Has anyone figured out why cams with alot of overlap(10 degrees +) tend to surge @ low RPM and low throttle position? I'd love to find a solution.
Phil

 

Mine only surges for a couple of seconds on initial cold start (40 degrees or less). Otherwise it's good. I have no problems in gear while driving. I assume you've tried all of the usual adjustments?

 

That is usually corrected with a little more (steady) timing than stock, the right fueling, and some tweaking to the cracker/follower tables.

 

Are you running closed loop ???? Usually its a mix of things. some cars you can make better and some cars you can totally fix. Really depends on a ton of factors.

 

Exactly.

Is this car running in open loop...I assume so....

 

If you tuned the VE table, added more timing in the idle regions(over stock), raised the Idle rpm and tuned the base idle airflow, it really shouldn't do it at all.

 

Open loop speed density
Also take a look at something like efilive os5 with alpha-n fueling. So MAP and MAF dont mess you around.
Loads of guys have had excellent results with that. You can use it say under 1200 RPM and return to MAP SD mode over 1200rpm etc.

 

Its running closed loop, I wonder if the O2s are causing it to surge.

When I say surge....
Drive along in 4th gear @ 1200-1600 Rpm with little or no gas the car will buck or pulse. Every car does it, big overlap seems to do it more.
Phil

 

Throttle by wire car.

 

you are flooding the motor with fuel running in closed loop. All that overlap tricks the 02 signal into looking lean. In fact Widebands will often show lean very lean 17.0:1 at low rpm 1000-2800 rpm range. To fix this is often have to lean the engine up alot at low rpm add more throttle follower and rpm follwer airflow and pull a bit of timming which will make the engine look even leaner. Most of the time this will help if not correct the issue but if you camhsaft is really really large then you might just be able to improve it.

 

Very interesting...Thanks.

 

The problem is not the MAf. The problem is that most tunners have zero clue as to what they are actually doing. You must remeber that 02 sensors only measure oxygen content. to really figure out the Af ratoi you must figure fuel flow and have an actual measure of airflow. SD fixs nothing.

 

346, open loop, SD. DFCO is inactive.
Fly by Wire.
239/251, 106 lsa

1600 - 2000 rpm will surge, at very light or zero throttle if my throttle cracker g/sec is too little. Otherwise it doesn't surge. FWIW.

 

So you are saying that your cracker being too low causes you to have this problem? Could you post the values that you are running in the cracker. I have my cracker completely zeroed out. I have the problem before I zeroed the cracker but I never really played with the values. I am most interested in this. I wouldn't mind looking at your folower table also if possible. I have HPTUNERS but if youare using something else, just e-mail me an excel or word doc or post the raw data here. Thanks in advance. bellos98@yahoo.com

 

i had issues with surge and zeroing out my throttle cracker did nothing to that, air flow/timing was the key

 

AMEN!
well...almost nothing. i did have one car that would not idle or run partial throttle in maf, no matter how many MAF retunes i did. in SD it ran very smooth (at least relatively speaking for a huge cam/heads/intake/stall).
by now i should be able to map airflow calculated from SD mode onto the MAF table, but back that i didn't know how to do such tricks. more traditional MAF tuning tricks just wouldn't get it even just in the ballpark. i'm guessing that was reversion saying hello--rare but it does happen

 

Too much Throttle cracker can cause the surging effect too.

 

If any of you guys are interested, please check out this thread with the problem that I am having pertaining to this subject. What really kills me is that the cam that I am running is not that big (for a 402) compared to some others that I have seen that claim to have no issues with surging. Any input would be greatly appreciated. This vehicle needs to become my daily driver sooner than later as I am turning in a lease. It is very painful to try and slip a race clutch (Spec 5) in order to smooth the bucking in the problem areas. Thanks in advance.

http://www.hptuners.com/forum/showth...6386#post66386

 

Curious find by Jimmyblue who noticed the spikes and lows in stock cracker table.
Left is stock and right is smoothed out.
It helped me tremendeously.
https://ls1tech.com/forums/pcm-diagnostics-tuning/456413-weirdness-throttle-cracker-stalling-fix.html

 

Added 5* in the 400 to 1600 .08 to .16 range and it made a big difference for me.