HP Tuners - Lean stumble when you snap throttle or even try to take off? Any ideas?
09-27-2008, 03:28 PM
#1
Teching In
Thread Starter
Join Date: Jun 2008
Posts: 48
Likes: 0
Received 0 Likes
on
0 Posts
HP Tuners - Lean stumble when you snap throttle or even try to take off? Any ideas? I have been pulling my hair out trying to figure out why I get a lean stumble whenever I snap the throttle, my air fuel goes from 14.6 to 19 for a second and then runs fine. It also doesnt really matter what rpm i'm at - off idle or at 2k still does the same thing...... any thoughts would be awsome!!! I attached the tune currently in the car, and did change the cyl volume hoping it would help but with no good results.
1999 Camaro LQ9 6.0L, 8.5:1 diamond pistons, compstar rods,manley valves, custom bullet racing cam, cometic gaskets, arp studs, 78mm precision turbo, 65lb injectors, running maf for now just got my 2bar map but not installed yet, 6 spd, NXL nitrous 125 shot, 12 psi with methenol..... did i miss anything?
I'll try to post a few datalogs in the next day or two, thanks for the help!
1999 Camaro LQ9 6.0L, 8.5:1 diamond pistons, compstar rods,manley valves, custom bullet racing cam, cometic gaskets, arp studs, 78mm precision turbo, 65lb injectors, running maf for now just got my 2bar map but not installed yet, 6 spd, NXL nitrous 125 shot, 12 psi with methenol..... did i miss anything?
I'll try to post a few datalogs in the next day or two, thanks for the help!
09-27-2008, 04:44 PM
#2
I am new at this but try going over to the hptuners forums and search "transient fuel" it looks like "Let's discuss Transient Fuel" is a good read. Also if you are not running cats I would recommend you turn off CAT over temp protection, its under fuel control> cot,lean cruise. Here is something from the hptuners help file:
Originally Posted by HPTuners Help File
Transient Fuel
The Transient Fuel Tab contains parameters related to Transient Fueling. Due to the port injection configuration of the LS1 engine, a model of fuel transfer from the injector to the cylinder is required. Fuel is not injected directly into the cylinder, but into the airstream aimed at the back of the inlet valve (and port walls) where it subsequently puddles and then boils off (evaporates) into the incoming airstream at a certain rate. The amount of fuel pudding and boiling must be accounted for to ensure optimum fuel delivery. This is particularly true during throttle transients.
During positive throttle (MAP) transients additional fuel must be injected than commanded to account for the fact that not all the fuel injected will make it into the cylinder. If additional fuel were not injected a lean condition would result as more fuel is puddling on the valve and port walls rather than entering the cylinder.
Conversely, during negative throttle (MAP) transients, less fuel needs to be injected than commanded to account for remaining fuel that is still boiling off the walls. If less fuel was not injected a rich condition would result.
Transient Fuel Qualification
Min Fuel Milligrams: Minimum injector pulsewidth used to limit transient adjust fuel.
Transient Fuel Min RPM: Disable Transient Fuel below this RPM.
Transient Fuel Max TPS: Disable Transient Fuel below this TPS if RPM is less than Transient Fuel Min RPM.
Warmup Transient Fuel Correction
Warmup Transient Correction (also known as Stomp Compensation) is used to add additional fuel to transients during engine startup conditions. This is to adjust for conditions of inlet port and valve components not being up to satisfactory temperature. ie. extra fuel puddles on a cold intake.
DFCO TPS Min: Warmup Transient Correction will not be added if TPS below this and exiting DFCO.
Fuel Delta Min Increase: Minimum commanded fuel delta to add correction (only compensate for reasonable sized transients).
Fuel Delta Limit: Negative transient fuel delta threshold to disable correction.
Initial Time Decay Mult vs. ECT: Initial value for time decay multiplier factor.
Time Decay Mult vs. ECT: Initial Time Decay Mult is multiplied by this reduction factor as the decay progresses. Smaller numbers mean faster decay.
Previous Correction Reduction vs. ECT: The previous correction value is reduced by this amount and added to the current correction calculations.
