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Cobb Accesstuner Closed loop target afr

Practical Reflash Tuning

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Hello! First I must say your classes are a complete game changer. It’s all really starting to make sense and I can make some confident changes to my 04 fxt.

I have a question. It seems the closed loop is always targeting 14.7 afr. I’d like to run alittle richer in the cruise areas by my math around 14.04 makes sense for e30. Not neccsarry I’m sure as I’m not running into any knock but I wanted to give it a try. However there isn’t any “closed loop afr target map” in accesstuner that I can see. The only thing I’ve found that might work would be to change the MAF scale so that 0 volts was 14.04 as opposed to the 14.70 it’s set at now, of course I would shift the entire map by the -.64 as well.

I wanted to check in with y’all before I did that though.

thank you for your time!


So first, stoich AFR for E30 would be 12.99, so I'll use this number.

So this is a good example about why the AFR Scale can be problematic (or confusing). You're ECU doesn't know what fuel you're running, and what is it's Stoich AFR. Right now, your AF Sensor will show "14.7" regardless of the fuel used, because it is the "stoich AFR" which is equal to Lambda 1.00. If you change your Close Loop AFR Target map to 12.99 like you want, it would be be equal to Lambda 0.88 (12.99/14.7), so you would be running pretty rich. That's why using the Lambda scale is easier once you get used to it, as Stoich is always = to Lambda 1.00.

Right now, if you change fuel and run one that needs 12% more mass to achieve stoich, you'll find your fuel trim to be positive of that 12% at all time in close loop because the AF Sensor will detect you are running lean and will increase the injected fuel quantity. The problem will be when you switch to open loop, you'll be running 12% lean as the ECU won't take the feedback of the AF Sensor into account.

The best way to solve your problem would be to run an Ethanol Content Sensor and a flex fuel patch. Unfortunately, COBB removed these because of Project Green Speed.

Other options would be to adjust the injector or the MAF scaling to "trick" the ECU into injecting more fuel, to account for the different stoich ratio of the fuel you want to use.

Anyway, I hope it make sense!


As Frank said, when you get the hang of it, lambda is so much easier, especially with different fuel blends as oil refineries adjust summer and winter blends - on top of the normal variations in quality between retailers.

Because of the emissions issue, modern vehicles will run 'stoich'" by default to give the minimum CO and NOx in the exhaust gases. Without that, a lambda of 1.1-1.15 will normally give the best economy a "lean best'.

I may be missing something (rather likely) but the issue seems to be that you need more fuel to be injected but the vehicle's ECU limits the range that can be used? I would expect it to have a narrow band lambda for the ECU to correct the fuelling for wear, etc, and if so I would have expected any fuelling adjustment made to the ECU to 'stick', because it will still be a 1.0 lambda? At higher throttle openings, some manufacturers disable the lambda because they run the engine richer, and it's outside the emissions test parameters - is that the case here?

If there is a problem, is it possible to fit larger injectors with a flow/mS proportionally higher? Alternatively, increase the fuel pressure, which is a bit coarse, IMO?

I have a link g4+, Cobb eth sensor, fuel pressure sender, 4bar map sensor, and links iat sensor. Installing next week. Psyched to use SD, flex fuel, lambda, not have the restrictions of accesstuner software. I totally agree with lambda and understand why it’s superior!

Was hoping to try and understand a work around on this reflash set up for learning sake. Unfortunately accesstuner doesn’t let me set up my primary fuel maps using lambda. I can log the o2 sensor in lambda but the command fuel target and final is locked into afr as far as I’ve been able to find. As far as the o2 sensor scaling goes. It seems 0 is what is set as lambda with cells stretching out in either direction. So if I change that from 14.7 to x. Would that change what it’s targeting in closed loop to x?

I do have 1650cc ID injectors and ID rails, Teflon -8 lines and a walboro 450. So another possible option goes is saying, would be to change the flow at the injector level and then just continue to let the ecu do what it thinks it’s doing.

thanks for your time! Working within restrictions is fun, but I sure am excited to upgrade to what has all the freedoms(link)

Oh yes and why I did 14.04 is because I tested the fuel and it’s consistently only 12-13% ethanol. Do you use .058*ethanol content=lambda target drop?

I used the following method.

30% of 9 (AFR of pure ethanol) = 2.7

70% of 14.7 (AFR of gasoline) = 10.29

Added up together is 12.99.

Like I said, since Project Green Speed, you will be more limited with Accesstuner (and I haven't used the software since the update). Using your Link ECU will be way more easier for you!

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