lean area around 2500ish rpms-2014 ctsv

[L1FTD]

Will definitely try disabled on every o2 and trim related DTC If that doesn't get Oxygen tests completed, maybe even do every single DTC and let it idle and see how that goes. Beyond that, back to square one.

A minor (or major?) success with the DTC's.

Setting all o2 sensor 1 DTC to 'no error', and all trim DTC to 'no error' has cleared all readiness tests for me.

I haven't driven the car yet. Read DTC's before flash; oxygen sensor + heater incomplete. Flashed tune, read DTC's; all complete, 0 emission DTC.

Might pose a future problem if running closed loop. I'm currently open loop, so will see how it goes when I get a chance to drive.

Also, be good to find which exact codes completed the tests. I just mass disabled for now, but if it only needs a couple, even better.

Screenshot (7).jpg

Screenshot (8).png Screenshot (9).png Screenshot (11).png Screenshot (13).png Screenshot (14).png Screenshot (15).png

[L1FTD]

A minor (or major?) success with the DTC's.

Setting all o2 sensor 1 DTC to 'no error', and all trim DTC to 'no error' has cleared all readiness tests for me.

I haven't driven the car yet. Read DTC's before flash; oxygen sensor + heater incomplete. Flashed tune, read DTC's; all complete, 0 emission DTC.

Might pose a future problem if running closed loop. I'm currently open loop, so will see how it goes when I get a chance to drive.

Also, be good to find which exact codes completed the tests. I just mass disabled for now, but if it only needs a couple, even better.

Screenshot (7).jpg

Screenshot (8).png Screenshot (9).png Screenshot (11).png Screenshot (13).png Screenshot (14).png Screenshot (15).png

A minor success, if any at all. Lucky I'm not holding my breath with this anymore.

Went for a drive with all tests 'complete'. No difference to the lean spots, still the same part-throttle and WOT. Only DTC I had active was P0102 (MAF fail for SD). This appears to come up as an emissions DTC as well, but that's irrelevant since some of you guys are blended air anyway.

For anyone that wants to try, just set all o2 sensor 1 DTC to 'no error' and SES UNchecked (same as sgod1100). Make sure to not leave any SES on, car will start then go max. fuel pump/flow, and stall

No need for the fuel trim DTC's, tests complete without those. Pretty much same as my screenshots, just uncheck the SES, and disregard anything not specifically o2 sensor 1.

My setup is: bank 1 stock, both o2's connected. Bank 2 front o2 connected, rear o2 disconnected and removed for wideband. May have different result if my bank 2 rear was connected?

The o2 seemed more responsive, definitely something going on with bank 2. Looking back through logs, bank 2 o2 always drops further than bank 1. Very clear in this screenshot.

Screenshot (16).png

Screenshot (17).png

[sgod1100]

A minor (or major?) success with the DTC's.

Setting all o2 sensor 1 DTC to 'no error', and all trim DTC to 'no error' has cleared all readiness tests for me.

I haven't driven the car yet. Read DTC's before flash; oxygen sensor + heater incomplete. Flashed tune, read DTC's; all complete, 0 emission DTC.

Might pose a future problem if running closed loop. I'm currently open loop, so will see how it goes when I get a chance to drive.

Also, be good to find which exact codes completed the tests. I just mass disabled for now, but if it only needs a couple, even better.

Screenshot (7).jpg

Screenshot (8).png Screenshot (9).png Screenshot (11).png Screenshot (13).png Screenshot (14).png Screenshot (15).png

So i went out of town for the weekend (about an hour drive)....just got back and read the dtcs...there are none however I'm still getting incomplete for evap and oxygen sensor. I did read what you tested out and even with those "completed" or "Not supported" you are still seeing the lean spot...dammit...lol. So do you know which dtc it was that allowed the evap system to be "not supported?

Emissions.jpg

[sgod1100]

Yeah definitely sounds plausible. Cat test disable might not do anything on the LSA, or certain LSA, who knows. There?s enough stories of mislabeled or redundant tables in HPT, could be the case.

