Timing fluctuation = bucking @ no/low throttle
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From: Port Tobacco, MD
Timing fluctuation = bucking @ no/low throttle Today I was driving the car with the logger on and tried to figure out what causes the car to surge @ idle and low Throttle position, it seems as if when you get to low TPS the timing switches from the main table to the park or drive table. Anyone confirm this? The timing looks like it is jumping from the main table to the park table.
Phil
Phil
Wait4me talks about this in this thread.
https://ls1tech.com/forums/pcm-diagnostics-tuning/540073-idle-spark-advance.html
I changed my high/low octane timing tables to read the same as my idle tables in the pertinant cells and it helped me alot.
https://ls1tech.com/forums/pcm-diagnostics-tuning/540073-idle-spark-advance.html
I changed my high/low octane timing tables to read the same as my idle tables in the pertinant cells and it helped me alot.
I'd like to here more about how the throttle cracker would help. Mine is much better than it was but it still there enough that I know that it isn't right yet. With all of these damn tables and some of the stories of the gigantic cams running "buck-free", Someone please share the magic.
I noticed I have a very noticable bucking when I let off the gas at about 60 and coast to a stop while in OL mode.
If I got back to normal CL mode, it is almost completly gone.
Going from OL to CL my AFR error % doesn't change for than -1/+1% so I don't believe its a fuel issue.
If I got back to normal CL mode, it is almost completly gone.
Going from OL to CL my AFR error % doesn't change for than -1/+1% so I don't believe its a fuel issue.
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Another approach to your tuning issues are to mess with tables : B5935 and B5936.
What these tables do is let the computer do all the work for us on idle correction. If you have ever noticed why the timing jumps all over the place when surging is because of these tables. So, the fix? Well, by making those tables more accurate to the needs of your application will make the vehicle alot smoother running. Every cam is different though so you just need to play with those numbers to make it right.
By using the base tables though, you are just bringing up the spark "Center" for it to use those idle spark correction tables. So it is good to hit the center sweet spot on the timing values you choose. Usually 26 degrees is a good number for idling on the base and main timing tables.
What these tables do is let the computer do all the work for us on idle correction. If you have ever noticed why the timing jumps all over the place when surging is because of these tables. So, the fix? Well, by making those tables more accurate to the needs of your application will make the vehicle alot smoother running. Every cam is different though so you just need to play with those numbers to make it right.
By using the base tables though, you are just bringing up the spark "Center" for it to use those idle spark correction tables. So it is good to hit the center sweet spot on the timing values you choose. Usually 26 degrees is a good number for idling on the base and main timing tables.
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Verdad Gallardo wait4me - I assume that phil99vette is having the same issue as me... Idle is fine. My idle is rock solid at 800 rpm, @ 55 KPA.
It's right above idle where the bucking accours. For instance, lets say:
RPM: 1200 - 1800
MAP: 35 - 55 KPA
TPA: 0% - 5%
This happens while decelerating or maintaining low rpm speed like driving through a parking lot or making a right hand turn at a light. It also happens while maintaining or decelerating at highway speeds in the same RPM range.
While Im sure that it does fluctuate between high octane and base spark tables, I dont know that it would be using the overspeed / underspeed correction since its not shooting for a target idle speed. I have mirrored my main and base tables but this hasnt eliminated it. The best luck ive had was running my base spark tables rediculously high just past idle. 28* @ 800 rpm, 42* @ 1200 rpm, 46* @ 1600 rpm, for the top five rows.
It's right above idle where the bucking accours. For instance, lets say:
RPM: 1200 - 1800
MAP: 35 - 55 KPA
TPA: 0% - 5%
This happens while decelerating or maintaining low rpm speed like driving through a parking lot or making a right hand turn at a light. It also happens while maintaining or decelerating at highway speeds in the same RPM range.
While Im sure that it does fluctuate between high octane and base spark tables, I dont know that it would be using the overspeed / underspeed correction since its not shooting for a target idle speed. I have mirrored my main and base tables but this hasnt eliminated it. The best luck ive had was running my base spark tables rediculously high just past idle. 28* @ 800 rpm, 42* @ 1200 rpm, 46* @ 1600 rpm, for the top five rows.
I think the main thing is, you want to eliminate
any discrepancies between the idle and main
spark tables, in regions where they overlap or
abut. That way if you are bumping across some
decision boundary, it doesn't matter because
the data is the same wherever you look.
any discrepancies between the idle and main
spark tables, in regions where they overlap or
abut. That way if you are bumping across some
decision boundary, it doesn't matter because
the data is the same wherever you look.
