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Thread: When I tune a car that bucks...

  1. #1

    When I tune a car that bucks...

    Where do you look 1st? I have been concerned about this for a while now and I'm pretty sure it has nothing to do with my timing.
    While rolling through a parking lot in 1st gear in the 11-1600rpm range my car bucks like a PBR bronco
    Tonight I went out and tried reducing my timing (which did help a little, especially on decel), + VE and -VE. Nothing would cure it.
    It is very bad when you let off and try to reapply the gas lightly. Again, this is all happening in 1st gear, low rpm.
    I found this post and it seems like it is worth a try but I'm not sure how to accomplish it, any ideas?

    " Looks like the surging is in line with the oscillation of the O2 sensors to me. Disable closed loop and run open loop up till 1600RPM. Use the VE table to smooth out fuel transitions so that your injector PWM remains constant.

    Should fix it...

    Likely you will need to lean her out a fair bit."

    Thanks guys.
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  2. #2
    Senior Tuner Russ K's Avatar
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    I have a 229/242/.630/114 camshaft, and it has a slight surge at light throttle low rpm. I've tried open loop & changing the AFR & spark with the VCM controls while a friend drove the car. You can make the surge better or worse, but not eliminate it. My car just runs best in closed loop. A cam like yours will have some surge no matter how its tuned. You can get the spark timing & the LTFT map & rpm boundary tables to match your cam.
    This will help some.

    Russ Kemp
    Last edited by Russ K; 05-14-2007 at 12:58 AM.

  3. #3
    Quote Originally Posted by Russ K
    I have a 229/242/.630/114 camshaft, and it has a slight surge at light throttle low rpm. I've tried open loop & changing the AFR & spark with the VCM controls while a friend drove the car. You can make the surge better or worse, but not eliminate it. My car just runs best in closed loop. A cam like yours will have some surge no matter how its tuned. You can get the spark timing & the LTFT map & rpm boundary tables to match your cam.
    This will help some.

    Russ Kemp
    Just for comparison sakes I see the same issue on any cam above ~220s and ~0.550" lift and was just curious what sort of MAP it occurs at in your case. I personally find higher vacuum than idle (ie low MAP) around the 1200-1500 rpm where it will occur, after this cam efficiency improves enough to it does not occur. I figure overlap or reversion is at play here but I am clinging onto hope that I can minimise as much as possible.

    The best solution I have found to date is to re-locate the IAT to give a true indication of IAT (as due heatsoak makes the PCM pull unnecessary fuel) and then a combination of advice from yourself and EC_Tune which is to get as close as possible with the WB and then use the NBs to fine tune steady state throttle 1000rpm to 2400rpm 25kPa to 70kPa and this has helped me enormously, but still not completely erradicated it. Too rich and it will occur as will too lean as close as possible to stoich (in mild cams at least for me) seems to be the go. I cannot remember where I heard it but I was never given truer advice than, 'mate, it will never drive like a stocker because it isn't a stocker'.

  4. #4
    Thanks for the responses.

    Russ, how would I go about LTFT Map and rpm boundries to match my cam and how can I tell that they don't match right now?

    I am running the 1 barSD system currently so it can't be reversion in my case.

    BTW, that's a much bigger cam than you were running last time we spoke.
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  5. #5
    Senior Tuner Frost's Avatar
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    Quote Originally Posted by SSUte01
    Just for comparison sakes I see the same issue on any cam above ~220s and ~0.550" lift and was just curious what sort of MAP it occurs at in your case. I personally find higher vacuum than idle (ie low MAP) around the 1200-1500 rpm where it will occur, after this cam efficiency improves enough to it does not occur. I figure overlap or reversion is at play here but I am clinging onto hope that I can minimise as much as possible.

    The best solution I have found to date is to re-locate the IAT to give a true indication of IAT (as due heatsoak makes the PCM pull unnecessary fuel) and then a combination of advice from yourself and EC_Tune which is to get as close as possible with the WB and then use the NBs to fine tune steady state throttle 1000rpm to 2400rpm 25kPa to 70kPa and this has helped me enormously, but still not completely erradicated it. Too rich and it will occur as will too lean as close as possible to stoich (in mild cams at least for me) seems to be the go. I cannot remember where I heard it but I was never given truer advice than, 'mate, it will never drive like a stocker because it isn't a stocker'.

    Outside of getting the fueling nailed like you mention, which helps, I seem to get better results with substantially lower-than-stock timing up to about 2K RPMs...
    Steve Williams
    TunedbyFrost.com


  6. #6
    Quote Originally Posted by Frost
    Outside of getting the fueling nailed like you mention, which helps, I seem to get better results with substantially lower-than-stock timing up to about 2K RPMs...
    I have seen this before also. A forum member has an identical set-up with the exception of a slightly larger cam and his timing is almost 50% lower than stock in the 1-2k zone. He is running a true OLSD tune though.
    Keep the ideas coming guys, I know there are other guys out there whose fillings are coming loose from low rpm surging.
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  7. #7
    Tuner miami993c297's Avatar
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    Quote Originally Posted by 02Z0h6
    I have seen this before also. A forum member has an identical set-up with the exception of a slightly larger cam and his timing is almost 50% lower than stock in the 1-2k zone. He is running a true OLSD tune though.
    Keep the ideas coming guys, I know there are other guys out there whose fillings are coming loose from low rpm surging.
    Here it is, last log attached.

