Ok im pretty new to this whole tuning thing but i was thinking and wondering why this doesnt work.

Say you have an aftermarket ecu like the aem one. Now lets say you also have a very accurate wideband 02 sensor. Why in theory can you not say i want this AFR at this load at this RPM and it does it. With an accurate 02 sensor couldnt you just feed of that constantly. If the ecu sees rich it cuts fuel till its where you want your AFR to be. I mean isnt that what an open loop system is?

Now things like idle and idle enrichment i can understand you having to set but after thats over why can it not just do what i said earlier?

Just thinking so any info yall have to tell me im an idiot or whatever is completely wanted.

Thanks

 

The aem CAN do this to an extent in two ways:

you can Automap which uses a wideband o2 sensor to tune the fuel map to a desired AF ratio that you specify for each RPM and Load point. This takes a long long time becuase the aem can only make small changes at a time to be accurate. you can do it your self much faster with better accuracy.

The EMS car run closed loop O2 Feedback as well. normally on your stock ecu, the front narrowband 1v o2 sensor is used to correct low load fuel delivery and maintain a 14.7 AF ratio. You "can" enable o2 feedback at all loads on the EMS and specify a boost freindly 11.5 AF (whatever you want in fact) at the boost loads.

The problem is that the EMS cannot think for you. if the base fuel map is too far away from the AF ratio you want, the feedback will constantly overshoot the desired AF ratio. IE:

you want 12.0 AF at all boost settings and set that in the o2 feedback map. BUT your base fuel tuning is completely F'd up and would run 9:1 without the o2 feedback on. You turn the FB on and now that car cycles between 11.0 and 13.0 trying to hit 12, but it's not consistent and the AF is bouncing all over the place. Not a bandaid for bad tuning.

 

So what your saying is that if you can get close guessing, then with 02 feedback it can make up the little difference that your off?

And why would it fluctuate between those, can it not process it fast enough.

Also is there a place where i can read up on how you go about tuning it yourself or could you give me any advice?

Thanks alot man

 

There is all the information you need to become an EXPERT ems tuner on the EMS message board at www.aempower.com. between that site and reading the manual atleast once you should be able to understand the thing well enough to get started.

The main reason the ecu will fluxuate is the nature of the beast so to speak. it's there to correct a differenace AFTER IT HAPPENING. There is no way for the ecu to know what the AF will be in advance for any specific pulsewidth/load/rpm. the feedback can only try to help correct when the actual AF is not what you want it to be AFTER it see's the differance. The amount of tuning of the feedback system to be able to run a specific AF all the time with no fluxuation is more tuning that it takes to just set the fuel map correctly to begin with.

what Im saying is that you don't GUESS on fuel delivery. start out with a basemap that is known "way to rich" and manually lean it out while watching the wideband during a 3rd gear pull. tuning the fuel map on a boost compensation EMS takes about an hour of driving around. just as simple as tuning an AFC.

go search on the EMS board for these terms:
boost comp
automap
02 feedback

also look for posts from Blak94GSX and BLKMGK they are smart guys and you can trust thier advise.