Well, let me start this off by saying that my cam surge has been very minimal since I finalized my tune, especially considering the size of my cam. It generally only happens if I let the revs drop to around 1000 RPM in 1st or 2nd gear, with a TPS in the 0-5% range. While still present at the same range in higher gears, it is much harder to notice because the lower torque multiplication of those gears does not allow the car to "surge". As such, I usually don't get any noticeable surge at all while driving, unless I purposefully drop the RPM's in a low gear in order to make the car start surging. Because of this I've been content to let sleeping dogs lie and haven't worried about cam surge at all, but lately I've been curious as to whether or not I could identify a parameter or group of parameters that I could change that would effect my surging in a positive or negative way. Tonight after work I spent a bit of time experimenting, and I thought I'd share my findings.

What I've noticed in previous logs of surging is that the IAC position, spark advance, and MAP all oscillate in time with the surge. What was not readily apparent was whether or not these were all just symptoms of cam surge, or if possible one was a contributing factor. My first thought was that perhaps spark advance was oscillating between the High Octane spark table and the Idle spark tables when the TPS dropped to around the 1.5% TPS threshold for spark. To eliminate this, I correlated the tables and modified them to match. This produced no noticeable effect.

Next I tried modifying the Overspeed and Underspeed spark tables, thinking perhaps that they were overcompensating causing the surging. First I lowered the values, and then increased them, again with no noticeable effect. I even tried zeroing these two table out, but of course I couldn't even achieve a stable idle after that.

The final step I took to eliminate spark advance as the cause of the surging was to use the real time controls in HPTuner to command a steady advance. I commanded 35* of absolute spark, and surging was still unaffected. I also verified in the scanner that the spark advance was indeed locked at 35*. It would appear that the spark advance oscillations are nothing more than the PCM reacting to the surging, and not actually a cause of the surging.

My next step was to eliminate the IAC motor from the equation. I unplugged the IAC motor at hot idle, and with it unplugged I found that my surging was completely unaffected. It would seem that the IAC position oscillations, like the spark advance oscillations, are only the PCM reacting to the surging.

It would appear from this experiment that the PCM's two main ways of regulating engine RPM (spark advance and the IAC motor) are not responsible for causing surging.

There was one last thing I wanted to try before calling it a night, and that was seeing how running in SD would effect the surging. I ran in SD prior to correcting my MAF table for quite some time, and have a dead on SD tune, so it was simply a matter of unplugging the MAF and driving. It seemed that at last I was on to something. I could still make the car surge in SD, but the 0-5% TPS "dead zone" where the surging would occur in MAF operation was much smaller. At about 1000 RPM and under, I could only get the car to surge in SD when the TPS was between 1-2%. Anything more or less and the car would not surge. In fact, in SD I was able to idle down the road in 1st gear, foot off the gas, with absolutely no surging. This was impossible to replicate in MAF operation. This of course shows that whatever the state or condition that causes surging, MAF operation is much more sensitive to it than the SD calc.

All in all, this seems to affirm my belief that the number one cause of surging is simply low RPM intake port reversion, although I'm sure other conclusions could be drawn. Anybody have any other ideas?

 

The MAP and fueling I think is another element of it, that
should be predominant at lower RPM. The VE table gets
atention w/ RPM but I haven't heard of anyone playing
in the MAP dimension. If you traverse a steep VE face
following MAP deflection, that can be enough of a kicker
to make things unstable (high MAP -> more fuel -> less
efficient -> RPM drop -> higher MAP...).

In the low RPM regions you might want to try flattening
the VE values along the MAP columns and see. I can't
see why (other than static flow / runner drag) why low
RPM VE would follow MAP much at all, but the table is
profiled that way.

 

can you sum that up and tell us what cam you have?

i was just curious of the problem and didnt have time to read through that. to fix my bucking first thing was to get a WB and tune idle fuel correctly, then tune idle airflow and it fixed it with a 230/232 cam

 

Closed loop SD tuning and running with L-Trims turned off has made my car a joy to drive. My S-Trims pretty much stay between 0 and -3 in all the major cells. Having L-Trims zeroed keeps a lot of funky fueling from happening between cells. Keeps it all smooth.

