Fuel trims climb then return to normal during driving

2016 Camaro SS M6: TSP LTs with no cat x, MSD intake, 103 TB, Rotofab dry, flex fuel sensor

I'm mainly just tweaking small things here while learning gen V tuning. Thought I'd mess around with idle and part throttle driving for now.

Dialed in idle areas of MAF and VVE using WB error, then smoothed into existing values prior to this drive. Most of the drive was uneventful and on dash WB looked good during the drive. First time I noticed something amiss was at a stop near the end of the drive. After exiting DFCO, WB stayed WAY lean at idle and kept trending more lean. Tried applying a little throttle and WB moved back toward the rich direction hoping to prevent any damage. No issue as long as the car was under throttle. Got it home and started looking through the log.

I see lots of areas where LT and ST trims keep trending leaner then return to near zero. Apparently the ECM was able to add enough fuel during those events that the WB showed everything was in check... until it couldn't keep up and it wasn't. Any suggestions on what would cause trims to skew like they did, especially when the car returns to idle?

Before VVE:
Attachment 127528

After VVE showing how little was changed:
Attachment 127529

MAF deltas:
Attachment 127530

Tune and log:
Attachment 127531
Attachment 127532

Quote:

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Originally Posted by liviner

2016 Camaro SS M6: TSP LTs with no cat x, MSD intake, 103 TB, Rotofab dry, flex fuel sensor

I'm mainly just tweaking small things here while learning gen V tuning. Thought I'd mess around with idle and part throttle driving for now.

Dialed in idle areas of MAF and VVE using WB error, then smoothed into existing values prior to this drive. Most of the drive was uneventful and on dash WB looked good during the drive. First time I noticed something amiss was at a stop near the end of the drive. After exiting DFCO, WB stayed WAY lean at idle and kept trending more lean. Tried applying a little throttle and WB moved back toward the rich direction hoping to prevent any damage. No issue as long as the car was under throttle. Got it home and started looking through the log.

I see lots of areas where LT and ST trims keep trending leaner then return to near zero. Apparently the ECM was able to add enough fuel during those events that the WB showed everything was in check... until it couldn't keep up and it wasn't. Any suggestions on what would cause trims to skew like they did, especially when the car returns to idle?

Before VVE:
Attachment 127528

After VVE showing how little was changed:
Attachment 127529

MAF deltas:
Attachment 127530

Tune and log:
Attachment 127531
Attachment 127532

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I'm just wondering did you make your fuel changes for idle when it was completely warmed up?

Quote:

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Originally Posted by liviner

2016 Camaro SS M6: TSP LTs with no cat x, MSD intake, 103 TB, Rotofab dry, flex fuel sensor

I'm mainly just tweaking small things here while learning gen V tuning. Thought I'd mess around with idle and part throttle driving for now.

Dialed in idle areas of MAF and VVE using WB error, then smoothed into existing values prior to this drive. Most of the drive was uneventful and on dash WB looked good during the drive. First time I noticed something amiss was at a stop near the end of the drive. After exiting DFCO, WB stayed WAY lean at idle and kept trending more lean. Tried applying a little throttle and WB moved back toward the rich direction hoping to prevent any damage. No issue as long as the car was under throttle. Got it home and started looking through the log.

I see lots of areas where LT and ST trims keep trending leaner then return to near zero. Apparently the ECM was able to add enough fuel during those events that the WB showed everything was in check... until it couldn't keep up and it wasn't. Any suggestions on what would cause trims to skew like they did, especially when the car returns to idle?

Before VVE:
Attachment 127528

After VVE showing how little was changed:
Attachment 127529

MAF deltas:
Attachment 127530

Tune and log:
Attachment 127531
Attachment 127532

---

So the best advice I received when tuning my 2018 Camaro with similar mods was to put VVE back to stock. I was doing the same thing as you and it was not needed unless you have a cam. Put VVE to stock and tune MAF above 4k and that's it. Changing VVE at lower rpm really screws with torque management fuel trims. Plus widebands aren't super accurate at idle/low flow. When I did this my car drove way better and fuel trims fell in line.

Quote:

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Originally Posted by kenand1988

I'm just wondering did you make your fuel changes for idle when it was completely warmed up?

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Yep. Coolant and oil temp were in normal operating range.

The Camaro uses the Manifold Switch Open VVE table. Not sure if you noticed you were showing the Closed Switch table.


Also, the Fuel Trims, that behavior is normal as long as it is only on the first or second drive after a flash. I see it on the first or second flash of a tune because the ECU is going through the O2 readiness checks and will send the fuel trims way negative for a little while at idle. These trims are not typically learned long term and it won't hurt the motor at idle. There is no danger there. Also, the exact same thing can/will happen when you change the Ethanol content beyond a certain percentage. So if you were re-fueling and the E content changed, even by a few %, this will trigger the ECU to go way negative in the fuel trims while it tries to determine if the O2 sensors scalar match the reported ethanol percentage by the flex fuel sensor. Lambda 1 is the same for all fuels, the ECU but the ECU can detect that stoich has changed and it tests with the O2's to figure out where to set the new stoich ratio.

