Horrible bucking, I can't make it stop, need help

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10-23-2009
jimmypop13

Horrible bucking, I can't make it stop, need help

I don't know what to do to fix the bucking on my car. It's really bad between 1200-2000rpm and probably the worst right in the middle of that range. I tried raising the timing in that area way up because I read that can help but it's not working. My whole drivetrain just bangs back in forth when it does it and it sounds horrible. I know I'm wearing out all sorts of parts. In fact, I just had new gears installed and LMR had to replace the axles too because they said they were so worn down. I'm sure this bucking for 2 years probably caused a lot of it.
The only ideas I have left are more fuel, which would probably just be canceled out by my STFT's, or super low timing like 22-24*, because I tried low 30s and it didn't help at all.
I put brand new bosch o2 sensors in. Didn't do anything. But I noticed in the scan, the mV values for them shoot way up and down really fast in the bad spots. Maybe there's something to that?
Please check out my tune and log to see if you can help me out.
Thanks

-Chris
10-23-2009
jimmypop13

I'm not sure if my wideband was set up right in that log but it's working now and on my latest run, my brand new bosch o2's said to pull 10% fuel in that area while my PLX wideband said to add almost that much fuel. This is nutty!
10-23-2009
jimmypop13

How do I disable closed loop without unplugging the o2 sensors? just max CL enable temp?
10-23-2009
KLUG'S SS

Quote:

Originally Posted by jimmypop13

How do I disable closed loop without unplugging the o2 sensors? just max CL enable temp?

Yes that should do it since you have a GenIII, the fourth Gen's have a couple more tables to address but you've got an 02 so you should be good to go with that. Also make sure to reset fuel trims before you start logging in OL.
10-23-2009
Frost

Why beta???
10-23-2009
jimmypop13

Quote:

Originally Posted by Frost

Why beta???

Because I also have a 2009 HHR SS which isn't supported otherwise

I went OLSD and using the wideband, the bucking got better but it's still there. I messed with the timing changing it to 24, 30 and then to 40. It was definitely better around 30.
10-23-2009
DSteck

A lot of people bitch about running very low timing and claim it takes away torque... but they've probably never personally tried it. That's how I cleaned mine up (higher cylinder loads in sub 2000rpm areas have more timing), and I have no problems passing people in 6th gear. You just really have to finesse the table.
10-24-2009
Frost

What is your idle airflow value at full operating temp? (I can't see it)

Goto your throttle cracker table. From about 40 MPH and UP, ZERO out the 1K column and the rest of them up to 2200RPMs. In the 400 RPM column, put in a number around 1.6. This is a 'catch' in case you get a big sag.

Bucking is usually more airflow than timing. 30 degrees is very high though. Lowering timing is where I go when airflow is correct and I still get buck. 18deg would not be out of question if the buck is severe.
10-24-2009
jimmypop13

Quote:

Originally Posted by Frost

What is your idle airflow value at full operating temp? (I can't see it)

Goto your throttle cracker table. From about 40 MPH and UP, ZERO out the 1K column and the rest of them up to 2200RPMs. In the 400 RPM column, put in a number around 1.6. This is a 'catch' in case you get a big sag.

Bucking is usually more airflow than timing. 30 degrees is very high though. Lowering timing is where I go when airflow is correct and I still get buck. 18deg would not be out of question if the buck is severe.

I'm gonna try lowering the timing again. When I tried before with the 24*, I wasn't as good at getting the ve correct like afterwards when I tried 30* since I had more practice at it. My idle is at 22* so would it be bad to go lower than that when driving in that 1000-2000rpm range?

With throttle cracker I'll give it a try but right now my whole table is zero'd out and disabled. I've been trying to get the car to run good and not die with just throttle follower.

I'll try to get up a better log soon bc there were some problems in my cfg file.
Thanks for the help
10-24-2009
Frost

Quote:

Originally Posted by Frost

What is your idle airflow value at full operating temp? (I can't see it)....

Answer this. ^

If your TC table is zero'd out, there are still airflow adders like throttle-follower but most likely your idle airflow is too high. If you don't have a DBW TB, I would still use the TC in at least the 400 and 1000 RPM columns.
10-24-2009
99LS1SS

Quote:

Originally Posted by Frost

Answer this. ^

If your TC table is zero'd out, there are still airflow adders like throttle-follower but most likely your idle airflow is too high. If you don't have a DBW TB, I would still use the TC in at least the 400 and 1000 RPM columns.

Here is his Idle Airflow vs. Coolant Temp

Code:

Labels -40 -18 3 25 46 68 90 111 133 154 176 198 219 241 262 284 Gear 4.1006 3.7713 3.7368 3.7038 3.6804 2.4704 1.6759 1.4323 1.2362 1.1631 1.0915 1.0913 1.0913 1.0913 1.0913 1.0913 P/N 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
10-24-2009
Frost

That seems reasonable... Does desired airflow = what you are set for there? (STITs and LTITs?)
10-25-2009
jimmypop13

Quote:

Originally Posted by Frost

That seems reasonable... Does desired airflow = what you are set for there? (STITs and LTITs?)