 

I am not a tuning genius but I have this same problem and have thought about it for quite some time now and come to the conclusion that the O2's are to blame. I think that this is a lack of calibration of the O2's. After installing a comp cam 236/236 602 602 114+2 and longtubes with the o2's in the collector I eneded up with the same problem. I too have tuned in sd until I don't think that I can get any closer. So here is my take on it. If you have a large cam with any overlap more than the stock one you have a unmeasured amount of raw(unburned) gas that is forced out of your exhaust port and into the header. This in turn makes the sensor read rich due to its cooling affect, so the computer tries to lean the mixture and correct it. Now you have a lean mixture that needs to be corrected but there is still raw gas in your exhaust system due to your cam's lope. This is a basic example but should work for theory. So if you can figure out some way to make the measurement of the rich mixture with raw gas at idle corrected and do the same for the lean mixture plus raw fuel then you the ecm should be able to correct the rich or lean condition. Next problem. Now your O2 is in a longtubes collector that is 18" to 20" past the initial position that gm tuned it for not to mention if it is like mine it is in a 3" collector and the same amount of the sensor is inside the tube only now the tube is almost twice the diameter and one primary is running the whole show. So a rich or lean condition with that much distance seems like it would be less due to the lack of pressure(droping the temp) and the distance allowing the exhaust to cool also dropping the temp. I am unsure how to do any testing to prove my theroy but it makes since to me. If you recalibrate your injector, your VEtable, your maf, why not recalibrate your 02's for their new environment also? Also something else that has made me notice this is my oscillation at idle and low rpm's is considerably slower than at mid to high rpm. Hope this isn't all B.S.and can help someone make progress with this issue or someone can help me and put me in the correct direction.

..RJ..

 

This is an excellent point IMHO. I'm working on a 239/242 110lsa cam in a stock head stock shortblock z06 at the moment and i'm starting to think a big cam is going to be impossible to get all of these anomolies out of. For instance, I had to watch my idle cells very closely cause my sensor sais it's idleing to lean but i know it wasn't idleing too lean cause it smelled like the exon valdeez crashed into the back of this car. So I simply just leaned these areas (75-85 kPa and 800 1200 rpm) out and added lots of timing and it fixed the problem there. I think I still have some other issues to address with different idle tables but I don't think you can make something this big drive like stock, epecially with the stock gears that this z06 has (it does have a more agressive 1st, 2nd, 3rd gear).

 

o2 oscillation can cause major problems if they dont oscillate well.

 

Don't blame the O2s before you try running in Open Loop. To isolate my surging, I would eliminate certain variables from the equation. Like doing away with the MAF (helped), unplugging the IAC motor (didn't help), holding timing fixed at the point the motor surged the least (28-30 degrees at low TPS worked best for me). I even went pure Open Loop to eliminate the O2 sensors from the equation. Guess what? It didn't make any difference in my car. But turning off the L-trims did help so that's why I run Closed Loop speed density. BTW, I run the Bosch 13111 O2 sensors.

 

I've ruled out cam surge being an O2 issue, at least in my case. I get just as much surge in open loop as I do in closed loop, and that rules out any monkey business from the O2's. And they do oscillate quite nicely when I run in closed loop. Doing some WB logging in open loop my fueling is spot on, so I don't see that as a factor either.

Like I mentioned before, I have almost no cam surge at all, and have to purposefully make it happen to get the car to surge. I'm happy with where my tune is at as far as surge, I'm just trying to dig a little deeper to uncover the root cause/causes. In my case, I've ruled out fueling/O2's, spark advance, and IAC operations. At this point the only thing that makes sense to me is reversion. Now, I don't dispute the fact that other issues can exacerbate the problem; i.e.- incorrect RAF, timing, fueling, etc. I have simply eliminated those in my particular case, and I feel that I'm down to the actual physical characteristics of engine operation, and not a parameter that can be adjusted via tuning.

