Bucking between 1000 to 2000 RPM, How do I tune it out?
03-29-2008, 02:22 PM
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Bucking between 1000 to 2000 RPM, How do I tune it out? I have done a search on bucking, and the threads all say that its in the tune. Nobody gives a method of tuning it out. Couple years back, I remember someone said to reduce the timing advance in that RPM range.
What is the latest on this issue, how do I elimenate or reduce the bucking? I have been throwing several tunes onto the PCM since I installed an LS2 402 short block. I have had the engine running for about two weeks now. The car is running fairly well right now, but I still got a ways to go, and I really need to do something about the bucking.
Please help. Please see my sig for cam specs.
What is the latest on this issue, how do I elimenate or reduce the bucking? I have been throwing several tunes onto the PCM since I installed an LS2 402 short block. I have had the engine running for about two weeks now. The car is running fairly well right now, but I still got a ways to go, and I really need to do something about the bucking.
Please help. Please see my sig for cam specs.
03-29-2008, 02:46 PM
#2
start by setting the throttle cracker to 0 everywhere you have bucking except 400 RPMs and see how far that takes you. If it's already zero, begin reducing your idle airflow table; it's always offsetting the IAC.
Last edited by Frost; 03-29-2008 at 11:17 PM.
03-29-2008, 04:38 PM
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From my experiences working with a 420ci SB2.2 platform (268/278, .800 gross valve lift / 13:1) verify your fueling is consistent (no large changes between RPM break points) and use additional spark advance.
03-29-2008, 07:29 PM
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The school-zone bucking is one I fought for a while. Turned out to be a combo of AFR, spark, and IAC control. There was no silver bullet tuning this either. The biggest help I had was using the Road Runner PCM to make changes on the fly.
Address each one of these areas individually. If you start adjusting all three, you'll be chasing your tail. Make small steps. i.e. +- 0.1 until you achieve no further improvement adjusting that table. Wash-rinse-repeat. You will eventually line out the tune and realize stock like manners.
Address each one of these areas individually. If you start adjusting all three, you'll be chasing your tail. Make small steps. i.e. +- 0.1 until you achieve no further improvement adjusting that table. Wash-rinse-repeat. You will eventually line out the tune and realize stock like manners.
03-29-2008, 11:09 PM
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Thank you for the replies. Fortunately, I will be able to try these fixes tomorrow,,, we should get dry weather instead of the rain that was predicted earlier.
03-30-2008, 05:56 PM
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I have taken 2* out of the timing (borders are 0 to .32 gms/sec and 400 to 1800 RPM). This seemed like it made the bucking slightly worse. Then I added 4* back in, so I am 2* advanced from before. This change seemed to help a little, but the car still bucks pretty bad. Since I am running in closed loop, I cant alter the AFR. Apart from timing, what can I tune to elimenate this bucking? I see that IAC control is mentioned above. My IAC is running about 45 at idle, and maybe 50 to 60 while in 3rd gear at 1600 RPM when the bucking is at its worse.
03-30-2008, 07:21 PM
#7
it really sounds like an airflow problem.... did you try what I posted? Your throttle cracker (99, m6, the table is different by years/trans) adds 1.5g through most of the area you describe. For a test, take it all out over 400 RPMs up to 2200 and see how it goes.
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03-30-2008, 07:40 PM
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randy: About same for you, I dont know what an "auto VE tune" is. I am running a MAF and MAP, I have never run a MAP (speed density) tune only. I will do a search for this item.
03-31-2008, 06:26 PM
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Slowhawk: Yes, the timing is jumping around not 15 degrees, but in the 5 to 10 degree range when the car bucks.
So, if I were to out 40 degrees of timing in all timing cells between the boundaries of 1000 to 1800 RPM and 0.08 to 0.32 gms/cyl, would this help? I would say yes. Too bad is thunderstoming this evening here.
What would be a good average timing advance in my bucking zone?
So, if I were to out 40 degrees of timing in all timing cells between the boundaries of 1000 to 1800 RPM and 0.08 to 0.32 gms/cyl, would this help? I would say yes. Too bad is thunderstoming this evening here.
What would be a good average timing advance in my bucking zone?
04-01-2008, 11:34 AM
#16
That's "throttle cracker". I don't know where it is at, but you need to find out what it is called in your suite and look here. I only move to timing changes AFTER getting airflow right, because too much airflow causes this to happen worse than timing.
Post your .bin file here, attach it to a post in this thread, and I will edit it here and re-post it in the thread for you to try.
04-01-2008, 05:51 PM
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I put all cells at off-idle to 38* (not 40),,, this elimenated about 2/3 of the bucking. So a SUCCESS! For some reason ATAP was logging 36* when it should have been 38*. Is there another table that will be taking timing out? The KR was = 0.
Most of the time I was in FTC 6, and the LTFTs were a solid 2.3% and -0.8% (no changing, the PCM fully learned FTC 6). Therefore, the fueling should have been fairly consistant. The PW on both banks was 3 msec.
What else might help with bucking? (other than drive faster!)
Most of the time I was in FTC 6, and the LTFTs were a solid 2.3% and -0.8% (no changing, the PCM fully learned FTC 6). Therefore, the fueling should have been fairly consistant. The PW on both banks was 3 msec.
What else might help with bucking? (other than drive faster!)
04-01-2008, 05:58 PM
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Frost: I am using LS1Edit, the extensions are .LS1....
I dont know if this will work.
EDIT: Ok i dont know how to upload, i can do it on 3rdgen but not here, what bullshit!
I dont know if this will work.
EDIT: Ok i dont know how to upload, i can do it on 3rdgen but not here, what bullshit!
Last edited by Doc99SS; 04-01-2008 at 07:10 PM.
04-01-2008, 09:39 PM
#20
I thought they were .bin (a binary)
Oh well, glad the timing helped get rid of some of it. Usually the most help I get from timing (other than getting it stable as was noted) comes from taking a good bit out.
I'm not even sure whether or not Edit has access to the throttle cracker table to be honest, but it's routinely where I get rid of bucking after the AFR is good and timing is as well.
Oh well, glad the timing helped get rid of some of it. Usually the most help I get from timing (other than getting it stable as was noted) comes from taking a good bit out.
I'm not even sure whether or not Edit has access to the throttle cracker table to be honest, but it's routinely where I get rid of bucking after the AFR is good and timing is as well.