RPM rise/fall during coast down
10-28-2016, 06:22 PM
#1
Pro
Thread Starter
RPM rise/fall during coast down
Gents,
Is it normal for the rpm to rise and fall about 500 revs when clutch in and coasting to a stop? It quits when I come to full stop, resting at about 700-750.
Is it normal for the rpm to rise and fall about 500 revs when clutch in and coasting to a stop? It quits when I come to full stop, resting at about 700-750.
10-28-2016, 09:11 PM
#2
Tech Contributor
10-29-2016, 06:40 PM
#4
Pro
Thread Starter
Talked to Marc Haibeck. He said this is normal with an aluminum flywheel. Only concern is that the engine stalled yesterday a few times while driving before the engine was completely warmed up.. all good apparently.
10-30-2016, 09:38 AM
#5
Le Mans Master
Member Since: Oct 2004
Location: South-central Missouri
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Common for my 90 immediately after installing headers and especially the Al flywheel. Want more? Remove the secondary port throttles!
I'm hoping that someday someone comes up with the magic "pill" that cures that for the 90s (especially). On occasion, in summer especially, I will experience a stall while decelerating, OR the engine will begin missing and struggling to run. A quick blip of the throttle with the clutch depressed and all is well again. Kinda annoying, to be sure. But, after several years now, I've assimilated it to the point of sensing when it might happen and can usually "work around" it.
Downshifting/engine braking solves a lot of the hunting as well as preventing engine stalling. If I sense it is close to stalling as I come to a stop, the clutch depressed and a blip of the throttle is almost always an instant cure - sometimes a couple "blips" of the throttle is necessary when the temps are in that zone where it seems to occur more often.
If it happened all the time, it would be an issue. But, it seems to be limited (mine anyway) to occasionally occuring when the air temp is around 80-85 ºF and I'm in deceleration after some spirited driving. But, then I'm keenly monitoring it - ready to "blip" if it becomes necessary (not always).
For what it is worth, my wife's 91 ZR-1 does NOT display the hunting - far as I can tell. But, then in addition to headers and aluminum FW, her LT5 has Pete's cams too. And, Pete did the tuning, but I stop short of suggesting it's Pete's tuning that makes the difference. IDK.
Just a sometimes nuisance...low on the priorities list (for me).
I'm hoping that someday someone comes up with the magic "pill" that cures that for the 90s (especially). On occasion, in summer especially, I will experience a stall while decelerating, OR the engine will begin missing and struggling to run. A quick blip of the throttle with the clutch depressed and all is well again. Kinda annoying, to be sure. But, after several years now, I've assimilated it to the point of sensing when it might happen and can usually "work around" it.
Downshifting/engine braking solves a lot of the hunting as well as preventing engine stalling. If I sense it is close to stalling as I come to a stop, the clutch depressed and a blip of the throttle is almost always an instant cure - sometimes a couple "blips" of the throttle is necessary when the temps are in that zone where it seems to occur more often.
If it happened all the time, it would be an issue. But, it seems to be limited (mine anyway) to occasionally occuring when the air temp is around 80-85 ºF and I'm in deceleration after some spirited driving. But, then I'm keenly monitoring it - ready to "blip" if it becomes necessary (not always).
For what it is worth, my wife's 91 ZR-1 does NOT display the hunting - far as I can tell. But, then in addition to headers and aluminum FW, her LT5 has Pete's cams too. And, Pete did the tuning, but I stop short of suggesting it's Pete's tuning that makes the difference. IDK.
Just a sometimes nuisance...low on the priorities list (for me).
10-30-2016, 07:14 PM
#6
Pro
Thread Starter
Concur that it is more of a nuisance than a serious issue. Interesting is that outside temps were around 80 degrees when mine stalled, but mine occurs with a "cold" or moderately warm engine.. just wanted to know from the LT-5 community if this was the norm with my setup. Appears it is, so will adjust my driving to accommodate. No big deal.. thanks for the feedback guys!
10-30-2016, 11:54 PM
#7
Le Mans Master
Idle stabilizes at below 5mph because that's the point where Idle SA kicks in. This can be changed in the calibration and you'll want to flatten timing in the Closed Throttle spark table for the low rpm ranges. Same goes for fuel.
Also, there's a thing called Proportinal Gain which kicks in Closed Loop. You'll find that the values used for a stock motor prove to be a bit too much once you start modifying the motor. The LT-5 tends to be an "unstable" motor, meaning that it reacts to input more easily. So the inputs needs to be diminished to "calm it".
IAC controls also help.
Also, there's a thing called Proportinal Gain which kicks in Closed Loop. You'll find that the values used for a stock motor prove to be a bit too much once you start modifying the motor. The LT-5 tends to be an "unstable" motor, meaning that it reacts to input more easily. So the inputs needs to be diminished to "calm it".
IAC controls also help.
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jss06c6 (10-31-2016)
10-31-2016, 08:17 AM
#8
Pro
Thread Starter
Idle stabilizes at below 5mph because that's the point where Idle SA kicks in. This can be changed in the calibration and you'll want to flatten timing in the Closed Throttle spark table for the low rpm ranges. Same goes for fuel.
Also, there's a thing called Proportinal Gain which kicks in Closed Loop. You'll find that the values used for a stock motor prove to be a bit too much once you start modifying the motor. The LT-5 tends to be an "unstable" motor, meaning that it reacts to input more easily. So the inputs needs to be diminished to "calm it".
