Fuel trim question

[B&Vperformance]

I just finished getting the fuel trims straight and when I turned Closed loop back on the trims went to crap but the car still ran great. Also I leave the LTFT's off. I never noticed a problem with this before. Any ideas why my trims would be thrown off?

Btw, this is through MAF tuning.

[Higgs Boson]

What fuel are you running? What mods? Did they go to crap at idle or when cruising?

[B&Vperformance]

Pump gas 93 octane.
403ci LS2 with LXR LS7 heads
248,254,675 in.,686 ex.112 +3 custom grind cam
3600 stall
545 rwhp 479 rwtq

The trims are perfect when CL is disabled but then shows +5 to +10 numbers when on but stil drives great.

[DSteck]

Lol. You don't have trims when closed loop is disabled.

[B&Vperformance]

Lol. You don't have trims when closed loop is disabled.

Sorry I meant other way round.

I read how you tuned MAFs thats the way I do it too but what about VE tuning? Do you disable CL, tune VE, and then turn them back on?

When tuning MAF you leave CL on and use MAF in HZ vs Dynamic airflow. Then copy paste special Multiply by % untill it where you want it right?

[Higgs Boson]

What is your stoich table set to? Try changing it to 14.2 instead of 14.7 (or whatever it is) and see if that brings trims in line. Tune with stoich set to stock, then adjust it for your fuel (E10 I assume) when you go into closed loop. Tune both MAF and VE in open loop.

[B&Vperformance]

I'll make it easy. This is my tune. The Stoich is set to stock. It has 60LB Fast injectors. I'm sure I just need to adjust the trims a bit more. Maybe I accidently didnt reset fuel trims on my last go.

Attachment 30672

[Higgs Boson]

like i said, change stoich to 14.2, reset trims, and check it, then get back to us.

[B&Vperformance]

Thanks going to do it now.

[B&Vperformance]

That seemed to be the ticket! Thanks a lot!

[IDRIVEAG8GT]

I see alot of people changing stoich fueling on big cam cars to a slightly more rich state, is this because the amount of overlap screws with the O2's and changing stock stoich values compensates for that?

[DSteck]

Changing stoich just cheats your airflow calibrations. The fact is nobody knows the true stoich value of the fuel they're using... They just come up with ways to justify what they are doing.

Changing from 14.68 to 14.2 is the same as adding a percentage to the VE and MAF values.

[IDRIVEAG8GT]

Changing stoich just cheats your airflow calibrations. The fact is nobody knows the true stoich value of the fuel they're using... They just come up with ways to justify what they are doing.

Changing from 14.68 to 14.2 is the same as adding a percentage to the VE and MAF values.

I understand. I prefer correcting through the MAF but that's just me.

[DSteck]

I understand. I prefer correcting through the MAF but that's just me.

I am the same way.

[Higgs Boson]

I hear what you guys are saying but after dicking with my car for 9 months last year and some this year, too I came to a firm conclusion.

Tuning with trims sucks compared to tuning with a wideband.
Tune in open loop with a wideband with the stock stoich setting. This effectively tunes your MAF and VE based on Lambda (or just use a Lambda PID).
If you go back into closed loop the stock stoich setting is no longer Lambda 1.0, your trims will be off unless you set the Stoich box close to your fuel.

Once MAF and VE are tuned with open loop you don't need to ever reconfigure them again for a fuel change (for closed loop operations).

[DSteck]

What are you smoking? If your O2 sensors and wideband aren't jiving, then you probably have a shitty wideband. If you tune the car in open loop with a wideband and then change the defined stoich AFR, you're going to throw everything back out of calibration regarding fuel delivery.

I think you don't quite understand lambda, AFR, and how they relate.

[Higgs Boson]

What are you smoking? If your O2 sensors and wideband aren't jiving, then you probably have a shitty wideband. If you tune the car in open loop with a wideband and then change the defined stoich AFR, you're going to throw everything back out of calibration regarding fuel delivery.

I think you don't quite understand lambda, AFR, and how they relate.

Ok....

Works for me and it appears it worked for this guy, too. It must be some good shit I smoke. Let me know, I share.

maybe I don't explain my reasoning well but my point is I tune with a wideband in open loop with stock stoich setting.

back to closed loop after tuning with the stoich setting adjusted to approximate stoich for fuel in tank and trims are on target. with the stock stoich setting they are off.

my car was originally tuned by a PRO TUNER. and the tune was a hack job. i trust myself much more now. i've tried and seen a lot of different things, read a lot of YOUR posts, other people's posts, etc and tried it all. guess what, whether you agree with me or not, what i said works. no hacked injector or PE tables. good VE, MAF, and timing tables. AFRs in line. no knock.

my wideband is a matchstick covered in oil tied to a string wrapped around my ear. do you think this is a good wideband?

[DSteck]

I'll respond to this at lunch. I don't feel like typing this out on my phone.

[Higgs Boson]

I'll respond to this at lunch. I don't feel like typing this out on my phone.

lol. whatever man. i sure hope you aren't planning a huge serious response. there are more important things in life. I'm out, like you, I have to work.

[DSteck]

I'm going to show you what you're doing by outlining the math of the PCM. Maybe you don't care, but the rest of the community probably wants to know what's really going on instead of continuing to just hack value for a desired output.