PCM Diagnostics & Tuning HP Tuners | Holley | Diablo

fixed some bucking and dipping...

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Old Dec 11, 2005 | 01:57 PM
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Default fixed some bucking and dipping...

I know a few of us had these issues, I posted on HP Tuners as well. Let me know if it works for anyone else.

Well, I turned off the throttle cracker below 40 mph. Set enable to 40, disable 39. When I push the clutch in the rpms drop dead on 900 and dont move a bit, well a little but nothing that you can see the tach swing back and forth.

This also seemed to help my bucking in 3rd and 4th gear at 1600 rpm.I adjusted the cracker airflow in 1600 for 5th gear speeds and it still has to recover slightly. What I think I might do is zero the table out up to 2200 rpm the whole way and see how that does. That, or I will only let it enable above 50 mph. The car drives much nicer now. Only issue I have, which I think it is related to the o2s hanging on decel, is the rpms will sometimes dip to about 500-600. Only really did it when I was off the gas for a long time and letting it slow by coating in gear. Once I push the clutch in it would dip but recover right to 900 rpm. Seem to be fueling related as it is very rich on those cells on me.

I am going to mess wtih the throttle follower airflow values some more to see what I can do with it. I know there were a few out there needing help with this so I wanted to post up.

Mike
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Old Dec 11, 2005 | 02:57 PM
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cant wait to try it out!! lets hope this is the solution
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Old Dec 11, 2005 | 02:58 PM
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damn it!! this is nino btw... using my wife's account. hahaha.
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Old Dec 11, 2005 | 02:59 PM
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now im logged in
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Old Dec 11, 2005 | 03:23 PM
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Originally Posted by WS6FirebirdTA00
Once I push the clutch in it would dip but recover right to 900 rpm. Seem to be fueling related as it is very rich on those cells on me.
If you fix the fueling in those cells, will try to going back to a normal cracker table to see if the swings were caused by a rich condition?
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Old Dec 11, 2005 | 03:31 PM
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In my experience, bucking has nothing to do with iac position, so i don't see how throttle cracker could be related to bucking.
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Old Dec 11, 2005 | 04:14 PM
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I tried changing the cracker table with no help. I did not try to disable below certain MPH/RPM.

Bill
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Old Dec 11, 2005 | 04:23 PM
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Might help up there, but my biggest issue with bucking is slowing down to make a turn and letting the rpms dip down to 1.5K. Thats where it kills me. Im pretty sure I dont take those turns at 40+
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Old Dec 11, 2005 | 04:53 PM
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Originally Posted by P Mack
In my experience, bucking has nothing to do with iac position, so i don't see how throttle cracker could be related to bucking.
if i put my throttle cracker to 2.0 g/sec at 1600 rpm and let off the gas it bucks like a ****. i have some thoughts on why it happens for that but not so much for regular driving while on the gas. all i know is its not there any more. 25-35 mph was bad going down my street and there is still some bucking but not much.

ragtop, i adjusted my tables now to allow the cracker airflow, just zeroed out up to 1600 rpm. this seems to have fixed that problem of the rpms comming down too fast on decel. i am sure if i had the fueling right it wouldnt have happend, but my injectors are a little too big for those low map areas right now so i cant really get it any leaner. but then again its possible it might not be fuel related, looked at my log and it went to 0 iac steps, im thinking the car was like "too much air, close iac all the way" well now that i have cracker airflow 2200+ rpm it doesnt make that move to 0 iac steps on decel. i assume its due to the fact that the car slowly comes down from those high rpms now. but once at 1600 it goes down fast but wont undershoot the mark.
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Old Dec 11, 2005 | 04:54 PM
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Originally Posted by GuitsBoy
Might help up there, but my biggest issue with bucking is slowing down to make a turn and letting the rpms dip down to 1.5K. Thats where it kills me. Im pretty sure I dont take those turns at 40+
that happened to me too, my airflow values were too large in the throttle cracker and that made it buck. waht mph does it happen at? and what are your cracker values there? set it to 0 and try, wont hurt anything. or put your enable speed 5mph higher than the trouble area
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Old Dec 11, 2005 | 04:58 PM
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Originally Posted by Bill Bowling
I tried changing the cracker table with no help. I did not try to disable below certain MPH/RPM.

Bill
Bill, I have tried tons of changes and the best results were zeroing out the cracker.

here is what i have in the car now,

-Enable 10 mph
-Disable 9 mph
-Zeroed cracker out below 10 mph all the way across and from 0-1600 rpm from 0mph down to about 45 mph (cant remember i am in metric)
-leaving the first 4 columns alone in the throttle follower decay in gear, i multiplied the rest of the table by 0.75
-the follower airflow was set to
0.150
0.200
0.250
0.500
0.750
1.000
1.500
2.000
2.500--->2.500
-follower delays were all set to 0

Last edited by WS6FirebirdTA00; Dec 11, 2005 at 05:05 PM.
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Old Dec 11, 2005 | 05:04 PM
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prob simpler if i did this...
Attached Thumbnails fixed some bucking and dipping...-cracker.jpg   fixed some bucking and dipping...-follower-airflow-follower-decay-gear.jpg  
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Old Dec 11, 2005 | 08:10 PM
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Originally Posted by WS6FirebirdTA00
im thinking the car was like "too much air, close iac all the way"
Hmm, I didn't think the IAC had any feedback like that above the throttle cracker enable speed. Are your idle trims negative when they lock at the throttle cracker enable speed?
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Old Dec 11, 2005 | 08:28 PM
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as soon as the car exits the idle limits the idle trims lock. depending on how long the engine has run (mainly a function of oil temp), they will be anywhere from -0.10 to -0.75 g/sec
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Old Dec 11, 2005 | 08:30 PM
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before my latest tunes the would be positive as well, so i dont know why you were wondering what they were, but my issue has been there in both situations
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Old Dec 11, 2005 | 08:46 PM
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Oh, I was talking about where you said your IAC position was going to 0.
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Old Dec 11, 2005 | 09:07 PM
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ook, yeah that was just on high rpm decel, like a downshift. im gonna scan some more to be sure but i think it was just to get the rmps lower faster since i had cracker disabled, but now its enabled for high rpm so i think it shoudl stay fine
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Old Dec 12, 2005 | 11:33 AM
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I'd have to look at some logs, but the only time my IAC has ever gone to zero was when I had the TB blade set screw open too much.

FWIW, when I got my IAC table dialed in, my bucking problem pretty much went away. But this was a big change (i.e. the table being adjusted from stock to account for the FAST 90).
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Old Dec 12, 2005 | 01:55 PM
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yeah my table is dialed in, but i still have issues. drove the car to work this morning and seems fine. i still have some issues but not nearly as bad,esp at low speed or slowing down, those are pretty much fixed. ive got to recheck the ve, idle air, and effecitve aera and make sure they are all alright
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Old Dec 12, 2005 | 02:00 PM
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Whos writeup or method do you use for effective area. Ive never trusted my results even though i keep coming up with the same results.
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