IAC controls also help.
Also, there's a thing called Proportinal Gain which kicks in Closed Loop. You'll find that the values used for a stock motor prove to be a bit too much once you start modifying the motor. The LT-5 tends to be an "unstable" motor, meaning that it reacts to input more easily. So the inputs needs to be diminished to "calm it".
IAC controls also help.
Going to send you a PM regarding tuning software you recommended. Thanks for all the counsel and help!
Steve
10-31-2016, 09:51 AM
#10
Le Mans Master
First of all, these are not Flash chips. U will need a UV Eraser and then a burner. So of course you would read the chip and save that cal as a copy prior to making changes.
I am not familiar w the Images system. I use TPRT 5.0
with the correct .xdf mask.
I would suggest getting a Moates Ostrich 2.0 prom emulator so you can avoid the whole tune, log, erase, burn etc. Another alternative is to download the calibration then save it using the correct Mask ID, then replace the stock chip w either 27C256 or 29c512 Flash.
Then use the Moates Burn2 to flash it in combination w TPRT.
Again, pay a visit to thirdgen.org. Read the stickies on Tuning 101 in the DIY Prom section to get started.
P.S. Please join the Registry at zr1.net
I am not familiar w the Images system. I use TPRT 5.0
with the correct .xdf mask.
I would suggest getting a Moates Ostrich 2.0 prom emulator so you can avoid the whole tune, log, erase, burn etc. Another alternative is to download the calibration then save it using the correct Mask ID, then replace the stock chip w either 27C256 or 29c512 Flash.
Then use the Moates Burn2 to flash it in combination w TPRT.
Again, pay a visit to thirdgen.org. Read the stickies on Tuning 101 in the DIY Prom section to get started.
P.S. Please join the Registry at zr1.net
Last edited by Dominic Sorresso; 10-31-2016 at 09:53 AM.
10-31-2016, 10:07 AM
#11
Le Mans Master
Glad to provide answers if u have a specific question. The topic of tuning is pretty involved. It is a topic not easily discussed in this type of venue unless you have some initial experience w it. Not trying to be a snob, but it is important to expose yourself to some basic information and terminology.
That's why I always recommend visiting thirdgen.org and reading the excellent tuning primers in the DIY Prom section. Very knowledgeable people on that site. Pretty amazing stuff.
Also let me recommend visiting dynamicefi.com. Another good source of information.
That's why I always recommend visiting thirdgen.org and reading the excellent tuning primers in the DIY Prom section. Very knowledgeable people on that site. Pretty amazing stuff.
Also let me recommend visiting dynamicefi.com. Another good source of information.
11-10-2016, 08:40 PM
#13
Le Mans Master
I have been recently playing w tune to try an subdue or eliminate this issue. It is more pronounced when the motor is modded.
In a previous post I stated something about the Idle SA MPH. That is incorrect. The parameter I should have referred to was the
Min MPH for Throttle Follower. In the stock calibration , that's set at 5mph. You can raise the MPH on this which helps. Also, raising the steps on the Min Throttle Follower to keep idle up helps.
In a previous post I stated something about the Idle SA MPH. That is incorrect. The parameter I should have referred to was the
Min MPH for Throttle Follower. In the stock calibration , that's set at 5mph. You can raise the MPH on this which helps. Also, raising the steps on the Min Throttle Follower to keep idle up helps.
Last edited by Dominic Sorresso; 11-10-2016 at 11:28 PM.
11-14-2016, 07:56 AM
#14
Le Mans Master
I have been recently playing w tune to try an subdue or eliminate this issue. It is more pronounced when the motor is modded.
In a previous post I stated something about the Idle SA MPH. That is incorrect. The parameter I should have referred to was the
Min MPH for Throttle Follower. In the stock calibration , that's set at 5mph. You can raise the MPH on this which helps. Also, raising the steps on the Min Throttle Follower to keep idle up helps.
In a previous post I stated something about the Idle SA MPH. That is incorrect. The parameter I should have referred to was the
Min MPH for Throttle Follower. In the stock calibration , that's set at 5mph. You can raise the MPH on this which helps. Also, raising the steps on the Min Throttle Follower to keep idle up helps.
The LSV would be a good test case with the Stg II cams. Seems like a bit of tuning here is needed with the big cams and this whole "idle step down" thing.
Very interesting info! I'd like to talk to you more about it and do some experimentation as we're tuning the car now. Please PM me your number and we'll talk!
11-17-2016, 12:05 PM
#15
Le Mans Master
The LSV would be a good test case with the Stg II cams. Seems like a bit of tuning here is needed with the big cams and this whole "idle step down" thing.
Very interesting info! I'd like to talk to you more about it and do some experimentation as we're tuning the car now. Please PM me your number and we'll talk!
Very interesting info! I'd like to talk to you more about it and do some experimentation as we're tuning the car now. Please PM me your number and we'll talk!
Respinded via PM
11-20-2016, 05:12 AM
#16
Le Mans Master
Member Since: Oct 2004
Location: South-central Missouri
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This might be a "last resort", but if all else fails, perhaps a simple op-amp could be used to simulate zero mph signal, triggered by the TPS signal at zero throttle, no? Thoughts?