years now and its not much better.

another question .. do you guys know when the sequential injection is timed to? end of injection at valve close? or beginning of injection when the intake closes? i have tried it around the range and its the same everywhere except for around the time the injector closes. as i can only suspect the shock wave is taking some fuel and throwing it back to the plenum and then the next cylinder is taking it and getting extra fuel.

 

[TurboDave]

I emailed GNX405 on this board. He is running megasquirt on his LC2 powered Mazda so hopefully he'll chime in and possibly help.

 

[BEATAV8]

I only want to do this at part throttle and idle to clean things up a bit.
I gave 10% more to cylinder 1-2 and 5% more to 3-4. Keep in mind my throttle body is on the bell housing side. It seems to be a bit better but still a sucky idle still stalls some times.

that sounds like an awful lot, even at idle. I would have thought 1-2% or along those lines? I haven't messed with it yet though.

 

[frank_ster]

well 10% would be about 1 afr . it really depends on the dynamics inside the intake. if it was 1-2% it wouldn't be any kind of issue.