Leans way out at idle, way rich on throttle, VE table looks rediculous

[AdsoYo]

There are so many issues, I feel like I must be missing something fundamental. I've spent the weekend attempting to tune my LS3 swapped '94 TransAm. It's a crate LS3 with a 216/226-116+3 cam. I have an AFR500 wideband and hptuners. Up until this weekend I was using a stock 2002 TransAm file with my old MAF table from the LT1, the spark table from an LS3, and fuel tables for the LS3's 39# injectors. For both VE and MAF tuning I turn off LTFT's, closed loop, and power enrichment. I have the same issues with both MAF and speed density modes.

First problem is the car runs lean in general after a warm start. It runs lean for a few minutes before snapping out of it. I've found other threads on the issue but no resolution. After a few minutes of driving I can finally start recording data.

Even after dialing in idle it will still lean out. For instance I could come to a stop and idle will settle to 14.x but after a few seconds it pegs at 16+. I have to adjust it way rich to prevent this from happening. In closed loop it will lean way out, then the PCM adjusts the fuel to bring it back to stoich, then after a few seconds it goes way rich and gets adjusted back the other way again.

When tuning MAF, if I got in the throttle to hit the higher cells it would lean way out then after a few seconds it would peg itself max rich, like 9.0/1. I feel like I must be missing a table somewhere that's affecting my fueling. This only happened at 5,000hz and up.

My VE table looks like no other table I've seen. Looks like it has a growth on the front and a huge chunk missing in the back. It is the culmination of hours of driving and applying data though. I was facing similar issues where one minute a cell would read one AFR and if I were to revisit the cell later it might read a totally different AFR. Made tuning very frustrating.vetable.jpg

[SiriusC1024]

LT1 MAF? Like the mid-90's fbody LT1?

What sensors did you change on the LS3? MAP sensor, for example.

[AdsoYo]

I'm using an LS1 MAP, MAF, O2 sensors, 0411 PCM with lingenfelter box

[blindsquirrel]

Even after dialing in idle it will still lean out. For instance I could come to a stop and idle will settle to 14.x but after a few seconds it pegs at 16+.

Catalyst and/or post-O2 tests are trying to run over and over, because you have no cats and have, I assume from looking at the file, totally removed the rear O2s. These tests can't be disabled in the Gen3 PCM. When it can't get a result from the test it keeps trying again and again anytime the conditions are met (one test runs at idle, other test runs while driving in a window of certain conditions).

If the tests are able to run and fail, they will stay failed and it will stop running the tests until it thinks the problem has been repaired (or codes cleared - even though it does not set codes when P0420/P0430 are disabled).

The solution is to plug some rear O2s back in, something most people really do not like to hear because they already chopped all that wiring out of their super-slick custom reworked harness and threw it away.

You can't tune around this. As you found if you try to make it richer while it's intentionally commanding it lean for the tests, it's too rich when the tests stop. And you can't force it to not run those tests other than by letting it run them and then fail, and it can't do that if there are no rear O2s plugged in.

Description of how this all works doesn't exist in the service manual since these tests do not have their own DTCs and aren't part of the other cat/rear O2 codes that have been disabled. But from the description for P0420/P0430:

- The PCM captures the current rear HO2S rich-to-lean status.
- The Air/Fuel ratio transitions from rich to lean, or from lean to rich, depending on the capture rear HO2S rich-to-lean status.
- The Air/Fuel ratio transitions a second time opposite the first Air/Fuel ratio transition.
- The PCM captures the response time of the front and rear heated oxygen sensors when the Air/Fuel ratio transitions occurred. The response time is the time during which the HO2S goes from below 300 mV to above 600 mV, and from 600 mV to below 300 mV.
- The PCM measures the time for the rear HO2S voltage to cross a reference rich-to-lean threshold, minus the time for the front HO2S voltage to cross the same rich-to-lean threshold. The time difference from the front and rear HO2S is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.

[SiriusC1024]

Unrelated to your issue, but LS3 coils? If so, you need to adjust dwell so they don't burn up.

What about TB?

IAT, ECT...is it all LS1 parts?

