Lean mixture when in o/l

[THEFERMANATOR]

I have had to start driving my Tahoe because my Suburban is down, so now I have to break down and fix my tune in it. It's my 99 Tahoe with an L31 5.7l vortec, marine intake swap, 0411 PCM swap, no EGR, and 75mm throttle body. I've had issues with it since day 1, but with alot of help from here, it's at least driveable. From day 1 I've had problems with it when cold running in open loop, it wants to stall when you give it just a little throttle.

For those not familiar with the 5.7l vortec, the stock throttle body necks down from 75mm to about 69mm right under the throttle blade, and they have an air foil mounted on them that basically makes only 1 side of the throttle blade let air in until about 1/4 throttle. I'm running a 454 throttle body which is a straight 75mm bore with a flat blade, so at low throttle it lets in considerably more air much faster than stock did. With alot of help in this thread https://forum.efilive.com/showthread.php?29111-larger-throttle-body-tuning ,the off idle response has been good, but when cold giving it just a little throttle it wants to stall.

After finally getting my wideband installed I found when its cold in o/l, Ive seen it go as lean as 18.7:1 so far, and it hasn't even been cold out, so I'm pretty confident my issue is a lean mixture when cold, and I have a feeling it goes back to my throttle body that lets air in so much faster than the stock one did. I'm getting ready to try and do some logs to correct my VE table, but is there any other tables I should look at for this extreme lean condition when cold? I don't think my VE table is that far off because my fuel trims are normally within 0 to 3, but my wot afr's are running 11.6-11.8:1, so I know it needs a little work. I'm just at a loss here coming from diesel tuning to gas tuning.

[statesman]

Does that vehicle have a MAF sensor fitted?

[THEFERMANATOR]

Does that vehicle have a MAF sensor fitted?

Yes, everything is stock except for the intake swap, it even has the stock cats on it still. I know it needs some VE corrections, but I'm at a loss where to begin with it for this going lean when it is in open loop cold. It ONLY does it when you give it a little throttle. If I get on it it doesn't seem to do it, let off the throttle and it immediately smooths back out, or once it gets to closed loop it never does it.

[statesman]

Try running in MAF only mode and see if it still does it.

[Supercharged111]

He's going through the same thing I did (and while mine isn't perfect, it's MUCH better than it used to be). With the 411 and stock intake, the truck runs just fine (with a 350 van base tune, can't speak to a stock LS base tune on a 350). Once you swap that marine intake on it's a whole 'nuther ball game. The injector trajectory is not nearly as good, so ends up spraying a bunch more fuel on the intake walls than the factory L31 manifold does. It's the transient fueling that needs to be addressed, particularly the impact factor tables. If VE or MAF aren't right, it'll exacerbate it, but in and of itself altering that table alone makes a world of difference. I started here and went down the rabbit hole.

https://forum.hptuners.com/showthread.php?10872-Let-s-discuss-Transient-Fuel

Went a little too far and ended up over-fueling at tip in at lower elevations (likely exacerbated by the tune at the time, Statesman probably remembers my calc.VET blunder from last year). BLUF: it's the delta between cells that makes the difference, doing global bumps isn't nearly as effective. I also found that, once it got down well below freezing, the truck lost that hesitation. It would come back as it warmed up to less cold, then slowly (mostly) go away when fully warmed up.

[THEFERMANATOR]

Now that the hurricane cleanup is done, I'm back on this. I went through and did the calc.vet and it did not help my going lean on initial throttle application when cold in O/L. It doesn't seem to stay lean as long, but it still goes up in to the 17's when I barely touch the throttle. It DID help throttle response when it is warmed up though. I'm getting ready to do another log on it as I went from LTFT of positive 3-6 to now LTFT in the negative 4-6 range. When I switched it to MAF only for the calc.vet when doing the log, it made NO difference with it going lean, and I also noticed my LTFT trims went higher in to the positives. It also added ALOT to the VE table in the low RPM range(IIRC close to +12% in some areas).

I'll look in to the transient fueling tables. I also need to look in to reducing the knock sensors sensitivity as it is pulling considerable timing out in some areas, but there is no audible knock heard ever. Is calc.vet or calc.maf the recommended method? Or use both?

I need to get a general grasp on this stuff as a friend of mine is doing an LH6 swap in his and needs me to tune it for him. This is making me really miss diesel tuning.

[Supercharged111]

Give this one a read as well, hquick also ran a marine intake.

https://forum.efilive.com/showthread.php?9127-Tuning-the-transient-parameters

Looks like we can't tag folks on the forum? I think he just came back from the dead here recently.

I've gotten audible knock exactly once on my truck. I've never felt the need to monkey with knock sensor sensitivity, I just try to not have any KR but there's always a trace here and there it seems.

For a lean cold idle (make good and damned sure VE and MAF are correct first), I just tried modding A0008 the other day and initial results are very good. Do you have a COS or not? If not, these values will be in B3647. What happens here, just like with the transients (because of the marine intake), is that with more fuel clinging to the walls longer, you have to inject more fuel to get it into the cylinders for combustion. Like tip in, this phenomenon gets worse the colder you go. For A0008 I bumped a couple cells by 5 and 10%, watched the weather and wideband the next day going to work, tweaked based on that, and logged the next day. I was damn close just like that, but I tweaked a little more and it hangs right around stoich now on a cold, open loop idle. I used the same log to tweak on the desired airflow tables but they were already pretty damn close. I believe statesman had something to do with that.

