coast down to idle issue
10-25-2016, 12:33 PM
#1
7th Gear
Thread Starter
coast down to idle issue
Recently had a well known performance shop (In business for at least 20 years) install a Stage II ProCharger System on my 2003 C5 6 speed corvette and they are having problems tuning the vehicle.
Vehicle:
- 2003 LS1 engine stock modified with a Stage II ProCharger System P-1SC-1 head unit with 8 rib upgrade
- ARH long tube headers with x-pipe and Corsa exhaust
- Fuel system upgraded (fuel pump & injectors) to support ProCharger system
- McLeod RST twin disk clutch with aluminum flywheel
The problem is that when driving the vehicle say 2500 rpm if you push in the clutch coming up to a stop, the vehicle's RPMs go down to say 1000 RPM briefly and then about 4 seconds later fall to around 500 and then back up to 1000. Once it starts, this will cycle for the entire time the vehicle is moving. When the vehicle finally comes to a complete stop it idles correctly around 600 RPM.
Does anyone have any clues I can give them to help solve this problem??
Vehicle:
- 2003 LS1 engine stock modified with a Stage II ProCharger System P-1SC-1 head unit with 8 rib upgrade
- ARH long tube headers with x-pipe and Corsa exhaust
- Fuel system upgraded (fuel pump & injectors) to support ProCharger system
- McLeod RST twin disk clutch with aluminum flywheel
The problem is that when driving the vehicle say 2500 rpm if you push in the clutch coming up to a stop, the vehicle's RPMs go down to say 1000 RPM briefly and then about 4 seconds later fall to around 500 and then back up to 1000. Once it starts, this will cycle for the entire time the vehicle is moving. When the vehicle finally comes to a complete stop it idles correctly around 600 RPM.
Does anyone have any clues I can give them to help solve this problem??
10-26-2016, 09:10 AM
#2
Team Owner
I've tried a number of solutions on my own car for that problem, though mine isn't boosted. The howto's I've found on the web pretty much suck, though my car is due for a new PCM today that might be the cause of why those don't work on my car. I ended up turning off the throttle cracker altogether and then tweaked the timing down at idle very slightly to get it where my 9* overlap car idles smooth at 800. It takes some time and a few tries to get it right. That was my experience anyway.
How many of these have they done? After a few I should think they'd have the tame idle to a science. But then again I'm new to this so what do I know. It's fairly well documented on the web that this is one of the more complicated aspects of tuning.
How many of these have they done? After a few I should think they'd have the tame idle to a science. But then again I'm new to this so what do I know. It's fairly well documented on the web that this is one of the more complicated aspects of tuning.
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tommypenguin (10-26-2016)
10-26-2016, 11:23 PM
#3
Le Mans Master
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St. Jude Donor '13-'14-'15
With any highly modded engine whether cammed or boosted you will run into dying issues when coming to a stop--
If you still have the stock cam it should be an easy tune fix to correct a coast down off throttle dying or low RPM surging issue
1. Typically with a SC application due to the boost pop off happening when you lift the engine will try to die---This is due to the stock "DFCO" system which shuts off the fuel when you lift off the gas--This table is based on manifold MAP pressure--But because of spikey MAP reading with a pop off the MAP readings go crazy for awhile
To correct this tuners will simply turn OFF the DFCO system (deceleration fuel cut-off)
If this does not correct the dying in gear when lifting the 2nd fix would be to go to your "throttle follower table" in gear on a manual trans---Start by removing 10% to that entire table----Keep subtracting until the dying stops-----If you go too far you will get the opposite affect--a "hanging idle" if that happens simply back off the % somewhat
If you still have the stock cam it should be an easy tune fix to correct a coast down off throttle dying or low RPM surging issue
1. Typically with a SC application due to the boost pop off happening when you lift the engine will try to die---This is due to the stock "DFCO" system which shuts off the fuel when you lift off the gas--This table is based on manifold MAP pressure--But because of spikey MAP reading with a pop off the MAP readings go crazy for awhile
To correct this tuners will simply turn OFF the DFCO system (deceleration fuel cut-off)
If this does not correct the dying in gear when lifting the 2nd fix would be to go to your "throttle follower table" in gear on a manual trans---Start by removing 10% to that entire table----Keep subtracting until the dying stops-----If you go too far you will get the opposite affect--a "hanging idle" if that happens simply back off the % somewhat
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ArmchairArchitect (01-25-2017)
10-28-2016, 07:52 AM
#4
7th Gear
Thread Starter
Thanks for the input, I really appreciate the Corvette Form support.