[AdsoYo]

Catalyst and/or post-O2 tests are trying to run over and over, because you have no cats and have, I assume from looking at the file, totally removed the rear O2s. These tests can't be disabled in the Gen3 PCM. When it can't get a result from the test it keeps trying again and again anytime the conditions are met (one test runs at idle, other test runs while driving in a window of certain conditions).

If the tests are able to run and fail, they will stay failed and it will stop running the tests until it thinks the problem has been repaired (or codes cleared - even though it does not set codes when P0420/P0430 are disabled).

The solution is to plug some rear O2s back in, something most people really do not like to hear because they already chopped all that wiring out of their super-slick custom reworked harness and threw it away.

You can't tune around this. As you found if you try to make it richer while it's intentionally commanding it lean for the tests, it's too rich when the tests stop. And you can't force it to not run those tests other than by letting it run them and then fail, and it can't do that if there are no rear O2s plugged in.

Description of how this all works doesn't exist in the service manual since these tests do not have their own DTCs and aren't part of the other cat/rear O2 codes that have been disabled. But from the description for P0420/P0430:

Thank you for that explanation! I knew there had to be something. I still have a question though. I did the 24x conversion on my old LT1 in 2014 and have been running this exact PCM ever since then. (24x conversion involves removing the optispark distributor and installing coil packs, crank and cam sensors, and the LS1 PCM for those unfamiliar. The more popular option these days is the Torqhead 24x kit) That setup didn't have rear O2's either but I never faced this situation. Tuning was predictable. Something must be different now.

Unrelated to your issue, but LS3 coils? If so, you need to adjust dwell so they don't burn up.

What about TB?

IAT, ECT...is it all LS1 parts?

Yes LS3 coils, do you know what the dwell should be? TB is a Nick Williams 92mm, all sensors except for crank position are LS1. The coolant temp sensor was a weird one, I HAD to use a 98 fbody sensor with 3 wires to feed both the PCM and my dash gauge.

[SiriusC1024]

Pull the dwell info from an LS3 file.

[SiriusC1024]

Tune is super rich, especially in the VE tuning log. Commanded seems ok, but the actual is what's telling.

Why are you running open loop in the logs? Fuel trims aren't working at all.

Obviously, VE is way exaggerated. How exactly did you go about doing your VE tuning?

[AdsoYo]

Tune is super rich, especially in the VE tuning log. Commanded seems ok, but the actual is what's telling.

Why are you running open loop in the logs? Fuel trims aren't working at all.

Obviously, VE is way exaggerated. How exactly did you go about doing your VE tuning?

Yes the point is to eliminate fuel trims when tuning the MAF and VE. Turn off trims, turn off power enrichment, find an empty country road or highway and start hitting all the cells. I used mostly 5th and 6th gears, holding the throttle at certain points to hit each cell in the table. For instance when filling the 2000 rpm column, I would hold the throttle at 5%, barely cracked open, to hit the 30 kpa cell for that column. Then I would let off and slow down and push the throttle to 10% to hit the 40 kpa cell and so on. Very tedious and time consuming. Now that I know I was working against some phantom feature of the PCM this whole time, this whole weekend feels like a waste. I don't even want to think what all that driving in extreme lean and rich conditions did to the engine.

So were the "real" numbers the rich ones then? Or does the PCM intentionally command super rich as well as lean when it does these tests? And why do these tests trump everything else affecting AFR? Seems like some real damage could occur running so far off 14.7 for the sake of testing the O2 sensors.

[SiriusC1024]

No you leave STFT on. Turning off LTFT is optional. Some use it, some don't. You need STFT at least to find how far off fueling is to then correct the VE table.

Right now PCM is using the open loop table to inform fueling. It's trying to hold that value in relation to the VE table. Since VE is too high, fuel is rich.

What have you been basing your changes to VE on?

[blindsquirrel]

No you leave STFT on. Turning off LTFT is optional. Some use it, some don't. You need STFT at least to find how far off fueling is to then correct the VE table.

Right now PCM is using the open loop table to inform fueling. It's trying to hold that value in relation to the VE table. Since VE is too high, fuel is rich.

What have you been basing your changes to VE on?

screenshot.15-05-2023 02.24.16.png

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I do notice that you're still logging Mass Airflow & MAF Hz in this 'vetuning' log. Should not do that. Make separate channel lists for VE tuning and MAF tuning if you have to.

