I have been doing my SD open loop tuning and thought I was pretty much done so I reenabled my closed loop by setting the temps back to stock. I didn't like how the AFR's were going so I set the temps back to 250 but i'm still getting LTFT's with idle throttle I get -.8/-1.6 and does not change and at other than non idle I get 5.5/3.9 I don't know why i'm getting fuel trims with closed loop disabled?

 

If you are using HPT, open up the VCM controls in the scanner, and on one of the screens there is a button to reset the trims. Push that while it is connected to the car (and it is running), and your fuel trims should zero out.

Using long tube headers by chance?

 

Sweet i see it. Have to try it and see how it works. So even though I have closed loop off will those fuel trims still effect it?

 

Yeah...if you are still seeing those trims, it is affecting your tune. Always a good idea to look at them even if you are running open loop just to make sure there isn't anything funny like that going on. Although that really isn't all that funny. More like "run over your dog, ha ha" funny.

 

Thanks that makes sense cause my tune went to crap and now I know why. Really though what would be the advantage of putting it back in closed loop. I am trying to set my idle and cruise to 15.5AFR but when you re enable closed loop it will not go to this it will go to 14.7 right? So there is not advantage of closed loop?

 

i thought when you set the stoich to 15.5 or whatever you choose, that would be where it stays in CL.

Chris

 

In closed loop, the PCM will aim for whatever Stoich is defined as...it is all related to that little box that has the stoich value in it. From what I know of the stock O2 sensors, they are only good around 14.7 or so...I don't know what will happen if you change that little box to 15.5 or so to get what you want in closed loop (other than all of the other fueling calcs will be thrown off if you do).

FWIW, my narrow band O2 sensors were going to hell in a hand basket with my LT headers, so I run in constant open loop now. I run at 15.5 cruising, 14.7 with a little more throttle, and 12.5 leaning out to 13.0:1 in PE mode.

However you decide to do it, just tune it like you want to drive it.

 

If the stock O2's are only good for the 14.737 or whatever ratio.... Then would you have to get a wideband and run it in simulated narrow band mode to operate it at a different ratio?

 

That is one possible solution, but not many people have tried that, so I haven't heard all sides of that story. The obvious (and quick) solution is just to let it run in open loop.

 

Ok turned my closed loop back on. I did a little diff approach this time. I set my whole OLFA table to 1.0 commanding 14.7 and then I did my VE table in SD to get close to 14.7 then i reenabled my closed loop and got my LTFT's all within the +/-5. But now i'm gonna work on my PE. How would you do this I want to enable my PE at 75Kpa with like 1000rpm delay. And what would be the PE values for 12.5 and 12.8? So when I put my 12.5 and 12.8 commanded in my PE table then I just do runs and tweak my VE table until I get my desired PE AFR right?

 

Your commanded stoich (what is in the box) divided by the multiplier (1.13, or whatever) is what your new commanded AFR will be in the PE table.

I honestly have my PE set up to come on at around 50-55 kPa, and usually 40% or a little less TPS, and no delay whatsoever. When I want the extra fuel, I don't want to wait for it to ramp in.

Basically, just set it like you would drive it on the street, and keep tuning that way. You don't have to have your PE disabled to dial in your VE table...the histogram works by reading off of the commanded AFR PID in the scanner. Whenever it changes (like going into PE mode), it automatically takes that into the calcs to give you the % difference. See where you are when you do that, and tweak your VE table just as you would driving around part throttle.

 

****...forgot to ask. You are using a wideband O2 sensor, correct?

 

Yeah I have an innovate wide band. Ok so I set my delay to 1000, and my Kpa to 75, TPS to 35, and a 1.166 in the PE table from 800rpm to 4400rpm, 1.148 from 4800-5600 and then 1.166 from 600-7200. Ok so then pretty much when I hit 70Kpa and above 35%TPS i will be in PE mode. But then if you AFR is off which I think they are how would I modify to fit the commaned in the PE table.

 

Okay...if you are running in SD (open or closed loop), the only table your PCM references is the VE table (since the MAF is no longer active) to figure out how much air it is ingesting (the IAT and MAP get factored in as well, but those are real time values, not look up). You tune WOT just like you do part throttle...do some runs, and see what the AFR % Error is. Copy, Paste Special into the VE table, lather, rinse, repeat. What will happen is that once you get your VE table dialed in correctly, whatever you command in the PE table will be what you get (so if you want 13.0:1, that's what you get). The trick is that you need to have the PE table set up exactly how you drive it.

The PCM does some back calculating of some sort. For example, if you set your OLFA table to 13.0:1 across the board and dialed in your VE table, when you set it back to stoich (1.0 commanded), and do another log looking at your AFR % Error with reference to the VE table, you will find that your VE table is off by more than it should be. I don't quite understand it, but that is how it works. That's why it is important that you tune your car to the AFRs that you want when you drive it on the street. If you want it to cruise at stoich, tune it open loop to stoich. If you want to tune WOT to 13.0:1 across the board, you need to make sure you are commanding 13.0:1 when you are tuning open loop @ WOT.

You can either do this by setting the OLFA table to 13.0:1 from a certain MAP (75kpA+ in your case) up, or the easiest thing to do is to set your PE table up so that when you get to that certain MAP, it will command it for you (no need to touch the OLFA table). When the PCM detects WOT, it looks at a couple of things - one is your OLFA table at whatever ECT and MAP you happen to be at. It also looks at your PE table. Whichever value is richer, it picks and aims for that. That's why you can set the OLFA table to 1.0 across the board, leaving PE enabled (and at whatever settings you desire) and it is perfectly safe since the PCM is going to aim for the richer value (in this case, your PE table).

Does that make any sense at all?

If you want to see it, set your PE table how you want it, and set the OLFA table to 1.0 across the board. Make sure you are in open loop. Give is some gas, and watch the scanner (the table) and make sure you keep your eye on the "Commanded AFR" PID. When you get to the PE enable settings, you'll see the Commanded switch from 14.63 to 12.5 or whatever you have it set to. That is also what your AFR % Error histogram will reference, so you'll be able to modify your VE table as necessary.