Doubt HPT would be willing to investigate anything emissions based anymore.

who would we need to ask to possibly have them take a look at it?

[L1FTD]

So i went out of town for the weekend (about an hour drive)....just got back and read the dtcs...there are none however I'm still getting incomplete for evap and oxygen sensor. I did read what you tested out and even with those "completed" or "Not supported" you are still seeing the lean spot...dammit...lol. So do you know which dtc it was that allowed the evap system to be "not supported?

Emissions.jpg

Not sure why your evap. wouldn?t come good after a drive, then again mine is ?not supported?. It may need a lot more driving with no tune flashing. Have heard evap. can take quite a few driving cycles to go complete.

If you look at my screenshot 11, I?ve only got one evap. DTC enabled. This is from factory, checked against another stock tune and it was same. Bit strange. The CTSV and ZL1 tunes have all of them enabled. Might be why mine says ?not supported?.

Oxygen sensor and heater can be fixed by disabling all your o2 sensor 1. Not sure how this would effect closed loop, I?ve only tried in open loop. Need someone with all four o2 connected to try this. I?m missing the rear for bank 2, could connect it back, don?t think it will help though.

In the engine diagnostic > exhaust tab, there are pre and post cat o2 thresholds. If someone had all four o2 connected, could try adjusting those values so the ecm thinks it?s constantly lean. If it thinks it?s lean, might not push further lean, maybe go back rich. That?s if the thresholds are there for a test, and if that test is even the reason for our problem?

[sgod1100]

Not sure why your evap. wouldn?t come good after a drive, then again mine is ?not supported?. It may need a lot more driving with no tune flashing. Have heard evap. can take quite a few driving cycles to go complete.

If you look at my screenshot 11, I?ve only got one evap. DTC enabled. This is from factory, checked against another stock tune and it was same. Bit strange. The CTSV and ZL1 tunes have all of them enabled. Might be why mine says ?not supported?.

Oxygen sensor and heater can be fixed by disabling all your o2 sensor 1. Not sure how this would effect closed loop, I?ve only tried in open loop. Need someone with all four o2 connected to try this. I?m missing the rear for bank 2, could connect it back, don?t think it will help though.

In the engine diagnostic > exhaust tab, there are pre and post cat o2 thresholds. If someone had all four o2 connected, could try adjusting those values so the ecm thinks it?s constantly lean. If it thinks it?s lean, might not push further lean, maybe go back rich. That?s if the thresholds are there for a test, and if that test is even the reason for our problem?

I actually adjusted those mV values in the engine diag>exhaust tab for the down stream o2s...i currently have 1mV for "lean threshold" and 1499 mV for rich threshold. Obviously lean spot still there though

[L1FTD]

I actually adjusted those mV values in the engine diag>exhaust tab for the down stream o2s...i currently have 1mV for "lean threshold" and 1499 mV for rich threshold. Obviously lean spot still there though

Yeah I guess that puts it in the middle, I’d think. Anything below 1mV is lean, anything above 1499mV is rich, so ecm always thinks it’s in the middle and good. Other thought I had was making it say 1499 rich and 1498 lean. Makes it think you’re constantly lean so it won’t want to push leaner. Or the other way, 1 lean and 2 rich, always thinks it’s rich. Suspect I might need all four o2 connected, I’m sure there’s a hidden fault for the broken circuit with the rear I removed.

Who knows if it’s even a damn test we’re looking for, wish we knew a direction to go, tune related or 100% a test.

[L1FTD]

who would we need to ask to possibly have them take a look at it?

No idea on that one. I’ve been lurking here for a while, but any issue I had there was always plenty of info from other members who fought/fixed the same thing. This is the only unresolved issue, seems a bit like the desoot mode drama, somethings got to pop up soon.

