Fuel tuning

[southern]

Hey guys I am getting a little more into the tune and I have not messed with the pe fueling or much of the fueling for that matter and was kinda wondering should I lower the spark to dial in the fuel and then come back in and start adding timing after I get the fuel leaned out a little? So what all can/do I need to adjust on the fuel.

[SSpdDmon]

A few details on the truck would be helpful. Is it stock, bolt-ons, cam'd, etc.?

[southern]

guess that would help huh. By the way it has been kinda running a little lean since the header install, Here is a log from this morning.
04 GMC 1500
5.3L
Headers w/ custom exhaust
intake
PLX Wideband

[SSpdDmon]

Well, it looks like you upped the spark on the tune....perhaps too much since you're getting knock retard. I don't know why you would think the truck is running lean though. The fuel trims are negative - meaning they're pulling fuel at part throttle - and you're AFR is between 11:1~12:1 at WOT. The truck is running a little rich. I'd try leaning out the PE table so that you hit ~12.5:1 at WOT across the board. Also, I'd put the timing back to stock until you can get on a dyno to find out if more timing is making more power.

[southern]

look at the part throttle AFR it kinda gets lean every now and then I thought. Timing was good but I got some cheap gas last time I got gas by mistake but I need to lower it in order to lean it out right? Cause I was getting more knock when I leaned it out the other day. But I will lower it a try the whole fuel thing then go back to the timing. You said change the AFR in the PE table you talking about the B3618 table?

[5.7ute]

You are not hitting PE mode & commanding too lean a mixture in the high load areas. Do as SSpdDmon has suggested & change your pe table to a flat 12.5 & return your timing to stock. Lower your PE throttle position enablers so it can enter PE mode easier. Might also help to richen up your B3605 table in the high map areas as well. Running a stoich mix at 100kpa will knock.

[SSpdDmon]

You are not hitting PE mode & commanding too lean a mixture in the high load areas. Do as SSpdDmon has suggested & change your pe table to a flat 12.5 & return your timing to stock. Lower your PE throttle position enablers so it can enter PE mode easier. Might also help to richen up your B3605 table in the high map areas as well. Running a stoich mix at 100kpa will knock.
IIRC, he had dropped his PE TPS Enable table. But, it still looked a little high. You might want to drop it another 15~20, southern.

If PE comes on easier, it shouldn't matter if he's commanding stoich in B3605 because PE should override it.

As for the AFR leaning out a little every now and then southern, that's a normal part of closed loop (part throttle). The long term fuel trims learn based on the behaviors of the short term fuel trims. The STFT's swing the AFR above and below stoich to generate an average. If the average AFR swings are greater than stoich, the LTFT's will increase to move the average back down closer to stoich. The opposite happens if the average swings are less than stoich. As long as your NBO2 sensors are working alright, part throttle should be fine. Try to get the fuel trims close to zero just before tuning WOT though. That way, if the AFR leans out, the positive fuel trims will be added to WOT to compensate. If the LTFT's are too negative, you lose that safety net of having the PCM learn over time. This is because negative fuel trims don't affect WOT - only positive LTFT's do. In other words, if you tune when you have -10% fuel trims, then the car has to lean out 10% before it'll start to learn to add more fuel at WOT. Assuming you tune to a 12.5:1 AFR, that means you could potentially lean out to 13.8:1 AFR (10%) before positive fuel trims would start adding fuel back in.

[5.7ute]

If PE comes on easier, it shouldn't matter if he's commanding stoich in B3605 because PE should override it.


I agree 100%. I just like to richen up the high map areas as a safety net.

[SSpdDmon]

I made a few changes based on past experiences with f-bodies. I realize the truck is a little different, but the concepts should be parallel.

Since it's just a bolt-ons setup, your fueling shouldn't be off by more than 5~6%. So, I adjusted the VE and MAF accordingly to give you a good base to work from. The 15% mentioned in the tutorial is a bit overkill for N.A. applications. This change should help bring your fuel trims closer to zero, which is a good thing.

PE is set to 12.5:1, so the truck should feel stronger than it used to with that change alone.

I pulled a little timing and re-mapped your high/low octane as well as the mixture spark tables. You should see ~27* just before peak torque, ~26* at peak torque, and ~27* after peak torque. Until you can get on a dyno to see if additional spark is making more power, I wouldn't run much more timing than this. On the other hand, you'll have to keep an eye out for knock retard. The table is a bit aggressive, but shouldn't be commanding more timing than what I saw in your log.

Give it a shot (for a couple of drive cycles so the fuel trims can learn) and let me know how it does...

:)

[southern]

thanks guys I will give that a try and mess with my tune a little as well.

[southern]

hey how long should it take for the ltft so settle back down, cause they are ~-5 to -12 after that tune and they were around -3 to -8. Do I just need to redo my auto VE and try to get them back in shape? But on a good note it is running smoother and better now.

[SSpdDmon]

Did you reset the fuel trims after you flashed it? Sometimes, they don't reset.

If so, I'd give it a couple of drive cycles to see how it does. If the EVAP system kicks in, the fuel trims will take a dive for a short while. If the fuel trims don't get back closer to zero after a couple of trips, try putting the stock MAF curve back into my tune and see how it does.

How did WOT look/feel? AFR? Knock retard?

The VE you had didn't look like you made it through the AutoVE process. Most of the table was jacked up 15%, which doesn't seem right for just bolt-ons. If you want to spend the time on re-mapping the VE, go for it. But, I wouldn't bother with stock internals. The bumps I made should help with transitions. Steady airflow fueling calculations are still done with the MAF. So, if you see consistent errors in fuel across a certain MAF Hz range, I'd make some small adjustments to that part of the MAF curve to bring things back in line.

[southern]

ya the VE table I was working on up to around 35-4000rpm and had my fuel trims with in 0- -4 and the logged ve to .98-.102. I did not reset the fuel trips, and I am not sure about the Evap. WOT was good it felt a little stronger the little chance I got wot. I had around 3* of knock at part throttle a time or two but nothing real bad.

[SSpdDmon]

ya the VE table I was working on up to around 35-4000rpm and had my fuel trims with in 0- -4 and the logged ve to .98-.102. I did not reset the fuel trips, and I am not sure about the Evap. WOT was good it felt a little stronger the little chance I got wot. I had around 3* of knock at part throttle a time or two but nothing real bad.
If that KR is consistently there at that point in part throttle, you may want to pull some timing in that region.

[cmitchell17]

Where is the KR?

Is it when the TC is locked at low rpms high airmass?

I had to take thoes cells almost back to stock. After thinking about it the stock tables should be almost optimal at the non WOT levels. I havent changed my timing in a long time, but I got it to where it will advance to about 28-29 degrees at 3400-3600rpm then back down to about 26.5-27 then back up to 28-30.

[southern]

man I cant remember where the kr was I have went back to an old tune for the fuel mileage since I have been about 3k miles in the past 2 weeks. But I am running 89 octane and I was just seeing a little in a spot or two.

[cmitchell17]

Yeah I noticed some last night at WOT so I dropped .5 degrees about 4600.

[dsmlights]

this is a good thread i learned quite a bit :) now I know why people do auto VE to keep the LTFT to 0 .