Here is what the tuner is telling me. Has anyone experienced what they are saying and is it just something I need to accept as part of ProCharging my car?
"What these people are referring to is stalling, or dropping RPM too quickly which can cause the swing to happen. What your car is doing is very different as it stabilizes (or starts to) and then loses control. Truthfully, this is not uncommon on these cars, and there are points where some cars just can never be perfect because the computer is advanced enough to do many things, but not quite advanced enough to do everything asked of it. Typically speaking, this is at levels far higher than yours is at, but it is still a possibility."
Here is what the tuner is telling me. Has anyone experienced what they are saying and is it just something I need to accept as part of ProCharging my car?
"What these people are referring to is stalling, or dropping RPM too quickly which can cause the swing to happen. What your car is doing is very different as it stabilizes (or starts to) and then loses control. Truthfully, this is not uncommon on these cars, and there are points where some cars just can never be perfect because the computer is advanced enough to do many things, but not quite advanced enough to do everything asked of it. Typically speaking, this is at levels far higher than yours is at, but it is still a possibility."
10-28-2016, 08:50 AM
#5
Team Owner
No, I don't buy it. As I say I'm going through something similar on my own car and there is no reason I can't fix it. Mine went from unable to run yesterday (totally starting from scratch on the tune with a new controller) to today, enough torque at idle for me to drive the car as normal and no surging idle. Mine is idling right now at 800rpms smoothly with a cam that's got 9* of overlap. 234/236 ..596/.598. Could just call it .600/.600.
Take this as a statement of someone who's talking out their *** and has 1 day of tuning experience...
A primary key is the timing transition from the main spark table to the idle tables. If they are way off or the idle fueling is way off during that, then the transition will cause a dramatic change in the way the car runs. So, in motion (>1mph) it'll idle but sitting it won't, or vice versa. Or, as you attempt to let the clutch out it'll go from 'ok' torque at 800rpm to 0 torque at 600. That needs tuned out.
I suspect if my log wasn't lost this morning I'll have that fixed later today, though it looks like much later.
Take this as a statement of someone who's talking out their *** and has 1 day of tuning experience...
A primary key is the timing transition from the main spark table to the idle tables. If they are way off or the idle fueling is way off during that, then the transition will cause a dramatic change in the way the car runs. So, in motion (>1mph) it'll idle but sitting it won't, or vice versa. Or, as you attempt to let the clutch out it'll go from 'ok' torque at 800rpm to 0 torque at 600. That needs tuned out.
I suspect if my log wasn't lost this morning I'll have that fixed later today, though it looks like much later.
10-30-2016, 12:04 AM
#6
Le Mans Master
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St. Jude Donor '13-'14-'15
I agree that on a cammed engine you need to add at least 3-4 * to the base idle timing tables to prevent the off idle dying----
It is common after certain mods to have the RPM's dip after lifting---However this should only be a brief one time bounce---If the idle bounces more than once--It needs to be corrected
A C5 is very easy to tune for this issue as is a C6 But the new C7 ECM is much more compicated and can be tricky
I always----
1. add 3-4* of timing to the base timing in P/N and in gear to aid in the transition when lifting
2. With mid to large cams I always delete the DFCO
3. I always start by subtracting 10% to either the throttle follower in gear or the throttle follower in P/N or both depending if there is a dying issue on either senario
4 Very rare usually only if you install a larger t-body than stock--- you can modify the "throttle cracker" as well similarly as the follower to get rid of idle dying
PS taking for granted you already raised the "desired idle speed" up from the low horrible stock 550 RPM to something more reasonable like 625----If you have a cam th idle speed may have to be set even higher !!