    Strange timing...maybe...BUT working with my set-up.

    Christian


    418Ci TEC Assembled/ ETP-FTI Prep/ FTI "Barbara Streisand" Cam 664 HP Pump Gas.
    Losers can always explain why...as winners never explain how...
    What makes a Top Performer Human is the mistake…What makes him the greatest is his ability to repair it

  8. #8
    Quote Originally Posted by miami993c297
    Here it is, last log attached.

    Strange timing...maybe...BUT working with my set-up.

    Christian

    Christian, how are u? It's Chad from the Corvetteforum. You were the one I was referring to in my previous post. Thanks for posting up your tune!
    Lowering my timing did help in low rpm-low-load areas did help but I only went to about 18*. I may try to go a little lower next time.
    I do have a real problem when letting off and re-applying the gas lightly. The car will buck violently. The transistion between the two causes major bucking.
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  9. #9
    Tuner miami993c297's Avatar
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    Quote Originally Posted by 02Z0h6
    Christian, how are u? It's Chad from the Corvetteforum. You were the one I was referring to in my previous post. Thanks for posting up your tune!
    Lowering my timing did help in low rpm-low-load areas did help but I only went to about 18*. I may try to go a little lower next time.
    I do have a real problem when letting off and re-applying the gas lightly. The car will buck violently. The transistion between the two causes major bucking.

    Hi Chad,

    Glad you made some progress with your Engine-Combo / Tune-Setting...

    Take a close look to my log in the previous post, the timing in some areas is pretty low...for some reasons.

    Sometime between 15° and 17° there is a huge differents in certain spots.

    Christian


    418Ci TEC Assembled/ ETP-FTI Prep/ FTI "Barbara Streisand" Cam 664 HP Pump Gas.
    Losers can always explain why...as winners never explain how...
    What makes a Top Performer Human is the mistake…What makes him the greatest is his ability to repair it

  10. #10
    Tuner in Training
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    I've been screwing around with the same issue for 5-6 months now. Tried OL for low rpm, timing, VE adjustments, proportional fueling,.............

    I got mine running better (not perfect) by BOOSTING the timing and lowering the idle. Greg Ganish recommended to me when I took his class.

    Its back to acting up a little since I put in the SVO 30's last weekend, but I'm not through tuning that yet. So its actually pretty well behaved now.

    I've attached tune if you wanna look.

    Dick
    Dick

    04 CM C5 vert
    AFR205, G5X3, LGLT Street, Corsa, Blackwing
    rwhp 404@6800, rwtq 357@53000rpm (so far)
    on a Mustang Dyno
    (25 more ponies left on the table. HPTuners gonna get me there)
    17 Z06 - stock
    19 Ford F-150, 62 corvette stock

  11. #11
    Try enabling your MAF and correcting for it, this helped me tons.

    My SOM T/A's FQuick!
    2002 T/A: Torquer V3, Full Boltons, Suspension, M6, Lots of misc things.
    My Z/28's Cardomain (13.9 @ 101.1)
    1997 Z/28: A4, Some boltons, Lots of misc things.

  12. #12
    Senior Tuner Russ K's Avatar
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    Quote Originally Posted by 02Z0h6
    Thanks for the responses.

    Russ, how would I go about LTFT Map and rpm boundries to match my cam and how can I tell that they don't match right now?

    I am running the 1 barSD system currently so it can't be reversion in my case.

    BTW, that's a much bigger cam than you were running last time we spoke.
    The low rpm boundary has to be ~100 rpm higher than your idle speed, then raise the high rpm to 2400, then have the mid rpm half way between. The low map boundary should be ~5 kpa higher than your idle map (in gear for an A4), then the high map should be 80-85 kpa, and the mid map half way between. These settings will enable all the fuel trim cells. This is because your idle rpm & map is higher than stock, so the low rpm & map fuel trim cells will be out of bounds and not used.

    Yeah, the new cam, ported LPE heads, speed pro pistons & file fit rings really woke the car up!

    Russ Kemp

  13. #13
    Quote Originally Posted by Russ K
    The low rpm boundary has to be ~100 rpm higher than your idle speed, then raise the high rpm to 2400, then have the mid rpm half way between. The low map boundary should be ~5 kpa higher than your idle map (in gear for an A4), then the high map should be 80-85 kpa, and the mid map half way between. These settings will enable all the fuel trim cells. This is because your idle rpm & map is higher than stock, so the low rpm & map fuel trim cells will be out of bounds and not used.