I see the HPT admins post every now and then, less these days. Give good info on the tables and background things we can’t see. Just can’t imagine they’d want to say anything about this thread, with everyone not running cats and trying to find an emissions test or tune around it

[sgod1100]

No idea on that one. I’ve been lurking here for a while, but any issue I had there was always plenty of info from other members who fought/fixed the same thing. This is the only unresolved issue, seems a bit like the desoot mode drama, somethings got to pop up soon.

I see the HPT admins post every now and then, less these days. Give good info on the tables and background things we can’t see. Just can’t imagine they’d want to say anything about this thread, with everyone not running cats and trying to find an emissions test or tune around it

Yeah, would be great if it was the "desoot" solution. That one was going on for a while and it was just a simple check box...lol. I may try setting those mV to "always lean" to see what happens..won't hurt to see what happens. I've literally looked through the tune hundreds of times, trying to see if I missed something obvious, but I don't think I have unfortunately. I think you mentioned a while ago about everyone having this problem and not noticing it. I've seen multiple guys' logs and while they don't have a WB hooked up every time they go through that 2600 rpm their fuel trims go positive just like ours do. I'm willing to bet more guys are having this problem than we think, but just don't notice it.

[InfraRedline]

Bringing this thread back up since a few of us were talking about it in another thread recently. Not that we have found a solution, but I can confirm that I have seen these same symptoms on my 09 C6 ZR1 as well. I first noticed the lean spots at 1600 and ~2600rpms (this one much more noticeable) when I installed my 1300cc injectors and flexfuel kit on an otherwise completely stock car. I still had my rear o2's in and all codes on initially, but didn't run it in the stock + 1300cc configuration for long. Once I did the ported blower, throttle body, intake, pulley, and intercooler bricks I put my dual widebands in and started trying to dive into a bit while still having a completely stock exhaust, and that is the configuration I did most of my testing on. I started out on MAF and was trying to add humps in the MAF curve to combat it, but quickly switched to SD due to the intake I am running and being able to make the car idle and drive at low speeds much smoother. I tried ramping the fuel pressure from low flow to normal flow mode both earlier and later to try different fuel pressure targets while crossing through the 2600rpm range with no change. I also tried different injector scalings with no change (at one point I didn't half the IFR and just let it max out at 127 lb/hr for the rest of the table just for testing). I've tried playing with the injector flow rate and min pusle width tables in the FPCM with no noticeable change.

I now have headers on the car, and the last time I had it on the dyno I took some time to just sweep through the low rpms at different load ranges to try to dial in the VVE table and work around the lean spots, and ended up with some decent humps in those areas. So while it isn't a pretty or normal looking VE table it does seem to work pretty well and I would say I'm pretty close to happy with it, but ultimately the only way I have made it any better has still just been a workaround by manipluating the VVE rather than finding an actual fix.

[JayRolla]

Seems like this must be either GM designed or a bug in the software. Its more noticeable when we start to mod and untuned because I used to really feel it till I tuned it out as much as possible. I have the same humps in my VVE table, also in the MAF curve and have added a good 8-10% to the PE table around 2500rpms. During CL cruise I get a lean spike to around 1.08-1.14 depending on throttle amount. And at OL/WOT I go from .73 to about .80 before it settles back to my commanded .77. I feel it's the best it's going to get and not going to chase my tail anymore trying to fix this issue. I went through at least 40 flashes trying different stuff and I am over it now. LOL

[sgod1100]

Seems like this must be either GM designed or a bug in the software. Its more noticeable when we start to mod and untuned because I used to really feel it till I tuned it out as much as possible. I have the same humps in my VVE table, also in the MAF curve and have added a good 8-10% to the PE table around 2500rpms. During CL cruise I get a lean spike to around 1.08-1.14 depending on throttle amount. And at OL/WOT I go from .73 to about .80 before it settles back to my commanded .77. I feel it's the best it's going to get and not going to chase my tail anymore trying to fix this issue. I went through at least 40 flashes trying different stuff and I am over it now. LOL

Yeah, i'm probably close to 100 flashes...lmao. I'm to that point as well, just leaving it be unless someone who is smarter than me figures out the root cause/solution.