And finally this is assuming that your tuner has re calibrated ALL your fuel trims at idle and P/T so they read at least "0" or slightly negative---This should be done 1st before you ever attempt to adjust any other tables to correct dying
It is common after certain mods to have the RPM's dip after lifting---However this should only be a brief one time bounce---If the idle bounces more than once--It needs to be corrected
A C5 is very easy to tune for this issue as is a C6 But the new C7 ECM is much more compicated and can be tricky
I always----
1. add 3-4* of timing to the base timing in P/N and in gear to aid in the transition when lifting
2. With mid to large cams I always delete the DFCO
3. I always start by subtracting 10% to either the throttle follower in gear or the throttle follower in P/N or both depending if there is a dying issue on either senario
4 Very rare usually only if you install a larger t-body than stock--- you can modify the "throttle cracker" as well similarly as the follower to get rid of idle dying
PS taking for granted you already raised the "desired idle speed" up from the low horrible stock 550 RPM to something more reasonable like 625----If you have a cam th idle speed may have to be set even higher !!
And finally this is assuming that your tuner has re calibrated ALL your fuel trims at idle and P/T so they read at least "0" or slightly negative---This should be done 1st before you ever attempt to adjust any other tables to correct dying
10-30-2016, 12:04 PM
#7
7th Gear
Thread Starter
I talked with the tuner more about this problem and relayed the suggestions posted. I'm planning on dropping the vehicle back off to them sometime this week to have the issue corrected. They told me to plan to have the vehicle at there shop for an extended period (week to weeks) to get this resolved and even then cannot guarantee it will be fixed when they return it. I'm not sure I want them to have the vehicle that long as winter is just around the corner and I would like to store the vehicle soon, but it is what it is at this point.
10-30-2016, 03:37 PM
#8
I talked with the tuner more about this problem and relayed the suggestions posted. I'm planning on dropping the vehicle back off to them sometime this week to have the issue corrected. They told me to plan to have the vehicle at there shop for an extended period (week to weeks) to get this resolved and even then cannot guarantee it will be fixed when they return it. I'm not sure I want them to have the vehicle that long as winter is just around the corner and I would like to store the vehicle soon, but it is what it is at this point.
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ArmchairArchitect (01-25-2017)
10-30-2016, 05:51 PM
#9
Team Owner
If it were me I'd be looking for a large timing swing in the logs. If you're getting that, figure out where that's coming from and You've probably found the issue. IF you're seeing fueling issues, that should be easy to correct with a wideband and a scan.
11-08-2016, 01:09 PM
#10
I talked with the tuner more about this problem and relayed the suggestions posted. I'm planning on dropping the vehicle back off to them sometime this week to have the issue corrected. They told me to plan to have the vehicle at there shop for an extended period (week to weeks) to get this resolved and even then cannot guarantee it will be fixed when they return it. I'm not sure I want them to have the vehicle that long as winter is just around the corner and I would like to store the vehicle soon, but it is what it is at this point.
11-13-2016, 06:46 PM
#12
7th Gear
Thread Starter
Performance shop is telling me they can't get to my vehicle to correct the problem until the first week in December. I told them it will have to wait until next spring as I am putting the vette into storage by thanksgiving weekend.
I will update my post when the problem gets corrected.
I'm going to try to attach a video of my problem for others to reference. The video shows the problem at 60 to 70 mph but it occurs any time the vehicle is rolling with no throttle input.
I will update my post when the problem gets corrected.
I'm going to try to attach a video of my problem for others to reference. The video shows the problem at 60 to 70 mph but it occurs any time the vehicle is rolling with no throttle input.
11-14-2016, 01:04 PM
#13
Performance shop is telling me they can't get to my vehicle to correct the problem until the first week in December. I told them it will have to wait until next spring as I am putting the vette into storage by thanksgiving weekend.
I will update my post when the problem gets corrected.
I'm going to try to attach a video of my problem for others to reference. The video shows the problem at 60 to 70 mph but it occurs any time the vehicle is rolling with no throttle input.
I will update my post when the problem gets corrected.
I'm going to try to attach a video of my problem for others to reference. The video shows the problem at 60 to 70 mph but it occurs any time the vehicle is rolling with no throttle input.
I’ve taken some time to review this thread and am sorry to hear your ‘Vette’s RPMs are fluctuating. I know you mentioned you’re putting your car in storage in the next couple weeks, but if we can assist with this concern, please don’t hesitate to send us a private message.
Steph B
Chevrolet Customer Care
11-15-2016, 11:48 AM
#15
My car experienced this after installing a new clutch with lightened flywheel. It's an LS3 with mild cam and the lighter flywheel resulted in the stalling issue. Driving for a few days smoothed this out so it is much better but the tune could use some tweaks.