Rpm hang/overshoot when downshifting and coming to a stop
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Rpm hang/overshoot when downshifting and coming to a stop
Fbody A4 car with h/c/i
Car idles perfect, nearly got the whole RAF dialed in with the idle config histogram (It doesn't get cold enough in TX to dial in the far left)
drives perfect, Races Perfect. The only problem i have is the (ughhhh....ughhhhhh....) the RPMs do coming to a stop. It doesn't do it as bad when the car is warmed up but when its cold it does it horribly. I do not know what could be causing it. Im running SD enhanced OS as well.. I've made a few changes in real time tuning seeing if it would help (underspeed/overspeed/throttle follower/throttle cracker) It just pisses me off how great i've gotten the car to perform but I can't dial in that coasting idle or coming to a stop etc. I'll post a copy of my tune and see what you guys think.. I'm looking to learn how to do this on my own.. Not just a "here, try this" I wanna know why the car is doing this and what i should do to fix it..
Car idles perfect, nearly got the whole RAF dialed in with the idle config histogram (It doesn't get cold enough in TX to dial in the far left)
drives perfect, Races Perfect. The only problem i have is the (ughhhh....ughhhhhh....) the RPMs do coming to a stop. It doesn't do it as bad when the car is warmed up but when its cold it does it horribly. I do not know what could be causing it. Im running SD enhanced OS as well.. I've made a few changes in real time tuning seeing if it would help (underspeed/overspeed/throttle follower/throttle cracker) It just pisses me off how great i've gotten the car to perform but I can't dial in that coasting idle or coming to a stop etc. I'll post a copy of my tune and see what you guys think.. I'm looking to learn how to do this on my own.. Not just a "here, try this" I wanna know why the car is doing this and what i should do to fix it..
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i did a few changes and the problem is less now. Still does it though. heres a log from today when i went to meet someone
ignore the Wideband in the scan, I screwed up my inputs when i made a seperate config for my NGK wideband (car has PLX afr mounted)
ignore the Wideband in the scan, I screwed up my inputs when i made a seperate config for my NGK wideband (car has PLX afr mounted)
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Aside from the follower usual I also needed to:
Inflate the cooler temp areas of the RAF by 1-2g and let the stit worry about pulling air as needed.
Raise the timing table at 800 by 4* and 400 by 8*. Kind of a catch so you don't loose brake boost.
The low speed areas of the follower are VERY sensitive. Little to much it hangs too little it dies.
Inflate the cooler temp areas of the RAF by 1-2g and let the stit worry about pulling air as needed.
Raise the timing table at 800 by 4* and 400 by 8*. Kind of a catch so you don't loose brake boost.
The low speed areas of the follower are VERY sensitive. Little to much it hangs too little it dies.
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zeroe'd out the cracker table and the problem is very minimal now, still hanging a bit with a slight bit of overshoot. what are some average over and underspeed spark values i should be trying? other cammed cars i've messed with do not do this or are as needy lol
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Sounds like you still need to play with the throttle follower. The lower the delay the sooner the decay starts, the higher the decay the faster the follower closes. Try to shorten the delay. Then you may try increasing the decay which will make the IAC/Follower close faster.
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Using my idle .cfg file (Just change it to a .cfg as I can't upload a .cfg file here), do a cold start scan in park till operating temp. Don't touch the throttle or move the car while scanning. Then copy the #1 idle desired histogram into your RAF table of your tune, making sure the units match. Then in compare mode with a stock tune, make the differences the same for the temp cells you didn't hit while scanning.
What are your cam/engine/trans/gear ratio specs?
Russ Kemp
What are your cam/engine/trans/gear ratio specs?
Russ Kemp
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Using my idle .cfg file (Just change it to a .cfg as I can't upload a .cfg file here), do a cold start scan in park till operating temp. Don't touch the throttle or move the car while scanning. Then copy the #1 idle desired histogram into your RAF table of your tune, making sure the units match. Then in compare mode with a stock tune, make the differences the same for the temp cells you didn't hit while scanning.
What are your cam/engine/trans/gear ratio specs?
Russ Kemp
What are your cam/engine/trans/gear ratio specs?
Russ Kemp
#16
I found a tidbit that has helped me with my ac on and hot start which also affects that scenario.
When cammed and both ve and maf tables are all dialed in correctly the base running airflow vs ect needs to be adjusted a lot for bigger duration cams.
Basically when you slow below 3 mph, it uses base running airflow to idle. Think of it this way, you are on the brake and the throttle is shut and you are relying on the IAC to feed it air, except the values its deriving from are stock hence you are starving the engine of air.
If you play with the throttle cracker, you are keeping it in adaptive a bit longer which is fine as well, but the underlying problem is the transition back to base running airflow which is wrong to begin with.
When cammed and both ve and maf tables are all dialed in correctly the base running airflow vs ect needs to be adjusted a lot for bigger duration cams.
Basically when you slow below 3 mph, it uses base running airflow to idle. Think of it this way, you are on the brake and the throttle is shut and you are relying on the IAC to feed it air, except the values its deriving from are stock hence you are starving the engine of air.
If you play with the throttle cracker, you are keeping it in adaptive a bit longer which is fine as well, but the underlying problem is the transition back to base running airflow which is wrong to begin with.
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For some reason, If I use the Russ K idle config, and paste the numbers into my RAF table, my car has a hard time starting and I have to add more air. It gets it close but I have to bump the numbers up a bit to get it to start better.
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fixed this issue a while back.. actually a long *** time ago lol
Car is on OLSD still, was rocking OLMAF for a while till i cracked the maf on a nitrous pass.
lowered my throttle follower values like stated above. no hang, instantly goes to idle after free revs
I raised my Throttle Cracker to 35mph (Lopes like a som' bitch just coasting, I love it)
Zero'd cracker pretty much to 35mph.. Played with over/underspeed spark tables.. over starts at -4 and slopes up to -8.. Under is commanding 8 all across. Spark in park and drive is 19*... Car drives as smooth as ever. only problem is the cold start surging still, I figure some RAF fine tuning will take care of that however
Car is on OLSD still, was rocking OLMAF for a while till i cracked the maf on a nitrous pass.
lowered my throttle follower values like stated above. no hang, instantly goes to idle after free revs
I raised my Throttle Cracker to 35mph (Lopes like a som' bitch just coasting, I love it)
Zero'd cracker pretty much to 35mph.. Played with over/underspeed spark tables.. over starts at -4 and slopes up to -8.. Under is commanding 8 all across. Spark in park and drive is 19*... Car drives as smooth as ever. only problem is the cold start surging still, I figure some RAF fine tuning will take care of that however