08 Z06 LS7 big cam and low rpm light throttle surging - maybe mechanical issue??

[[email protected]]

Cold air intake, long tubes, corsa exhaust. don't know all the cam specs, but about 620 lift both sides.

zero problems except for this surge. wanted to keep smoothing on but massage the tables all i want and not helping much. disable and a big help. but really touchy. so i put timing from 1-2000 to 30 degrees. better. now it's something you notice but could probably live with considering the limited range of it, but still, i don't think it should be there.

similar posts have also zeroed in on closed loop correction and this is choppy and when i just plain turn it off, it is a little better. this is a maf only tune and i don't know the brand of the cold air intake but it's not in the stock housing. i think i have the maf pretty well dialed though.

attached is a log with CL enabled (around frame 540 is where it goes steady throttle and the surging starts) and then later with CL off (around frame 1375). just watch for the "Advance" white line in 3rd one down of chart display to go ruler flat.

so here's what i'm seeing. you look at that advance and it's rock solid. look at etc and it's solid, look at the pedal and solid as well. trims are kinda jaggy though. you can feel the surges here. another try with CL off and it is better, those trims may have been problematic.

but then i look at the o2 sensor readings in the 4th chart display and i see how they have these same tiny dips in them, small but noticeable, just like the surging. what i'm wondering is if there's a mechanical problem. the sensors look like they're recording misfires. perhaps this is a mechanical issue then. stock injectors, stock TB and intake manifold though.

any help on this very much appreciated. would like there to be no surge.

[Jeffrey110]

Large cam, and slight bucking and surging is not abnormal. Timing down low helped mine, but its still there. Parking lot speeds and lower I feel it the most. Maybe 1800 to 2200 rpms. I am sure others with better tuning experience will chime in, sorry I cant help more.

[Eaglegoat]

Air, fuel, timing. Every setup is different. I like to get fueling close, then air, then timing. Once I think I'm done I go back and verify/confirm everything again. It can be very time consuming, but that's what it takes to tame big cams.

[[email protected]]

you really gotta look at in the chart display, especially the later part where i have CL off. advance doesn't change at ALL, fuel by .1ms, maf by no more than 100hz, and then look at the voltage values on the o2 sensors. all those little blips. perhaps the tune is fine and those are misfires. and if that's possible, what's causing that? you really gotta look at it in the chart display portion of the scanner to see this.o2.jpg

[Eaglegoat]

From your o2 voltage I'd say you're rich. Try removing some fuel.

[schpenxel]

Following the misfire thought--have you tried logging some of the misfire count PID's to see if you get anything?

[SultanHassanMasTuning]

did you adjust your EOIT?

[[email protected]]

i need to get car back and see if misfire gives a specific result or something not quite helpful like p0300. the cam was large enough i just disabled the misfire monitor so i'll put that back hopefully something useful.

i don't understand how end of injector timing might affect this. was in another thread but didn't bring any results. and what do you affect? the main table (it's all at 520) or the adder tables?

[schpenxel]

Injection timing being wrong for a particular cam can do some weird things.

Easiest thing (IMO) to change is the boundary table.

Try adding 20 to the whole table and see if it makes any difference, good or bad. Total stab in the dark so don't be surprised if it doesn't help, lol

[Michael_D]

I've been fighting the same thing on my 08Z. Started a thread on it last year, and got numerous helpful tips and suggestions. You might want to comb through that thread and see if anything might help.

At the end of the day though, reversion induced missfires/stumbles/coughs can only be tamed down, not eliminated. And it does not help matters that the 08 vette E38 is missing a couple O2 tables that could help.

http://www.hptuners.com/forum/showth...99m-desperate)

[[email protected]]

THAT was a lot to read. and a lot to do on your part.
car was supposed to be back today to try injector timing table, but was a no show.
i'm sure it'll be back though.
are these the o2 tables GH was wanting?o2 tables.jpg

[barum]

Sorry to bring back an old thread, but I would like to get a confirmation whether this "certain 3rd party tuning software" is really able to give access to the integrator delay parameters in 2006-2008 E38 ecm's HPT is not.

The above post is the second reference this particular topic, the first was made by mourat: http://www.hptuners.com/forum/showth...l=1#post388994

He never replied the question regarding the car/year model/pcm from which the parameters were taken.

Caenews, from which car/model year is this screen capture from?

are these the o2 tables GH was wanting?o2 tables.jpg

If it's from a 2006-2008 E38 I'm starting to seriously consider getting that other software to be able to modify those CL integrator parameters.

