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PE Equivalence Ratio - HP Tuners help needed

Practical Reflash Tuning

Discussion and questions related to the course Reflashing


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Been helping my buddy with his drag mustang powered by a 6.0 iron block with twin 78mm turbos. I got him from 2.0 60ft 16 sec 1/4 mile ETs down to 1.38-60FTs and 9.96 1/4 times in 12 passes. ONLY using the AFR numbers in the scanner after a pass. No histograms nothing.

So there’s just a single number in the Equivalence ratio which I’m assuming is something his tuner set up for full throttle power runs. I’m trying to get the AFR err histogram set up so I can be more accurate and see which exact sites are needing adjustment and by how much.

So his car is set up for open loop all the time since it’s solely a drag car and does not street drive it other than around the block to test something he may have added or fixed as a quick check before heading out to the strip with the car.

i need to have a commanded AFR to be able to get the histogram working. So two questions,

1: can I set up the commanded AFR Equivalence table without enabling STFTs and LTFTs? As well as keep it in open loop

2: since HP tuners is reading off his lc2, do I enter the equivalence for lambda or AFR? I know if I use lambda I have to do it with the inverse function. However if I have to do it in AFR do I have to do stoich/wanted AFR? Ex: 14.68/13.5 or 14.68/11.8 etc?

Hi Damen, please see below:

1. Yes, this histogram will work regardless whether you're running in open loop or closed loop. When using this histogram to help dial in the SD table or MAF table I will normally set the ECM to run open loop so that the fuel trims aren't masking the errors.

2. You can use AFR or lambda numbers depending on your preference. You just need to make sure that you're logging both commanded and measured values in the same units otherwise the math channel won't work. I personally use lambda as that way we don't need to worry about the stoich value for the fuel.

Ok so how do I find out the equivalence for using AFR since his log is in AFR I’ll just keep it the same. Do I do the stoich of the fuel divided by the target I want to get the commanded for the equivalence number to put in the table?

Yes, just divide AFR by stoich and then use the inverse function on your calculator to get equivalence ratio.

Great! Got everything set up now, AFR error etc. Only thing is that as i pull fuel out of the idle area, for some reason he is bouncing from 11.5/12.4 to 14.5 and back down but does not hold a steady 14.6-14.7 he is on C16 at the moment. I was told by his tuner to look at the equiv ratio at idle. Where do i find this in the HP tuners? Is this that single line of cells that has the RPMS and you input different ratios across such as what you did in the PE section of the worked example on the SD car?