Originally Posted by jimmyblue
I think the main thing is, you want to eliminate
any discrepancies between the idle and main
spark tables, in regions where they overlap or
abut. That way if you are bumping across some
decision boundary, it doesn't matter because
the data is the same wherever you look.
any discrepancies between the idle and main
spark tables, in regions where they overlap or
abut. That way if you are bumping across some
decision boundary, it doesn't matter because
the data is the same wherever you look.
Everybody has a different view on how to aleviate bucking, some say throw timing at it, other take it away, some throw fuel at it. And like it was alrady mentioned, some people install their mammoth bumpsticks and they just seem to drive perfectly out of the box.
Guits,
I am having the same exact problem as you. I have also got all my timing tables looking the same. I have also made sure that all of the cells that surround my "problem cells" are identical in the timing tables as well. My main problem cells are 1600RPM and 1800RPM @ .24 g/cyl. I am at 36* right now in these cells. They dont jump around either. While in 4th gear I can hit either of these cells solid and get the bucking. I just took it out for a log run and tried to adding a couple of degrees of timing ( to 36 ) to see if that helped. It didn't help but it did throw off my VE in corresponding cells (+2). My other problem is that I run in OLSD and I can't just pull over and make changes and log because I have the warm start lean issue so I have to drive around until that clears up before I can get an accurate log. What a pain in the ***! Now I have to fix the fuel and log again. Then I can give it more timing. Drive till lean start clears. Log. Fix VE. rinse and repeat. I hope that I can clear it up. I should note that I had the same problem with the slightly larger reverse split cam that I had in the car before. Still interested in a step by step on the throttle cracker to see if that helps. The problem exists while deccelerating (DFCO is off) and while holding at low throttle. Basically, whenever I get into those cells I mentioned above.
I am having the same exact problem as you. I have also got all my timing tables looking the same. I have also made sure that all of the cells that surround my "problem cells" are identical in the timing tables as well. My main problem cells are 1600RPM and 1800RPM @ .24 g/cyl. I am at 36* right now in these cells. They dont jump around either. While in 4th gear I can hit either of these cells solid and get the bucking. I just took it out for a log run and tried to adding a couple of degrees of timing ( to 36 ) to see if that helped. It didn't help but it did throw off my VE in corresponding cells (+2). My other problem is that I run in OLSD and I can't just pull over and make changes and log because I have the warm start lean issue so I have to drive around until that clears up before I can get an accurate log. What a pain in the ***! Now I have to fix the fuel and log again. Then I can give it more timing. Drive till lean start clears. Log. Fix VE. rinse and repeat. I hope that I can clear it up. I should note that I had the same problem with the slightly larger reverse split cam that I had in the car before. Still interested in a step by step on the throttle cracker to see if that helps. The problem exists while deccelerating (DFCO is off) and while holding at low throttle. Basically, whenever I get into those cells I mentioned above.
Did running the timing at 42-46 clear it completely? What mods do you have? What size cam? Are you still running the timing that high? Did it knock? I am desperate to get the bucking gone.
CobraKiller -
My bucking occours a lot lower than 28 g/s. Mines mostly in the top 3 rows. I tend to richen it up to 14.0 - 14.4 AFR in the bucking areas too. Im running the real high timeing more in the base spark tables. The high octane tables are more of a constant slope. I have no KR in the high timing cells. Just a little bit occasionally at part throttle or lugging. The extra timing and fuel has certainly helped out quite a bit, but its still there a little bit. Also, I found that running OL/MAF was a little more consistant than OL/SD.
If I come across any profound remedies for bucking, ill be sure to shout the info from the rooftops.
Oh, and Mods are in sig above, but here it is again...
My bucking occours a lot lower than 28 g/s. Mines mostly in the top 3 rows. I tend to richen it up to 14.0 - 14.4 AFR in the bucking areas too. Im running the real high timeing more in the base spark tables. The high octane tables are more of a constant slope. I have no KR in the high timing cells. Just a little bit occasionally at part throttle or lugging. The extra timing and fuel has certainly helped out quite a bit, but its still there a little bit. Also, I found that running OL/MAF was a little more consistant than OL/SD.
If I come across any profound remedies for bucking, ill be sure to shout the info from the rooftops.
Oh, and Mods are in sig above, but here it is again...
Originally Posted by 98Z28CobraKiller
What plugs are you running?
11.0:1 SCR
8.4 DCR
.047" quench
Take a look at http://www.web-srv.com/~tony/tuning/current/ for my current .hpt
Originally Posted by Phil99vette
If your getting surge than I'd be willin to bet your timing is jumping around. My timing doesnt jump now and I don't get surge with a small 254/260.