Timing and fuel trim

My tune hasn't been getting the gas mileage my handheld used to. I emailed nelson and he told me to check the timing/fuel trim. I have no idea what "good" values are. What do ya'll think?




Alright, at idle, timing is about 20* ltrim is about 4.6

At cruising speeds (didn't change much between 50 and 70) timing bounces between 28 and 40*, seems to display 34.5 more then any other number.

At same cruising speeds, ltrim b1 was 6.2, ltrim b2 was 5.4

Whenever WOT, ltrim b1 is 5.4, ltrim b2 is 6.2, and timing is usually between 21.5 and 24 (seems to change lil depending on rpm/ outside temp/etc)


These numbers are all from my aeroforce interceptor.

ltrims seem high to me.

is that a simple tuning thing? or is it possible something else is wrong (though I doubt it, gas mileage seemed to drop pretty much overnight...well after a week when I finally stopped flooring it all the time lol)

It's a tuning issue. What does your AFR look like?

don't have the wideband yet :(


The aeroforce has o2 readouts, but those go all over the place. I have a autometer narrowband gauge, tempted to hook it up to the front 02s until I can afford the wideband (didn't think i'd need it until the cam/heads go in)

I'd have a look at your AFR when you can.

Those values aren't high. The high limit is 25+, it has plenty of room for adjustment before it sets a code.

Get in any stock vehicle and look at the ltrims, they will be between 0 and +10.
The ltrims are there to correct for conditions that are not controllable.
One day they may be negative, the other day positive.

So many things will affect ltrims: fuel pump, filter, injectors, maf, fuel, o2's, etc.

If I had the truck here (which it will be soon), then we'll tune until they are -5 to 0, but for any truck with his mods, it's perfectly acceptable.

you'll have it there? Allen, are you stealing my truck? I'm in IL, don't think that'll be happening, unless I win the lottery and can afford a turbo lol

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Originally Posted by oleshifty

you'll have it there? Allen, are you stealing my truck? I'm in IL, don't think that'll be happening, unless I win the lottery and can afford a turbo lol

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haha, wrong truck sorry, but still come on down, lol

If you want them at -5 to 0, then I'd say +5 is high. I was just comparing to my logs and based on mine, +5 is high.

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Originally Posted by pl4yboy

If you want them at -5 to 0, then I'd say +5 is high. I was just comparing to my logs and based on mine, +5 is high.

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I guess it depends on what you're comparing it to then, right, cause i'm comparing it to 25+.
If you get your ltrims at 0, then i guarantee you at one time or another , your ltrims are positive.
Ltrims are meant to go up and down and adjust, you just can't help it.

Just like KR is normal under certain conditions.

But if your Ltrims average at +5 or +6, it's pretty possible they'll hit +10... which is a lot higher than -5...

Ive always heard that ls motors love 13.1 far in pe mode. Is that not right?

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Originally Posted by o2camaross

Ive always heard that ls motors love 13.1 far in pe mode. Is that not right?

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ya, i'd say that's a good a/f to shoot for. what do you have that ls3 set at in your sig?

It's a stock tune other than a few Dtc's disabled and tm removed. I want to get a wideband before I start tuning it

Got my wideband in today.... idle/ cruising I'm around 13.6-13.8 at wot, 11.9-12.3


thoughts?

cruising looks fine, as long as cruising a/f ratio is between 13.5 and 15.0 it's ok, it's hard to get an exact on cruising because it's going to be up and down constantly.

wot is a tad rich, we'll need to lean it out a little.

If he's getting good number of cell counts it will average it out and 13.5 is rich at cruise, you only really need richer afr when in PE mode. You can safely go to 15 at a cruise then when you hit PE mode use 13.1, and 12.7 at WOT. Best bet is to tune using your stock O2 sensors and then you will need a Wide band to tune your PE/WOT. You want your LTFT's in the -5 to 0 range, if your in the + that means your lean and it will carry over the correction into PE so will throw off your tune. But tuning using LTFT is actually pretty easy, and pretty accurate using stock Narrowbands.

id rather have a +1 or + 2 then having a rich condition of -3

in cruise mode timing should be high 40s to low 50s with no load, slight load timing decreases but should still be high 30s to low 40s

keep working at it till the MAF is next to zero for error and fuel trims are around 0 thru +3

this is where your mpg will come around at. not enough timing will also increase EGTs!!!!!!!!!!!

If you have negative LTFT when you hit PE mode your O2's will lock and it will not correct. You will be going strictly off your commanded, VE table and MAF if your using it. If you have positive LTFT when you hit PE mode it will carry over into PE mode and sometimes can be tricky nailing it down because you will get corrections in PE mode if your positive on your ltft. You can have negative LTFT thats no biggie, don't mean your rich because it will correct to what you have set for stoich anyways. But you tune it the way you want everybody is different. Thats why you work your VE table to get between 0 and -5 but as close to 0 is ideal. All mine are between 0 and -2.

Quik +1 on what Pavetim said, you want your ltrims slightly negative during cruising and anything not in PE mode, so that when your foot goes wot, ltrims go to zero, then you can nail down the a/f ratio and make commanded = actual.
If they are positive, you can't do that.
Having the ltrims positive just to richen up wot is more work and you won't always have what you're commanding in the end.

Pavetim, I completely understand what you're saying, the only statement that I... Is that you have to scale your MAF table to get ltrims negative and positive as well during non PE cruising. The VE table is mostly used in open loop and cold startup, then you scale the maf after the engine warms up.

There's a little more to it, but maf is used to scale ltrims during operating temps, ve is used for open and cold startup.

Oh yeah I do the MAF at the same time as the VE table too, forgot to mention that. You want the MAF freq correction factor as close to 1.0 as possible too. Sorry thought we were just talkin about trims. But yeah for people keeping the MAF you can tune your VE table using LTFT, PE using WB, and MAF all at the same time if you've got the right calculations.

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Originally Posted by Pavetim

But yeah for people keeping the MAF you can tune your VE table using LTFT, PE using WB, and MAF all at the same time if you've got the right calculations.

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Details? First I've heard of that, but I'm still new to this.