'08 Black Z06
PCM Tuned, LG super RAM, AR Headers, Hoosier DR2 295-55-15, MSD Atomic air force intake, Iceman 7.0 cam
Best N/A E.T. : 8.836
Best N/A Mp/h : 159.75
DA for this pass: 0'
There are 2 potential sources to this problem and I think some of the people here are talking about one and not the other.
The problem I believe the OP and myself are trying to solve is an extreme oscillation in spark. As I noted a couple posts ago, I was going to try getting rid of the AC torque reduction. This was not the source of the problem on my car. What ended up eliminating the oscillating spark (and therefore, the harsh bucking at low charge) was the spark airmass blend feature. Typically a spark blend is blending between 2 different spark surfaces, such as Part Throttle and Idle. On the contrary, the HP tuners description indicates that this is actually a predictive spark feature, but it does not give any detail of how this feature works. Lowering the Spark Airmass Blend to 0.5 from 1.0 did the trick for me. My guess is that the ECU processes MAF signal and MAP signals at 10 or 20ms and we're not datalogging it that quickly so we do not see the true magnitude of the fluctuations in airflow or pressure which occurs with the high overlap cam profiles. My speculation is that the spark airmass blend is calculated based on a rate of change in the MAP signal in an effort to help transient ignition timing. Our erratic idle is too much for it.
Try lowering your spark airmass blend and see if that helps.
Now, I still have the normal surge that comes from high overlap, high lift cam profiles, but my spark stays very constant. The surge again is just the nature of the beast. The cylinder pressures become very erratic. You do not see the same pressure from firing event to firing event and thus each combustion event generates a different torque. The VE is very low because the cylinders are not filling properly and with high overlap you also get reversion and charge dilution from EGR. This all leads to less dense air and a very very slow burn rate. Slow burn rate means you need a great deal of spark advance to maximize combustion efficiency. This is probably why Greg Banish said to increase spark advance. Thats fine as long as your combustion events are stable from cycle to cycle. However, in an unstable condition you can decrease the magnitude of the cylinder pressure peaks (and thus erratic torque) by retarding the timing. You're burning more fuel, but making your engine run smoother. This is why HoP's 36-38deg helped eliminate his surge. You only want to pull enough to make you happy with driveability, otherwise you're just wasting fuel.
Last edited by Sébast19X; 10-05-2012 at 10:08 AM.
'08 Black Z06
PCM Tuned, LG super RAM, AR Headers, Hoosier DR2 295-55-15, MSD Atomic air force intake, Iceman 7.0 cam
Best N/A E.T. : 8.836
Best N/A Mp/h : 159.75
DA for this pass: 0'
pics added above
'08 Black Z06
PCM Tuned, LG super RAM, AR Headers, Hoosier DR2 295-55-15, MSD Atomic air force intake, Iceman 7.0 cam
Best N/A E.T. : 8.836
Best N/A Mp/h : 159.75
DA for this pass: 0'
go to engine then idle then then air flow then Base runnin min open then scrol over to 8000 put 34 all the way down then use interpot between bound save file, load you surg will be gone
Unless your menu/table titles are slightly different than mine, I'm not sure I follow your logic. Engine>Idle>Airflow>Base Running Airflow>Airflow Final Minimum is that only thing that comes close to this description. That table is an airflow table...34 lb/min at 8000RPM wouldn't make sense and the ECU won't allow that high of a number anyways. This leads me to believe I'm not following your instructions correctly. Can you tell me the exact name of the table to which you are referring please?
Can I make a suggestion to maybe fix the surging as per frames 6500-6900, in the DFCO paramteters go into the Enable CylAir and Disable CylAir and set all values to 8.19, see if that helps. It looks like it should be going into DFCO but it wont because the dynamic cylinder air is higher due to the engine mods.
2010 GXP Maloo ute, LS3, 6L80E.
MM heads, 240/252@50 solid cam, 12.75:1 compression, 4500 Dominator converter, 3.46 rears.
Shooting for 10s eventually.
i agree dfco is engaging and it just does not only pull fuel it pulls timing as well disable it temp wise ie 258 problem should be gone hth
Gray Ghost- The abomination. 2007 Chevrolet Silverado CCSB. 98mm turbo, nitrous, 428LSX, Rossler 80E with a brake. Finally finished. 23 psi, no numbers, Slow as hell.
PBM G8- Aluminum 364, twin Precision 67/66 turbos, 6L90 trans swap, CTS-V/Vaporworx fuel system, slowly making progress.
Dads 2011 CTS-V- Stock bottom end, stock heads, LS9 cam, pullies, ported blower, ported TB, D3 goodies, and lots of nitrous.
618/618 motor
906/862 spray
Caterpillar 50 Forklift- Duramax swap