Help cleaning up slight bucking @ 1600 rpms after cam

[turboffr]

Car runs great except for right at 1600 rpms. When I'm crusing I can feel a very slight, but noticeable bucking. Any suggestions on what to log to see what's going on? I did watch the timing and it's at 34 degrees where the bucking is happening. MAF curve is good and I'm running MAF only, no VE. Cam is a 228/232 in a C6 MN6 corvette. Idle is set to 850, start up airflow and base running aiflow tables have been adjusted. It starts up and idles fine. Tune is attached.

[turboffr]

ttt

[RWTD]

Try increasing/decreasing the spark. Make sure your idle airflow values are not too high, as well. You have raised them in that area, so that can definitely cause this.

Sometimes you can't eliminate it with aftermarket cams, as that can be the nature of the beast.

[Flash13Brandon]

Try increasing/decreasing the spark. Make sure your idle airflow values are not too high, as well. You have raised them in that area, so that can definitely cause this.

Sometimes you can't eliminate it with aftermarket cams, as that can be the nature of the beast.

So too much air in that RPM can cause bucking? For some reason, I was under the inclination that it was the opposite. Thanks for the info tho. Definitely helpful.

[Redline MS]

So too much air in that RPM can cause bucking? For some reason, I was under the inclination that it was the opposite. Thanks for the info tho. Definitely helpful.

Usually with a cam swap you increase the reversion of the engine through the intake. I would also look at the MAF hrtz and see how stable it looks at that MAF hrtz. Most likely you are in the 3000-3500 range and it might be moving quite a bit from what it was like when stock.

If you lambda is on I don't think its an air problem. Like James stated, timing "can" help this slightly. Timing makes torque and when the timing is too high you can amplify the surge even more. Knock 5-6 degrees and see what happens.

Howard

[E85 LSX]

I (and many others) have experienced the same problem after changing cams in an ls3. The bucking ended up being caused by lean misfires, apparently the ls3 is very sensitive to lean conditions, the closed loop switching is causeing the slight lean condition and results in misfire and the bucking you feel.

The solution is to add fuel in the area you have the bucking. Just run OL in that area and add fuel until the bucking stops. You should be able to eliminate 100% of the bucking.

[ayousef]

im trying to save changes to you're file with no luck, no idea why this is happening, however looking at you're file it gets quite obvious why its happening where its happening.

[hymey]

When the latest version is released I can start fiddling with the cracker tables but to do fix this you have to reduce airflow, ie because of reversion from the larger cam a 228 intake will get more reversion on a LS3 then a LS1.

Engine->Idle->Idle airflow-> Max Fail

It is 200, try reducing it. Maybe 10 at a time till you get effect I find some os hard limit is much lower then this for some reason gm sets it higher for no good reason. I have not seen an e38 with it set this high which signals it could be to much airflow, It has nothing to do with the base airflow tables so disregard that. Total throttle percentage is Max Fail plus pedal position percentage. So if you are cruising at 24.3% throttle you maybe applying 5.3% pedal position. What you need to do is keep reducing this until max fail drops so pedal position will build on a lower base tp%.

[Cruz-Lo]

When the latest version is released I can start fiddling with the cracker tables but to do fix this you have to reduce airflow, ie because of reversion from the larger cam a 228 intake will get more reversion on a LS3 then a LS1.

Engine->Idle->Idle airflow-> Max Fail

It is 200, try reducing it. Maybe 10 at a time till you get effect I find some os hard limit is much lower then this for some reason gm sets it higher for no good reason. I have not seen an e38 with it set this high which signals it could be to much airflow, It has nothing to do with the base airflow tables so disregard that. Total throttle percentage is Max Fail plus pedal position percentage. So if you are cruising at 24.3% throttle you maybe applying 5.3% pedal position. What you need to do is keep reducing this until max fail drops so pedal position will build on a lower base tp%.

Def going to give this a try!

[Mike@G-Force]

I (and many others) have experienced the same problem after changing cams in an ls3. The bucking ended up being caused by lean misfires, apparently the ls3 is very sensitive to lean conditions, the closed loop switching is causeing the slight lean condition and results in misfire and the bucking you feel.

The solution is to add fuel in the area you have the bucking. Just run OL in that area and add fuel until the bucking stops. You should be able to eliminate 100% of the bucking.

The mans speaks the truth. The OL method below 2000rpms will stop all surge.

[DSteck]

I pull timing out in the exact areas, and smooth the timing map... and can pretty much clean all of it out.

[Mike@G-Force]

I pull timing out in the exact areas, and smooth the timing map... and can pretty much clean all of it out.

Have you tried the open loop method. I command a 14.0-14.1 AFR at idle and light cruise. Runs like stock with little or no gas mileage loss.

[DSteck]

Have you tried the open loop method. I command a 14.0-14.1 AFR at idle and light cruise. Runs like stock with little or no gas mileage loss.

Haven't needed to. I'm not saying it doesn't work, because I did force my own car to open loop one time and ran it rich, and it drove great, but just never bothered to go with it.

[ScottyB]

I command a 14.0-14.1 AFR at idle and light cruise. Runs like stock with little or no gas mileage loss.

Newb here needing help with a 240+ cam @.050 in a 07 Z06. I would like to give what you are recommending a try. The guys that installed the cam took care of WOT tuning but at light load cruise I get this bucking/missing, even at 1800 RPMs. As soon as I just touch the throttle to put a little load on the engine all is smooth, even down at 1500. Just got HP Tuners a week ago and I have my tune downloaded to my laptop (saved a copy). Haven't flashed anything back to the car. Been reading books and the HP Tuners help but I cant find a place where OL is tied to RPMs. I am looking in Engine>Fuel Control>OL&CL. Am I in the right place? Close loop enable options all appear to be related to ECT or O2 readiness.

[E85 LSX]

Newb here needing help with a 240+ cam @.050 in a 07 Z06. I would like to give what you are recommending a try. The guys that installed the cam took care of WOT tuning but at light load cruise I get this bucking/missing, even at 1800 RPMs. As soon as I just touch the throttle to put a little load on the engine all is smooth, even down at 1500. Just got HP Tuners a week ago and I have my tune downloaded to my laptop (saved a copy). Haven't flashed anything back to the car. Been reading books and the HP Tuners help but I cant find a place where OL is tied to RPMs. I am looking in Engine>Fuel Control>OL&CL. Am I in the right place? Close loop enable options all appear to be related to ECT or O2 readiness.

One way to do is with PE. Set the PE enable TPS to O% from 1,000 to 2,000 rpm, then command a slightly richer mixure in this area to eliminate the lean misses. This will leave ur idle in closed loop which is how I left mine. You could also run OL in in idle as well though

[GregRexAdams]

Haven't needed to. I'm not saying it doesn't work, because I did force my own car to open loop one time and ran it rich, and it drove great, but just never bothered to go with it.

I agree with this, however I have only had success up to cams of around 7* overlap on a 346 and equivalent. I haven't tried the open loop method for larger cams, but around 16* I was unable to stop the bucking with just the timing.

For LS1 cars it seems to like a block of 27* timing in light cruise, LS2/7 cars seem to like 24*. I'm not sure on LS3 cars.