LTFT's

[tbot]

I had 0 LTFT at idle when I tuned my car...and even w/o a tune I always saw 0 LTFT and STFT at WOT regardless of what mods I had. WOT is open loop, not closed loop, so MAF calibration doesn't matter. The ecu is then just trying to meet target AFR's based on the top O2 sensor, not based on MAF voltage, so fuel trims should be negligent at that point.

[RichB]

Ok, we all know that our cars target an AFR right? What happens when you have an AFR that is overshooting a little? Yup that's right, the ecu adjusts fuel trims. It starts with the short term trims and if it registers similar numbers for long enough time it shows up in the long term trims. I have done hundreds of logs and watched it happen. Maybe you are seeing 0 long term because your short term hasn't stayed steady enough. But one thing I do know is the ecu uses both long term fuel trims and short term fuel trims to manage AFRs

[tbot]

You are right, but all that is only true in closed loop operation. Once in open loop it ignores the fuel trims, aka going WOT.

[RichB]

So going WOT is supposed to get you into open loop ops? I always register a fuel trim number at WOT. Apparently I never go into a open loop situation.

[tbot]

WOT = open loop you should only see 0.0 for trims at wot

and your dashhawk will tell you if you're open loop, closed loop, or load based open loop.

[RichB]

I don't think that's true. The fact that you can adjust the closed loop MAF calibration should point out that it is used somewhere. Maybe the Cobb maps force the closed loop to be used because that's where mine stayed.

[tbot]

You must not understand cause you keep getting this fvcked up.

Closed loop is used all the time, unless you go WOT, then its open loop. So driving around town, idling, cruising on the highway...thats all closed loop. SO yes its used, most of the time.

Open loop is used only when the throttle is all the way open, aka WOT.

[RichB]

Maybe your not understanding what I am saying. When I had my Cobb map, I never saw open loop at WOT which is why I said, maybe Cobb forces closed loop (even at WOT). On a stock tune you may be correct but I haven't data logged on a stock tune so I can't confirm it.

Make sense now?

[RichB]

I just read something very interesting about Open Vs Closed loop operation. You can be in closed loop even at WOT. The ECU only switches over to open loop when you mash the gas and go WOT. So If you roll into it like I do a lot, you will stay in closed loop ops. This is why I think when you are doing MAF cals the instructions tell you not to mash the gas.

Anyway back to the original question by kingtut, your fuel trims look a little squirly and I'd check all of your connections. If you hit +20 or -20 on LTFT you will get a CEL and from the looks of it you are dangerously close.

[tbot]

Fair enough, but same thing happened when I had my AP...and as far as cel's I've seen -24 w/o a cel, I believe the limit is 25.

And Cobb doesn't lock out open loop. Open loop can also be triggered by load, which is the "l" in the bottom right corner of your dashhawk, so even rolling into to wot still should put you in open loop.

[erod550]

No Rich. If you stayed in closed loop when you went WOT, no matter how you got there by mashing the gas or easing into WOT, your engine would blow up. Closed loop is about fuel economy and does everything it can to hit 14.7ish AFR. If you were at 14.7 AFR at WOT, your engine would explode. No matter how you get to WOT, you go into open loop when you get there. Now the Cobb maps have a setting that tells the ECU at what throttle position to enter open loop and that will vary depending on your tune, but you are definitely on open loop when you go WOT, which has a completely different set of AFRs it tries to hit.

[chickenwafer]

I had 0 LTFT at idle when I tuned my car...and even w/o a tune I always saw 0 LTFT and STFT at WOT regardless of what mods I had. WOT is open loop, not closed loop, so MAF calibration doesn't matter. The ecu is then just trying to meet target AFR's based on the top O2 sensor, not based on MAF voltage, so fuel trims should be negligent at that point.

You must not understand cause you keep getting this fvcked up.

Closed loop is used all the time, unless you go WOT, then its open loop. So driving around town, idling, cruising on the highway...thats all closed loop. SO yes its used, most of the time.

Open loop is used only when the throttle is all the way open, aka WOT.

OK, I know I haven't tuned Speed cars before, but I have tuned RX-8s extensively using the Cobb AP, so I know a few things here about how these ECUs work.

There appears to be some confusion about open and closed loop. It simply means, in closed loop, there is o2 sensor feedback, and in open loop, there is NO o2 sensor feedback. That's it. The ECU never ignores the MAF sensor, because that is how the ECU calculates load. Try unplugging your MAF sensor and driving around and see how the car behaves.

MAF Calibration ALWAYS matters! If your MAF is scaled incorrectly, it will throw off your entire tune, because MAF cal is how the ECU determines Load, and if it is off, your ignition timing, fueling tables, boost duty cycles, etc will ALL be off. The ECU ALWAYS references the MAF cal!

It is true, at WOT, the ECU ignores precalculated fuel trims, and has no way of adding new trims because the engine is in open loop and is NOT referencing the factory o2 sensor.

Secondly, there are quite a few determining factors in when the ECU exits closed loop and enters open loop (all of these are definable with the Cobb AP), which includes tables for RPM, Load, etc. It's easy to get into open loop without even hitting boost in a Speed car, just based off RPM. At a certain RPM the ECU will go into open loop.

The really understand why and how all this works you need to have a full understanding of WHY open and closed loop fueling methods are employed, otherwise it's like trying to do an algebra equation on a calculator without knowing the formula I'm not going to get into the who tuning methods now, because I honestly don't have the time (hint; it has to do with engine speed).

Since I haven't tuned Speed cars I can't comment firsthand, but whenever I tune and RX-8 I always shoot for a LTFT and STFT of 0 at idle, and I usually get it. It requires a good deal of MAF calibration tuning, which can get pretty tedious. But I also have a good method for doing this (and tuning your entire MAF calibration range) if you would like to know.

The reason a Speed car can come off the lot with negative or positive fuel trims is because Mazda had made ONE TUNE for EVERY Speed3 in the country. This is a pretty large blanket style tune, and obviously what works for a Speed3 at sea level in San Diego isn't going to work as well as a Speed3 at 5500ft elevation in Denver.

[RichB]

Chicken, I really appreciate the response. I was simply pointing out that I have seen LTFTs at WOT before and they aren't always 0. Maybe I wasn't meeting the criteria to enter into the open loop charts when I was doing my logs. I'm sure there are alot of criteria that has to be met. I'm not saying in any way that I know more about this stuff than anybody but I know that it is possible to get WOT fuel trims becuse I have. I knew that there was more to the story and I'm glad someone pointed it out. Thanks again!

[kingtut]

Good information in here.

I checked all attachments on the BPV and didn't find anything that stuck out. The allen bolt on the bpv, where the recirc hose connects was a bit loose-- but I don't think it was loose enough to cause the issues I'm seeing.

I'm going to put the stock bpv back on and swap the TIP and intake too while I'm at it. Then check my readings so I can have something to compare to.

Anyone know where I can get a schematic/instructions on how to re-install the stock intake?:huh:

[tbot]

Pay me and I'll come over and do it for ya

Edit: you would also have to pick me up from the closest and then get me back to a light rail station when I'm done