If you monitor Ethanol Content and Alcohol Content with VCM scanner, you will see those two numbers don't match after initially changing the ethanol in the tank. The flex fuel sensor reports the updated % in real time but it takes a little time for the other PID to update to match.


Also, with your mods, there is no need to alter VVE much if any at all. Your best bet is to put VVE back to stock, you could add maybe 3-5% across all areas from 2000 rpm down, then blend to 2400 rpm and don't change anything above that RPM. Then change your manifold volume by adding 5-10% to handle the transient fueling. The best way is to increase the MAF smoothly, increase manifold volume by a little bit, and then update the O2 sensor response time due to the headers which will help keep fuel trims in check.


These GEn V's are no cake walk. There is a lot to consider. But they also are very capable of self adjusting with minor mods and there is no reason to get too extreme with your changes for minor mods.

Quote:

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Originally Posted by TriPinTaZ

The Camaro uses the Manifold Switch Open VVE table. Not sure if you noticed you were showing the Closed Switch table.

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Closed and open were updated to the same.

Quote:

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Originally Posted by TriPinTaZ

Also, the Fuel Trims, that behavior is normal as long as it is only on the first or second drive after a flash. I see it on the first or second flash of a tune because the ECU is going through the O2 readiness checks and will send the fuel trims way negative for a little while at idle.

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In this case, trims went extremely positive. I wouldn't think it would command such a lean condition. Ethanol content has been consistent. Haven't put E in it for a couple tank fulls, and it's monitored in the log.

Quote:

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Originally Posted by liviner

Closed and open were updated to the same.



In this case, trims went extremely positive. I wouldn't think it would command such a lean condition. Ethanol content has been consistent. Haven't put E in it for a couple tank fulls, and it's monitored in the log.

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If trims go extremely positive then it is correcting for a lean condition and not commanding a lean condition.

Just from what you're describing and the mods I'm going to say you might want to check O2 settings and cat settings. This will cause all sorts of miss torque calcs and fueling issues just on their own... Just what I would recommend checking if you've not done anything for them yet.

Here's some O2 settings for you to try. Although you did make some adjustments for their new locations this should help a little more.

I'm going to also highly recommend you go back to a stock VVE table for one reason and one reason only - I don't believe you tuned it in right just looking at it. Nothing wrong, just don't believe you considered the fact that the cam is moving and these utilize variable cam timing into the VVE maps. The only way to correctly tune in the VVE table is to lock the cam into a fixed 0 position in the tune and then tune the VVE table. You'll find it changes a decent amount especially in the decel zones when done correctly and honestly with those mods, yes it'll be different, but 15% different which the OE leaves them about 10% loose to need tuning - well I don't know.... You did get all of the cat settings fixed, so good there.

Quote:

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Originally Posted by GHuggins

I'm going to also highly recommend you go back to a stock VVE table for one reason and one reason only - I don't believe you tuned it in right just looking at it. Nothing wrong, just don't believe you considered the fact that the cam is moving and these utilize variable cam timing into the VVE maps. The only way to correctly tune in the VVE table is to lock the cam into a fixed 0 position in the tune and then tune the VVE table. You'll find it changes a decent amount especially in the decel zones when done correctly and honestly with those mods, yes it'll be different, but 15% different which the OE leaves them about 10% loose to need tuning - well I don't know.... You did get all of the cat settings fixed, so good there.

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Starting point for that VVE table was the one given to me by my original tuner. Was always sus about it as it was much different than stock.

Went back to stock VVE. Something I learned just scrolling through things with the VVE is that the RPM boundaries cannot really be adjusted on this platform. Apparently the VVE calculations expect the stock upper RPM zone to start at 3250. It really throws off the shape of the VVE at larger intake cam angles if the zone boundary moves any higher than stock. And before anyone gets alarmed, I didn't load zone boundary changes, just played with them to see what happened with the VVE table/graph.

You can change the zone boundaries. Just takes some careful work. Usually not recommended unless you have pretty extreme airmass changes.

Ok, finally got a log showing the idle issue mentioned above. Rolling idle seems fine, but once stopped it continues to add more fuel to maintain idle. Trims get pretty much maxed out. Tune file used to generate the log also included; MAF was dialed in using STFTs.

Attachment 127798
Attachment 127799

You don't have valve cover breathers or something like that do you? Everything including cylinder airmass in that log is screaming vacuum leak.... Purge valve unhooked, but not corked?

Nothing unhooked that I could see on a cursory check. No breathers. Only thing I can thing of is pinch bolts on the MSD. Will check and retorque them later today and try again.

Quick check of the MSD pinch bolts revealed most of the outer ones 1/4 turn loose. Re-torqued and will take for a drive shortly and get another log. Probably need to revisit MAF ST trims.

You might even want to smoke check it as anything on these causing any sort of a vacuum leak wreaks havoc on them. I've even had rolled intake rubber boots cause enough of a leak to skew things where they were still up on the TB's - just not fully seated...

Quote:

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Originally Posted by liviner

Quick check of the MSD pinch bolts revealed most of the outer ones 1/4 turn loose. Re-torqued and will take for a drive shortly and get another log. Probably need to revisit MAF ST trims.

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curious to see if this was the issue.