No Cylinder Airmass? No TPS?? No Injector B1/B2 ms? No P0102/P0103 in the log, was one of those 'Current' when it was supposedly in speed density?

[AdsoYo]

No you leave STFT on. Turning off LTFT is optional. Some use it, some don't. You need STFT at least to find how far off fueling is to then correct the VE table.

Right now PCM is using the open loop table to inform fueling. It's trying to hold that value in relation to the VE table. Since VE is too high, fuel is rich.

What have you been basing your changes to VE on?

I think see what you're saying. I'm using my wideband for that purpose. I have a table in the scanner that records the AFR error and I copy/paste multiply by % half over and over until it's within 4%.

[blindsquirrel]

Please don't turn off PE & DFCO and all the rest. Leave it as-is, and remove the stuff you don't want affecting your data with filters. And besides, actual vs commanded error is actual vs commanded error whether it's commanding 14.69 or 12 or 13.1 or whatever. That's the whole point of using a wideband to do all areas of the map.

[AdsoYo]

screenshot.15-05-2023 02.24.16.png

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I do notice that you're still logging Mass Airflow & MAF Hz in this 'vetuning' log. Should not do that. Make separate channel lists for VE tuning and MAF tuning if you have to.

No Cylinder Airmass? No TPS?? No Injector B1/B2 ms? No P0102/P0103 in the log, was one of those 'Current' when it was supposedly in speed density?

Ah, setting the MAF fail frequency lower is a step I forgot. I was thinking since I set the high RPM disable to 9999 the MAF was out of the equation. Like I said, haven't done this in years. I didn't change my scanner settings between MAF and VE because I wouldn't be able to use the additional info with my limited knowledge. All I want is the MAF and VE AFR error tables.

Can you think of any reason these fuel issues weren't happening with my LT1 but now they are? I believe you about the rear O2 testing but there must be some reason it wasn't happening before.

[SiriusC1024]

I think see what you're saying. I'm using my wideband for that purpose. I have a table in the scanner that records the AFR error and I copy/paste multiply by % half over and over until it's within 4%.

How's it so far off then? It's like a good LS3 approximation was derived from a VVE to VE conversion then corrections were applied that skewed it massively.

[blindsquirrel]

Did you confirm, by some fashion, that you had a P0103, which is needed before you can say 'yup, it's in SD'? Just because it doesn't show up in the log's 'Details' tab isn't a reason to say it wasn't set, sometimes they don't if it's the first run cycle after a reflash even though it's there if you read DTCs with the 'Diagnostics and Info' button. Just asking if you checked. If you did, and it was, then fine. If you didn't and don't know if it was or wasn't, maybe think about starting over.

There's all kinds of cool shit you could be logging. Like MAF Status: Fail/No Fail, for just one tiny one. I know you don't want to mess with anything you don't see as directly related to the one specific thing you're trying to do, but there is stuff that will help you do that one specific thing if you just spend some time looking through what channels are available to you. I don't know how to read a log without TPS, for instance. It feels like wandering around a dark room wearing a blindfold and earplugs and big puffy mittens.

[SiriusC1024]

I'd be interested in your Scanner config. Do you have one to share?

Also, what's the reasoning for leaving DFCO on? I can understand PE left on given this method (new to me) of doing the VE table with a wideband. Is an AFR commanded during DFCO?

[blindsquirrel]

If you log the DFCO flag you can simply add a filter that doesn't add error data to your Graph when DFCO isn't 'no'. Like everything else for something to be used in a Graph (or, a filter) it has to be in the main channels list.

[SiriusC1024]

Wouldn't that prevent a few cells from populating though? Like the higher rpm, low MAP zones?

I guess it wouldn't matter if working under the assumption that DFCO thresholds wouldn't be changed. It could be a problem if they were to be changed at some point and respective VE changes were neglected there.

[Alvin]

That VE table doesn't look correct at all.

Just to be on the same page.. you fail the maf by unplugging or setting the diagnostics low were it will fail, see that a 101,102, 103 code is active so you know it is in speed density, then tune the VE tables

Correct?

This looks like you've been making VE changes with the MAF active