Here's Swingtan explaining all the transient tables in detail.


Further to that....


B3406: Impact Factor

Is a fuel correction "adder", so it increases the amount of fuel injected. It is calibrated via ECT and MAP to allow for different corrections based on temp and load. This table tends to have greater influence on smaller throttle movements rather than slamming the throttle open.

B3401: Evaporation Time

Tells the PCM how long it takes for the fuel left on the wall to make it into the intake charge. Again, this is a "correction" factor, not an actual figure for the evaporation time. Higher numbers here will extend the time that B3406 is used for as it indicates a longer evaporation time correction is needed. again, it tends to have more influence on smaller throttle movements.

B3426: Stomp Compensation

This tells the PCM to inject additional fuel when jumping on the throttle. Think of it as a pump jet in a carby based engine. As would be expected, bigger numbers = more fuel.

B3428: Stomp reduction

This tells the PCM the rate at which the "stomp compensation" is ramped out. Higher numbers result in a raster ramp out.


So for a lean tip in, I would look at....


Increasing B3426 to give a slightly rich spike at tip in spike
Adjust B3428 to blend the rich spike into the normal commanded fuel. Fir the spike goes, rich-lean-commanded, increase the factor to stretch out the rich spike. If it stays rich too long, reduce the factor to lean it out quicker.


For the rich spike at throttle close....

I wouldn't worry as much, but it can cause issues if you are running CL and the STFT's pull lots of fuel just prior to the throttle being snapped open. You could try reducing the values in B3406 and B3401 for the cells effected. This would normally be in the very low MAP cells, but may need some correction higher up to "catch" the rich spike earlier on.

If you really want to try it out, you can also mess with the Injector timing to mess with dynamics. The basic rule here is...


the earlier the injector fires, the more time the fuel has to evaporate


So an early injector event results in more of the fuel being used for the intended induction event. ( IE. less fuel left on the wall )

I've done some testing with firing the injector just after the inlet valve closes. Doing this you can pretty much zero out the impact tables, but you may also miss time the throttle stop fueling as the injector has fired before the PCM signals it needs stomp fuel.

I've also fired the injector as the inlet valve opens, it makes the stomp fueling pretty good, but needs lots of work on the impact tables to get things working.

Also remember that at full song, the injectors will be open for longer than the inlet valve is open......

Simon.

[THEFERMANATOR]

No COS, just an 0411 loaded with an 02 van tune modded to run dual electric fans. I couldn't find B3647 in my tune file. I thought maybe it was an injector table since there is no stock tune file to get all the injector data from for the marine injectors, so I used the 02 LS1 data(they flow the same, are the same height, look the same, but use a different plug). The AFR will be right on idling, but give it just a slight touch of throttle cold, and it goes LEAN, let off the throttle, and it smooths right back out. I did port my marine intake so the injectors are not shrouded like a stock one is(not sure if this helps or not, but I couldn't bring myself to put on an intake with so much material blocking the roof of the runner).

[Supercharged111]

Assuming the truck runs stoich when you go to touch the gas, the problem is 100% in the transient fueling which is 100% caused by the marine intake. Try the link above to get an idea for how to monkey with the transient tables. Impact factor is the one you want, it's a 3D table that plots various MAP values against ECT. You'll want to increase the delta between the higher MAP cells. Take a look at the histogram. There's about a .25 second delay that you can see with the TPS going up and the AFR subsequently taking a dump. I've had the worst time being scientific about bumping these cells, that's about as close as I can get. Try bumping until that dip goes away. Then you get to figure out how to blend those normal operating temps down to the cold weather stuff. When it gets cold enough, the stumble goes away, comes back, then mostly goes away again as it approaches normal operating temp. You don't get much time on the thing when it's stone cold either.

[THEFERMANATOR]

I forgot on the knock, when I was logging it I seen quite a bit of knock retard(as high as 7 degrees IIRC). I know I have some bad lifters that bleed down below 1500 RPM's and it logs quite a bit of knock going in to lock up(it dropped the timing down to 7 degrees which makes it feel VERY doggy locking up in OD).

[THEFERMANATOR]

I got out this weekend and did the calc.maft method to get a better VE table. I pulled 3-6% out in the 400/800 rpm rows, and 3-4% out from 4000+ from what the calc.vet method generated for a VE table. Unfortunately Florida decided to go back to summer, so I will have to wait for some cooler weather to see how this works out as far as the going lean off idle when cold. I will say the throttle response and driveability is WORLDS better on a 80 degree day than it was with the stock VE table, or even the 1st table I made from the calc.vet method.

[SOMFormula]

I'd have to see your file/stock file/Datalog w/wideband data.
You can compensate for some of that in the VE, some of it in the OL tables. Some of it in the Dynamics Table.
It all depends on the mods/ECU/OS.