My current view is more reversion = more surge. This would also seem to explain why the MAF is more sensitive to this than SD, since the MAF does not handle rapid changes in airflow very well. I think that surge can be minimized through proper tuning, but that a large cam with intake port reversion will always surge to some extent.

 

As I said before I am not sure of the 02's being to blame just a thought. I have read that others are having problems with surging after replacing manifolds w/ longtubes only. Could this be due to 02's not being calibrated correctly? Either way how would you recalibrate them? There has to be some change in a rich and lean condition due to less pressure and sensor location. Does anyone have a log showing all of the things 02's are doing on a stock car? on a cam only no header car and one of the same car with cam and headers? If so I would love to do a comparison of the three or even just one stock and then the same car with a big cam

 

You can change the O2 switchpoint by the airflow mode
table and you can change what "mode" you are in, at
what airflow. But I think the problem is more one of
sensor response time and that the PCM tries too hard
when the sensor just doesn't switch worth ****. The
proportional fuel stuff affects the swing over-center and
I think this itself may be your surge, the fuel dithering
that gets awful slow and heavy when the sensors don't
turn it back smartly. You might want to turn that off as
another dissection line.

 

Definitely. Temperature has a big effect on the operation of O2 sensors, and temperature change will change the voltage output of your O2's for a given AFR. The system was designed for the O2's to be accurate in the stock locations on the manifolds, near the exhaust ports where they get nice and hot. They do not reach the same operating temp at the end of LT's because they're so far away from the heat of the exhaust ports. Hence, what they read as 14.7:1 in the manifolds is different from what they now read as 14.7:1 at the LT collectors. What my O2's read as 14.7:1 is actually about 15.4:1 according to the WB. The cooler operating temp can also cause them to not oscillate properly, but mine do okay in that respect. I've done a few LT installs on otherwise stock LS1's, but I've never seen it cause surging. Not that it doesn't happen; that's just my experience.

I'm not 100% sure how (or even if) you could accurately correct for this. I suppose you could experiment with changing the O2 rich/lean switch point. Or perhaps the voltage going to the O2 heater could be increased in an effort to keep them hotter? Sounds like a good electronics project to me.

 

i can make any manual car surge, just dont try to do it

 

I think you're missing my point. This isn't a "help me fix my surge" thread. I've tuned out 99% of the surge I initially experienced after installing my cam, and it's as good as it's going to get. This was instead an informative thread outlining some of the methods I used to try to determine what factor or factors are the root cause of cam surge, and to get some other peoples ideas.

 

ok got ya, i was thinking you were trying to get rid of it all

 

I didn't mean to hord your thread either I was just hopeing to possibly add some light. I'll try to change some of those things this weekend if my 10-bolt decides to let me limp around a few more hours. I found your experiments helpful but stil have ?'s. I have noticed that if I cut my truck off then start it right back up, my surge is much worse than before. ok now let say I drive 25 miles now its back to the way it was before where it isn't as bad. What do you think that may be? Oh yeh and when I first started tuning my ve, if I cut the truck off then started it again my lt-trims where always way off then after driving would return back to near 0. I don't know if this info could help with the surging problem or if it was just a freak incident but either way the ve doesn't do it now but the surging still remains.

 

As far as it being worse immediatley after starting, I'd guess that it might be an issue with open loop fueling, since it won't go into closed loop for a little bit after starting, even when warmed up. I would try leaning out the open loop table and seeing how that goes.

As for the trims, I've seen mine do that when they're not fully learned. Even when they are learned, they can vary quite a bit. Also, your trims when the car isn't fully warmed up will be different than your trims are when it is warmed up.

 

If search was working, you'd be able to find more information to back your theory.


On the same topic, I fattened up my surge/bucking areas and it helped quite a bit. Wasn't worth the increased cost in fuel, but it helped.