Cammed LS3 Surging

[andrewzpsu]

Well I finally cammed my LS3, it isn't too big of a cam either, 230/234 114. When I first took it out after putting in the cam, on the bolt on tune none the less, it drove almost perfect. At light throttle right before no throttle there was some surgining/bucking.

After driving it a bit more the surging/bucking has become increasingly evident and I began to try to tune it out.

Refining the spark tables, coast down etc, do not seem to help much (they help, just not enough). Fueling seemed to be the thing that really and truly helped it. I programmed the 02 sensors to change the switch point to like 800mv at idle and low throttle instead of the 400. That seemed to help a bit, but I think I'm still getting some surging.

When rich, the car idles like it is stock. You would not be able to tell its cammed. However the surging is really starting to piss me off.

Is there anything I should look for in the tune? Or anything I should check at the car that would explain the surging?

Thanks

[DSteck]

Pull timing out of the main spark table. Sometimes up to 10 or 15 degrees. I don't know exactly what is happening, but for some reason, timing gets sporadically yanked when you're at low load, low throttle conditions. I haven't been able to figure out if it's just swapping back and forth between main spark and idle/coastdown tables, or if for some reason the adaptive spark tables are kicking in.

Since you do some have overlap, it will have a little instability that you can't do anything about. There's no reason it should be uncomfortable, though. My cam has 23º of overlap, but the car still drives acceptable.

Richening up a big cam is one of the ways to help, which is what you did with the switch points.

[andrewzpsu]

I believe it had a lot to do with adaptive spark tables, but then when I set the spark the same on all accounts I still got some bucking even though the spark table line was straight. In addition I then put it in open loop and still got it. I wish we had the same accessibility that we had with the LS1s when we could command AFR and Spark...

[wstaab]

MAF tables need to have accurate airflow at low throttle/low rpm or surging will be there. Have you tuned your MAF tables by logging your LTFT error?

[andrewzpsu]

MAF tables need to have accurate airflow at low throttle/low rpm or surging will be there. Have you tuned your MAF tables by logging your LTFT error?

Yes. I disable LTFT actually and use STFTs so its faster logging and doesn't mess up my WOT.

I'm going to give that a quick second look though over my lunch break.

Guess I should set my O2 sensors back to normal for the time being then.

[5_Liter_Eater]

FYI: Adaptive spark is only present when speed = 0.

[andrewzpsu]

FYI: Adaptive spark is only present when speed = 0.

Thats what I thought. It seems to be switching between some tables then like the costdown table and then going immediately back to the regular table.

[Ben Diss]

FYI: Adaptive spark is only present when speed = 0.

True for Idle Adaptive Spark, but there's also Coastdown Adaptive Spark.

[DSteck]

FYI: Adaptive spark is only present when speed = 0.

Half-truth. There are multiple adaptive spark tables.

[wstaab]

Guess I should set my O2 sensors back to normal for the time being then.

500mV is a good value for the O2 rich/lean switch over voltage table across all cells for a cammed motor. Does not allow the A/F ratio to go quite as lean which helps the idle and surging problem. Try more timing in your base idle tables (22 to 24 degrees) from 600 to 1200 rpm up to .48 g/cyl. Take some timing out of your over and under adaptive idle spark control tables. Start with + or - 6 degrees and work up until the results improve.

[5_Liter_Eater]

Didn't know that there was coastdown adaptive spark. Thanks.

[DSteck]

What idle speed are you trying to use right now, btw?

[andrewzpsu]

Idle is at 800 rpms. But my surge is just about everywhere at light throttle. Which leads me to believe it is a fueling and spark issue.

Timing is real low at the moment, although I've had it real high too with no difference.

I'll double check the coast stuff again, as that would make sense... but I'm pretty sure I already limited the amount it can take out there.

[Ben Diss]

Idle is at 800 rpms. But my surge is just about everywhere at light throttle. Which leads me to believe it is a fueling and spark issue.

Timing is real low at the moment, although I've had it real high too with no difference.

I'll double check the coast stuff again, as that would make sense... but I'm pretty sure I already limited the amount it can take out there.

Put the car into Competive Mode and see if it's any better.

I've been chasing an issue with my '07 LS2 that I can't seem to nail down. Under very, very light throttle in 2nd or 3rd gear I get some bucking between 1200-1800 RPM. I think what's happening is the throttle is so light that it's switching between coastdown and drive. In higher gears, the load is a little higher and I don't get any bucking.

Comp mode changes the throttle curve making the throttle less sensitive near idle. This seems to help some.

[andrewzpsu]

Put the car into Competive Mode and see if it's any better.

I've been chasing an issue with my '07 LS2 that I can't seem to nail down. Under very, very light throttle in 2nd or 3rd gear I get some bucking between 1200-1800 RPM. I think what's happening is the throttle is so light that it's switching between coastdown and drive. In higher gears, the load is a little higher and I don't get any bucking.

Comp mode changes the throttle curve making the throttle less sensitive near idle. This seems to help some.

I'll give that a shot. I seem to get it more in the higher gears than the lower gears though. My goal is of course to have it no where and with it in normal traction mode lol.

[DSteck]

Drop main spark to about 25º in the problem areas. See if it does anything. Set your adaptive controls to stock.

[andrewzpsu]

Drop main spark to about 25º in the problem areas. See if it does anything. Set your adaptive controls to stock.

I'll give it a shot.

So far nothing is working.

I've had the problem areas from 0* to 30*. Right now its at 27*...

It isn't showing any knock retard... but who knows.

Its surging like anywhere it can. Which is like anywhere under 2000 rpms.

[ktoonsez]

Show me your "Airflow Final Minimum", this is what I adjusted to get rid of my surging. It ended up being that the values were too high.

[andrewzpsu]

Show me your "Airflow Final Minimum", this is what I adjusted to get rid of my surging. It ended up being that the values were too high.

I'll post the tune later after I give some of these suggestions a shot.

I'm going to start a new tune after work from the stock tune and see what I can do with that.

From the stock table I imagine you have added fuel, correct?

Also, for a manual, do the gear airflow minimums actually do anything... it doesn't really feel like they do.

[ktoonsez]

I did not add fuel using any fueling tables. I simply set my AFR to where I liked the way the car idled and cruised using the VE and MAF tables (after setting the minimum airflow table). The minimum airflow tables work the same way on auto and manual, it simply represents the minimum amount of air to let in (basically throttle body opening %). In my case I was letting in too much air causing a surge condition by trying to cram too much air down its throat, so to speak.