It did but then I went open loop yesterday and added some fuel because my wideband said I was lean while my NB's were saying I was rich. I guess I'll run Russ K's idle config again in the morning to make sure I STIT's are at 0.

I did some testing today and found my car seemed to like 22-24* timing the best in the bad areas. Going down to 18-20* seemed like it was either the same or slightly worse. I messed with fuel and used the VE multiplier table to go as low as 13.5/1 but it didn't clean it up. I'm gonna try messing with the throttle cracker table tomorrow like Frost was mentioning. If I can't figure this out soon, I think I'm gonna look at getting Patrick to spec me another cam that won't have bucking with my setup. He tuned it himself probably a year and a half to two years ago and didn't get rid of the bucking either. I was just hoping a lot of time would help but maybe that's just part of having 16* overlap

-Chris
10-25-2009
Frost

I had a fit a few weeks back with a smaller 228 233 on a 111LSA. It's crazy. The same week I had an MS4 car (high 230s intake 240s ex on a 111) and as they always are, it was a breeze and has no buck. That smaller cam though that I first describe has been harder to get the buck out than anything I have messed with... and it's SMALL! Pat G specs cams that make power and he loves those tighter LSAs, but having to tune out buck is something that comes with the territory.
10-25-2009
jimmypop13

Quote:

Originally Posted by Frost

I had a fit a few weeks back with a smaller 228 233 on a 111LSA. It's crazy. The same week I had an MS4 car (high 230s intake 240s ex on a 111) and as they always are, it was a breeze and has no buck. That smaller cam though that I first describe has been harder to get the buck out than anything I have messed with... and it's SMALL! Pat G specs cams that make power and he loves those tighter LSAs, but having to tune out buck is something that comes with the territory.

I wonder if it could be ramp rate of the lobes used. I have XFI for intake and XE-R for exhaust. I've heard the same thing about the MS4 and it sucks cuz it's an even bigger cam than mine.
10-25-2009
Frost

You should log throttle follower airflow and have someone ride along. Have them see if that airflow is present during the bucking. Hopefully it will be, that will give you some room to work.
10-26-2009
WS6FirebirdTA00

I believe the bucking has to do with the intake pressure pulsations. I have always found the valve events of the smaller cams can exaggerate this issue. I just put a larger cam in my car and it runs even smoother now chugging around 1400-1600 below 35 MPH.
10-27-2009
jimmypop13

Quote:

Originally Posted by WS6FirebirdTA00

I believe the bucking has to do with the intake pressure pulsations. I have always found the valve events of the smaller cams can exaggerate this issue. I just put a larger cam in my car and it runs even smoother now chugging around 1400-1600 below 35 MPH.

I really like the Polluter cam, do you think it's the right size that it could help? So now you guys have to help me pick 110 or 112 lsa?!
I was thinking I had to go smaller but your answer would explain why Frost had an easy time tuning an MS4 and a hard time tuning a smaller cam.
10-27-2009
WS6FirebirdTA00

If you changed the cam, I would go with something that gave good power across the board (both low end and up top). The cam you have is not a bad cam (I was actually going to go with a similar spec cam). The cams that seem to be real odd balls to me are the 224-230 duration range in various combinations. I would try to tweak out your issues. Make sure you first get the fueling right. You may need to tweak the switch points for the o2 sensors. A lean running car will surge. Sorry if this has been said, I did not read through all the posts. You need the right combination of fueling and timing. It is still possible to go to a new cam and get the surge. If the o2 sensors switching is lazy, it could also cause surge. Incorrect idle airflow, throttle cracker and follower can also hurt when incorrectly setup.
10-27-2009
jimmypop13

Quote:

Originally Posted by WS6FirebirdTA00

If you changed the cam, I would go with something that gave good power across the board (both low end and up top). The cam you have is not a bad cam (I was actually going to go with a similar spec cam). The cams that seem to be real odd balls to me are the 224-230 duration range in various combinations. I would try to tweak out your issues. Make sure you first get the fueling right. You may need to tweak the switch points for the o2 sensors. A lean running car will surge. Sorry if this has been said, I did not read through all the posts. You need the right combination of fueling and timing. It is still possible to go to a new cam and get the surge. If the o2 sensors switching is lazy, it could also cause surge. Incorrect idle airflow, throttle cracker and follower can also hurt when incorrectly setup.

Any cam suggestions then?
My o2's didn't seem to be working right. Even with brand new Bosch o2s, my PLX wideband was reading 16.5 at idle. I went open loop and am now back to 14.6. I've got throttle cracker disabled and I've tried from 13.5 to 14.7 in the bucking spot with no change in the severity. I also found that 22-24* timing was best but it's still pretty bad even there. What I want in a cam is midrange torque. I want a car that's fun to drive with instant power because I havn't even gone to the track in the 2.5 years I've had the car. I've got all the supporting internal mods to run to 7k without a problem too, so basically I want everything in a cam, BUT NO BUCKING

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