Yes, I've read the tables aren't there but something has to be. It could be hard coded but some sort of delay has to be used in this kind of control loop for it to function properly. If this is the case maybe HPT could multiply that value by 1.25..1.4 or so in the custom OS versions as most if not all using custom OS's have LT headers installed anyway.

[[email protected]]

it's from the corvette mentioned. so if it had an e38, then yes, those are editable parameters. if that applies to other cars, i don't know

[barum]

Thank You, Sir.

Yes, it has an E38:



and HPT shows only very limited parameters:



versus "3rd party product":



I find it somewhat strange that we are being said "stop complaining, they are not there" instead of taking it on the long list of work to be done as it clearly can be done.

Yes, I do understand all the needs would have to be prioritized just like in any business, but this is a major factor affecting the every day usability of cammed + LT header equipped cars (pretty much every car here).

[[email protected]]

well i can tell you it didn't help the car i was working on.
try downloading the newest software, they update nearly every day on the latest version.

[barum]

Yeah, there are a lot of things to massage, I've lost count after 300 versions while testing the effect of different parameter combinations regarding the surging/bucking at low rpm & load. It has been much improved but it's better still in OL. Yes, I know some effects of the stg3 cam cannot tamed out.
Running in SD now, but would like use hybrid as it has a better tolerance against climate variations. However, MAF signal quality with MF108 is clearly worse than with OEM MAF location. Will probably try air flow straightener and possibly this as well.

For the record, I just measured the average distance between OEM LS7 exhaust header inlet port and 1st lambda, ~ 13-14". With ARH headers (both 1 7/8" and 2" have the same primary lengths") its ~ 30".

As I've written earlier, the only repeatable effect I have been able to achieve with present 2006-2008 CL parameters is a change in lambda oscillation frequency. I just finished a 500 km run after latest changes, but haven't had a change to take a log, but it felt the best so far.
I lowered the CL proportional limits at low (up to 24 g/s) MAF readings to a very low level in order to limit the oscillation amplitude but I will have to see if it had any visible effect.

[Michael_D]

I installed a straightener. Didn't make any noticeable improvement. Spending a lot of time with VE as well as MAF cal helped the most, with trim error under 2%. My LTFT from bank to bank difference between 1500 - 2000 is still around~5. Difference drops to less than~2 everywhere else. I am pretty convinced that additional O2 control will help. Might have move to the 2010 or newer ECM and tuning tables. I am waiting to hear from S?bast on that.

[jsllc]

Not enough timing in idle table. Yours is 13 with large transitions from idle to normal. should look at 20s. I would start with 20 and blend it in to the rest of the table. Here is a ZL1 with a larger cam. Idles well at 675-700. I run 700.

[barum]

I installed a straightener. Didn't make any noticeable improvement. Spending a lot of time with VE as well as MAF cal helped the most, with trim error under 2%. My LTFT from bank to bank difference between 1500 - 2000 is still around~5. Difference drops to less than~2 everywhere else. I am pretty convinced that additional O2 control will help. Might have move to the 2010 or newer ECM and tuning tables. I am waiting to hear from S?bast on that.

Michael_D, you probably have logs before and after the straightener was installed? I remember you writing you had to calibrate the MAF all over again with substantial changes. So it did have an effect, but not on surging. How close the honeycomb was to the MAF?

Yes, I too have a difference between banks at low rpm, 3-4%, bank2 needing more fuel. I did experiment with LTFT having "fully populated" rpm/MAP-grid in use but went to 2009 C6Z configuration, which results having effectively only two (MAP-based) cells.

I have played extensively with EOIT having made my own calculator simulating the angle at with the fuel enters the combustion chamber. At the moment I've been trying to get fuel spent to be as low as possible, ie. to optimize EOIT over the lower (< 2500 rpm) range for efficient burning.
I looked at your resultant EOIT and having tested with similar I only ended up wasting fuel. I log pulse widths from both banks and compare them to MAF g/s (or Hz) to see the fuelling changes due to changes in EOIT.

I'm also following the 2010 ECM with great interest as I may take that route, too.

[Michael_D]

The straightener made hz fluctuations less, so it may help. I just can't feel an improvement. I had to recalibrate because I went from the 102 to the 108.

Hopefully you can figure this out. I'm worn out. I'm also a lot fussier than others I guess. I drove a friend's GS with a roudy engine. He was gushing about how great it ran, "just like stock". I thought it ran like shit. Not nearly as good as mine.