Tuning variences with the same tune same day (LEAN!)

[Phill]

*EDIT* sorry, car's a 2008 m6 corvette with the ls3, mods are intake, exhaust, headers, 230/234 cam, ect. Nitrous is on, but never turned on during this tuning

well today i was going to finish the car up and dial the nitrous in so I might be actually able to drive this piece before summers over. I ran the base tune with no spray to make sure fueling was right (havent driven the car in a bit)

It looked ok, its the scan #1

there were some lean and rich spikes, I did my normal histogram deal to tidy it up, and things just kept getting worse. Finally after 4-5 more tunes that kept getting leaner and leaner.... (even when making richer via airflow) I said fawk it, and put the original tune from the start of the day back in.... AND IT WAS WAY LEAN DOING THE SAME 3RD GEAR PULL... I am behind frustrated with this, I didnt want another full time job to tune this car but its turning into a nightmare.

Scan #2 is the scan of the same 3rd gear pass, about 2 hours later in the day with the same exact tune file.

I'll inlclude the tune.



Can anyone explain this to me? I mean 2 hours earlier in the same weather its a ok tune around my commanded afr, then after some other weird tunes going way lean, I put it back on and its lean too?

I then got mad and added 10% air to all values from 5500-8550hz and it did richen up (cars fuel system works fine) and i'll attach those logs. I did a run in 3rd and a run in 4th.

I noticed in 4th the car runs way richer then in 3rd? what gear should I be dialing in maf for?? If i dial in for 4th, 3rd will be lean?

I'm beyond confused, I started the day thinkig I would tune the spray, I ended up going backwards and ending up with a shit tune without the spray... almost to the point I'll pay to fly someone to calgary to get this shit done so I can enjoy this car again.

thanks for any help.

[DSteck]

Your MAF table is jagged as hell. It really needs to be smoothed out. You have cells of higher frequencies with lower airflow values than previous cells.

When running MAF only, there's a sort of lag with the MAF, and you'll notice higher gears will run richer. When street tuning MAF only, I typically do everything in 3rd gear to set it where I want. It'll be leaner in 1st and 2nd, then richer in 4th. Seems pretty normal from what I've seen.

You're getting deviations because your long term fuel trims are positive. Check your trims while in PE... Sometimes they are over 10%, sometimes just 5%. Positive trims get carried into WOT and will influence your fueling, negative trims won't. Get your trims negative everywhere and you'll notice that deviation go away.

[Billf6531]

I pm'd you.

[Phill]

Hmmmmm I smoothed out the MAF curve (and richened it up a little), and now my afr follows the commanded pretty darn good.

One other question I have, is in MAF only is it possible to get rid of these lean spikes after shifting? I'm worried that on the spray this might go boom?

[Phill]

Oh, I still have positive LTFT in PE, how does one get them negative?

[DSteck]

You have to tune your MAF everywhere to get trims into the negative if you want to prevent them from going into PE.

I think you can disable CFCO to help with the lean spike. I wouldn't stress over it that much though. You're seeing the lean spike from when you lift your foot off the throttle, it's just delayed because it takes time for the exhaust gas to hit the wideband and show a response to what's happening.

[Phill]

Cool, so i would assume adding to the airflow table (ie making it think there is more air and thus fueling more) would make the trims go more negative? Can it be as simple as multiplying the whole maf curve by a set value (ie 1.05 or 5%?) then checking things again? Wouldn't it be simpler for me to force open loop, dial it in, then turn back on closed loop? That should get the LTFT dead on?

thats cool on the lean spike, I was hoping it wasn't a issue, if I mess with the CFCO I seem to get it to hang rpm wise when i hit the clutch.

I also found my header bolts were loose.... I wonder if some air was getting in "leaning" out my wideband... I doubt it as there was no exhuast tick, but I tightened them all up anyways.

[DSteck]

You can tune the MAF in open loop, but I just use closed loop. Set up a histogram that logs LTFTs against MAF frequency. It should be Histogram 3 in the config I gave you (at least... I think I gave you a config). Highlight, multiply by %, and be on your merry way. Just remember to smooth the MAF curve... it needs to look like an actual curve with no jagged areas.

[Phill]

Oh-man, this all make soooo much more sense now! I dialed the LTFT in up to abuot 5500 hz and they are slick, between -1 and -3 during all through the range. Did some WOT passes, and I'm almost 100% parallel to the commanded line just 12.3 ish instead of 12.5. I'll get that tuned tomorrow.

How high HZ wise should one worry about the LTFT? I was thinking that ~5500 hz range seems about right.

Now I drive this car from 32*f to 110*f so I imagine tuning fuel trims today at around 70* was a good place to be, I should have lots of room for the LTFT and STFT to adjust for weather either way.


Man I feel better when things make sense. I'll be honest, I had no idea LTFT affected WOT fueling when positive.

[Phill]

Ok, I had some more good progress, I smoothed out the maf after fine tuning it, did a long drive, ltft's range in the -2 to -1 range. Perfect. at full throttle afr's range from 12.4-12.6 smoothly (commanded is 12.5)

I see no real KR

I decided to spray her, used the HSW interface to trigger it and retard 4*, ended up getting a pretty smooth AFR curve on the 100 shot of around 11.4-11.6 afr on the squeeze. I delayed the kit .1 second (rich on activation), and leaned out the top end (it got rich in a maf area I hadn't reached yet) and it looks real good.

On more night of running it through its gears on and off the spray and I'm calling it quits. knock on wood but it looks good.

I had never used nitrous before, I liked it, the 100 shot seems perfect after 2nd gear. The window switch, with the interface and shifter button interupted WOT switch seemed to work perfectly.

[carlrx7]

nice job, you seem to pick up the basics quick.