[PGA2B]

I moved past it as well. Just get it to as good as I can in those areas.

[Cringer]

Has anyone logged the EVAP commanded duty cycle to compare against these lean spots yet?

[sgod1100]

Has anyone logged the EVAP commanded duty cycle to compare against these lean spots yet?

I personally haven't. The only PID I have is "commanded evap purge" ("ratio" units). I have logged if the vent is open and/or close and it stays close through the leans spots from what I remember in the past.

[sgod1100]

Just as an fyi to everyone Jayrolla on here sent a video to me of a mildly modified ctsv. This car has the same issue we are having. Video is here and I took two screen shots of the afr just prior to going into the 2600 rpm area and during. Note the afr between the two screenshots. So this car has the same problem ours does. I'm beginning to think it's much more common than we think. Granted the afr hitting that 13:1 is very quick and goes back down to the commanded of 11.5.

https://www.youtube.com/watch?v=xTK6FakuS1U

2600 rpm.jpg2400 rpm.jpg

[JayRolla]

I also watched another v2 video and then an LSA ZL1. The ZL1 was commanding mid 11 AFR before the spike to high 12's. The CTS was commanding 14'ish under boost at WOT before spiking to 16's. Not once in any of these videos does the dyno tuner mention the spikes and just moves on.

[sgod1100]

I also watched another v2 video and then an LSA ZL1. The ZL1 was commanding mid 11 AFR before the spike to high 12's. The CTS was commanding 14'ish under boost at WOT before spiking to 16's. Not once in any of these videos does the dyno tuner mention the spikes and just moves on.

Wonder why they just ignored that and not said anything

[JayRolla]

Wonder why they just ignored that and not said anything

Probably because yes its under boost, but its low rpm, lower load and onset of PE hitting. Not as dangerous to be slightly lean for a small period of time at low RPM. But the CTS-V was dang lean down low for a long time with 10psi. He is a very well known tuner, usually does about 3-5 hits and is done. This is another reason I like doing my own tuning but I might get a little too OCD over it. LOL.

[L1FTD]

A while back I went through all the dyno sheets posted over on the camaro5 and ctsvowners forums. Just the ones in the 'dyno' threads. Very common, can see the issue on a lot of the cars. Hard to pick, can only see it on the sheets that have AFR graphed. Even then, don't have the tune so can't see if the tuner was throwing extra fuel in. Can definitely see a lot trending lean around the problem RPM though.

The problem seems to go away on bigger HP builds, presumably with aftermarket fuel systems (fuel rails, FPR, FSCM delete etc.).

Doesn't seem to matter what platform. My car (Australian HSV w/ LSA) does it, CTSV does it, Camaro ZL1 does it, even Corvette ZR1 does it (noted by another member).

Attached pics of an intrusive pressure test in the FSCM, and a shot of my pressure spiking at 2600rpm. Could be an anomaly, I don't normally see a spike, but interesting nonetheless.

I think whatever is causing this, is either in the FSCM (intrusive test), or it's fuel pulse/pressure resonance in the factory fuel system.

Fuel pulse/pressure resonance somewhat common on other makes and engines. Threads on other forums for completely different cars, same problem in the same RPM (erratic lean spikes, can't tune out etc.) Fix is always interrupting/altering the fuel system, one way or another.

The fix would be going aftermarket fuel system (upgrading the rails, and using FPR and pulse dampers), and deleting the FSCM. They go hand-in-hand I guess.

If anyone has deleted/bypassed the FSCM, could set any of the codes in the pic I attached, to MIL first error and uncheck SES. That should set a code and disable the FSCM test. I don't think anyone in this thread can, I think we're all running the FSCM and relatively stock fuel systems.

FSCM Pressure Test.png FSCM Pressure Test 2.png FP Spike.png