    Yeah, the new cam, ported LPE heads, speed pro pistons & file fit rings really woke the car up!

    Russ Kemp
    Thanks Russ. I'm looking under Airflow>Dynamic Airflow>>Zone RPM boundaries and Zone MAP boundaries. Is that correct? If so, they read

    RPM Zone 0-1 1000rpm (my car idles at 950) 45-55kpa I believe
    RPM Zone 1-2 2000rpm
    RPM Zone 2-3 3000rpm

    I need to go through the help file a little more tomorrow Russ. It's pretty late.

    Thanks to all who responded today and posted up there tunes for me to look at.
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  14. #14
    Senior Tuner Russ K's Avatar
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    These are the tables you need to set up.

    Russ Kemp

  15. #15
    Quote Originally Posted by Russ K
    These are the tables you need to set up.

    Russ Kemp
    Excellent. Thanks Russ.

    Any numbers with the new set-up? What size injector are you running?
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  16. #16
    Senior Tuner Russ K's Avatar
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    Stock injectors @ 93% duty cycle. This is with a 13.0 AFR, no numbers yet. I'm planning on a trip to the dyno in Calgary in June.

    Russ Kemp

  17. #17
    Back from the dead. I went out tonight and tried a couple things with RTT. I tried using much lower timing values in low load/rpm cells which seemed to help marginally. I also tried pulling fuel in those areas as well as adding. Car didn't really like pulling fuel and adding seemed to help a little. Bottom line is I don't feel any further ahead. Mods are in sig and running 1-bar SD. I may try to re-enable the maf and see what happens.
    I attached a 5-min 1st gear ride through a parking lot and my current tune. My timing seems to be all over the place when the car starts to buck. It looks like a sawblade on the histo. I'm not sure what's causing it though. It seems the transition from coasting very slowly to light throttle throws everything into a frenzy.
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  18. #18
    Like I mentioned above I have tried a large number of combos and to cure it in mine and I mean so I cannot get any surging or bucking ,bear in mind I shouldn't have had it in the first case as my cam is only 218/224 114 LSA 0.521/0.521 but I added 1.8 RR which made lift ~0.550 and created this problem I haven't had on my vehicle only others that I have looked at.

    - Followed Doug and Russ' advice indirectly about nailling fuelling by both WB and NB where appropriate.

    - Tried Frost's advice about lowering timing,gradually did this until way less than stock and made problem terrible in mine but has helped in others

    - Used Scanner and commanded really high timing and worked back from like 50* and this in combination with fuelling in this small cam cured it - like I said it was due untuned that it even existed in the first place. For whatever reason I cannot get higher than 40* timing regarless of what I command (noone could figure this out on an earlier thread) in the Editor but can get enormous amount of advance in Scanner hence 50* and worked back. Since 40 was my limit that is what my timing is in trouble area and now no issue at all.

    I guess there are physical/mechanical limits but trying to minimise the effects through tuning in a M6 can be long and tedious. I like to nail fuelling to stoich and then use timing at extremes and work back real time using scanner until I minimise or remove the issue

    Probably not applicable to you guys with mild and bigger cams but that is what worked for me.


  19. #19
    Thanks for thresponse SS. As far as fueling goes I do have a WB hooked up but was not logging, just watching when the car starts to buck. Nothing really unusual. Car is trying to maintain stoich and hovers around 14.2-14.7. I have this issue with my LM-1 display not corresponding with my scanner. They seem to be off about .3-.4 afr at all times. I did not try to add timing as I've had people tell me it's already high in those areas so I decided to back it off from there.
    How long should I give the car after making ve changes to respond and adjust during RTT?
    ETP 215's 60cc
    TR223/234 .636/.599 114lsa
    Fast90/NW90TB
    All bolt-ons -ewp

  20. #20
    Tuner miami993c297's Avatar
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    Quote Originally Posted by 02Z0h6
    Thanks for thresponse SS. As far as fueling goes I do have a WB hooked up but was not logging, just watching when the car starts to buck. Nothing really unusual. Car is trying to maintain stoich and hovers around 14.2-14.7. I have this issue with my LM-1 display not corresponding with my scanner. They seem to be off about .3-.4 afr at all times. I did not try to add timing as I've had people tell me it's already high in those areas so I decided to back it off from there.
    How long should I give the car after making ve changes to respond and adjust during RTT?
    Hi Chad,

    I would try to enriching the zone where the problem exist to the ~13.4/13.7 AFR value...

    Try it when you have a chance and report back.

    Christian


    418Ci TEC Assembled/ ETP-FTI Prep/ FTI "Barbara Streisand" Cam 664 HP Pump Gas.
    Losers can always explain why...as winners never explain how...
    What makes a Top Performer Human is the mistake…What makes him the greatest is his ability to repair it