Cammed LS3 Surging

[Ben Diss]

This might help.

There are several modes that tables refer to. On my manual '07 with a E38 PCM, I've figured out the following:

InGear: gear selected, clutch out.
Park/Neutral: shift lever in neutral or clutch in.
Coastdown: gear selected, clutch out, foot off pedal

The min airflow table does effect each gear differently. It is the min air fed to the engine during coastdown. On launch, it is also the min air. On a soft launch, this prevents a stall if you're less than perfect with your feet.

[RWTD]

Andrew, my guess is that you're running the stock VE tables, right? Since most likely that is the case, just eliminate the VE algorithms altogether right now and run direct MAF mode, and then properly calibrate the MAF transfer in, as needed. If you do NOT do this, and instead still try to run off the factory VE, I can assure you that the vehicle will NEVER have perfect drivability. I seriously doubt you will desire learning how to dial in the VE on your E38, especially considering it'll take you weeks upon weeks, maybe even months, to learn it and actually tune it this way.

To disable VE (yes, the vehicle will still run 100% normal in pure MAF mode), do this:

Go to Engine, General, Airflow, Dynamic Airflow, and set "High RPM Disable" to 100 and "High RPM Re-enable" to 0.

Trust me, try this, and you'll see that is corrects a LOT of your issues right off the bat. The rest will be dialing in the spark tables, and also the airflow values.

Now, when and if you wanna try to learn the VE, see here:

http://www.hptuners.com/forum/showthread.php?t=20539

[DSteck]

I've been running pure MAF for the last year, and it's been working great.

[andrewzpsu]

I've been running MAF only since I put headers on the car. And yes, I have tuned the car using the VE table as well.

I'm really starting to think my issue is mechanical. as my MAF table is spot on.

[Chris442]

I've had a similar issue on both an LS7 car and my LS2 GTO, both with relatively mild cams. After I put the cam in my LS2 about 2 years ago, I fought this same problem using many of the same techniques that people have described here. Smoothing the timing between all the different tables helped some, but didn't cure it. Here's a post I made about it back in 07. Although I state then that it was only a few hundred revs above idle, I've seen surging like that as high as 1600-1700. That is just not right for a 224/226 111 LSA cam in an LS2. Eventually I decided I'd just have to drive around it, as it was just a side effect of having a cam in the car.

Fast forward to now, and I'm dialing my Dad's cammed LS7 '68 Camaro. I has working on the VE with trims, when I notice a similar surging to my GTO. Looking at the logs I notice that the timing spikes correlate with Torque Management Advance on the scanner--interesting. You cans see more here. Today I find out that these timing dips are caused by M6 Spark Smoothing. This smoothed out the LS7 this morning, so I tried it on the LS2 tonight with the same results. I was running the LS2 in 6th at 1000 rpm with no surging or bucking, almost like stock.

One more thing that causes surging/bucking on the LS7 tune is DFCO. On the LS7 it was setup to turn on basically by airflow in g/cyl, whereas in the GTO it was based on closed throttle and rpm. The LS7 would allow DFCO to start with 3-4% pedal position, so it was going on/off at those ETC pedal positions making the car surge a bit from the extreme timing/fueling changes. Changing the setup to be more like my LS2 should straighten that right out.

Try disabling the M6 Spark Smoothing.

[andrewzpsu]

I've had a similar issue on both an LS7 car and my LS2 GTO, both with relatively mild cams. After I put the cam in my LS2 about 2 years ago, I fought this same problem using many of the same techniques that people have described here. Smoothing the timing between all the different tables helped some, but didn't cure it. Here's a post I made about it back in 07. Although I state then that it was only a few hundred revs above idle, I've seen surging like that as high as 1600-1700. That is just not right for a 224/226 111 LSA cam in an LS2. Eventually I decided I'd just have to drive around it, as it was just a side effect of having a cam in the car.

Fast forward to now, and I'm dialing my Dad's cammed LS7 '68 Camaro. I has working on the VE with trims, when I notice a similar surging to my GTO. Looking at the logs I notice that the timing spikes correlate with Torque Management Advance on the scanner--interesting. You cans see more here. Today I find out that these timing dips are caused by M6 Spark Smoothing. This smoothed out the LS7 this morning, so I tried it on the LS2 tonight with the same results. I was running the LS2 in 6th at 1000 rpm with no surging or bucking, almost like stock.

One more thing that causes surging/bucking on the LS7 tune is DFCO. On the LS7 it was setup to turn on basically by airflow in g/cyl, whereas in the GTO it was based on closed throttle and rpm. The LS7 would allow DFCO to start with 3-4% pedal position, so it was going on/off at those ETC pedal positions making the car surge a bit from the extreme timing/fueling changes. Changing the setup to be more like my LS2 should straighten that right out.

Try disabling the M6 Spark Smoothing.

I'll check out DFCO. That sounds very interesting, especially if the entry spark and exit spark are waaay off (not infront of hp tuners at the moment).

I disabled the spark smoothing a while ago and it helped, but then it seemed to have come back a little after that. But I started from scratch not too long ago and go it pretty smooth, however I did not disable the spark smoothing yet. I'll give it a shot now and see if it helps.

[andrewzpsu]

Its much smoother without the M6 spark smoothing. However I still think the blade shuts too far so I gotta play with the minimum airflow tables again.

In all honesty I think what needs to be done to get it right is more airflow and less timing. As more airflow with that timing seems to make it "coast" or have a phantom cruise control.

I'll be giving that a shot soon.

[yellz06]

I still think the car will buck and surge less with the VE Enabled.. the maf cannot actually compensate for every situation where turbulence exists like the instability in the cam at low speeds.

That means that a good ve tune will actually solve most of the bucking issues. O2 sensors take a split sec to adjust in fueling and that "perpetuates" the surging. It does solve a lot of things running in pure maf mode, but honestly... VE/MAF is the way to go.