Transient Fuel Film Mass Transfer Calculation
Fuel Boiling Time vs. ECT vs. MAP: Boiling Time value
Fuel On Wall Exp Decay Mult vs. Airflow:
Fuel From Wall Stabilization:
Fuel On Wall Remainder:
Transient Fuel Compensator Gain Calculation
Fuel To Wall Impact Factor vs. Cool Temp vs. MAP:
Impact Factor gain vs. Airflow:
Originally Posted by HPTuners Help File
Transient Fuel
The Transient Fuel Tab contains parameters related to Transient Fueling. Due to the port injection configuration of the LS1 engine, a model of fuel transfer from the injector to the cylinder is required. Fuel is not injected directly into the cylinder, but into the airstream aimed at the back of the inlet valve (and port walls) where it subsequently puddles and then boils off (evaporates) into the incoming airstream at a certain rate. The amount of fuel pudding and boiling must be accounted for to ensure optimum fuel delivery. This is particularly true during throttle transients.
During positive throttle (MAP) transients additional fuel must be injected than commanded to account for the fact that not all the fuel injected will make it into the cylinder. If additional fuel were not injected a lean condition would result as more fuel is puddling on the valve and port walls rather than entering the cylinder.
Conversely, during negative throttle (MAP) transients, less fuel needs to be injected than commanded to account for remaining fuel that is still boiling off the walls. If less fuel was not injected a rich condition would result.
Transient Fuel Qualification
Min Fuel Milligrams: Minimum injector pulsewidth used to limit transient adjust fuel.
Transient Fuel Min RPM: Disable Transient Fuel below this RPM.
Transient Fuel Max TPS: Disable Transient Fuel below this TPS if RPM is less than Transient Fuel Min RPM.
Warmup Transient Fuel Correction
Warmup Transient Correction (also known as Stomp Compensation) is used to add additional fuel to transients during engine startup conditions. This is to adjust for conditions of inlet port and valve components not being up to satisfactory temperature. ie. extra fuel puddles on a cold intake.
DFCO TPS Min: Warmup Transient Correction will not be added if TPS below this and exiting DFCO.
Fuel Delta Min Increase: Minimum commanded fuel delta to add correction (only compensate for reasonable sized transients).
Fuel Delta Limit: Negative transient fuel delta threshold to disable correction.
Initial Time Decay Mult vs. ECT: Initial value for time decay multiplier factor.
Time Decay Mult vs. ECT: Initial Time Decay Mult is multiplied by this reduction factor as the decay progresses. Smaller numbers mean faster decay.
Previous Correction Reduction vs. ECT: The previous correction value is reduced by this amount and added to the current correction calculations.
Transient Fuel Film Mass Transfer Calculation
Fuel Boiling Time vs. ECT vs. MAP: Boiling Time value
Fuel On Wall Exp Decay Mult vs. Airflow:
Fuel From Wall Stabilization:
Fuel On Wall Remainder:
Transient Fuel Compensator Gain Calculation
Fuel To Wall Impact Factor vs. Cool Temp vs. MAP:
Impact Factor gain vs. Airflow:
Last edited by Nitroused383; 09-27-2008 at 04:52 PM.
09-28-2008, 10:19 AM
#4
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
If you have substantial fuel trimming going on, to
make the stoich-point, every time you pop between
trim cells the STFTs restart at zero and shortly
learn back to balance. Meanwhile you are off
mixture-point. If it's all happening in closed loop
look at this aspect, right about the tip-in event.
If it's a lean hole preceding rolling into PE, you
may still have that issue but maybe compounded
with some holdoff of PE mode (TPS, RPM, MAP
thresholds & mode delay, the setup varies with
platform & year, truck tunes are set up for towing
and want changed for hot rods etc.).
make the stoich-point, every time you pop between
trim cells the STFTs restart at zero and shortly
learn back to balance. Meanwhile you are off
mixture-point. If it's all happening in closed loop
look at this aspect, right about the tip-in event.
If it's a lean hole preceding rolling into PE, you
may still have that issue but maybe compounded
with some holdoff of PE mode (TPS, RPM, MAP
thresholds & mode delay, the setup varies with
platform & year, truck tunes are set up for towing
and want changed for hot rods etc.).
10-09-2008, 04:40 PM
#5
Teching In
Thread Starter
Join Date: Jun 2008
Posts: 48
Likes: 0
Received 0 Likes
on
0 Posts
Just replaced the head gaskets and I did have 4 cyl. leaking.... come to find out when you get your heads decked you need to make sure the machine shop has the correct stone to make a really smooth finish for cometics to seal! So I now have the gm 5mil 6.2l gaskets and problem solved..... but i still have the stinking lean stumble! It seems worse when i am holding a steady speed say 55 let off the throttle completly then get back into it, also bogs if i am low throttle shifting below 2500 rpm. here is the latest tune if anybody has some suggestions please feel free to let me know! Thanks for looking!
Trending Topics
10-11-2008, 01:38 AM
#10
I cannot view your tune right now because I forgot my laptop charger. Did you apply your 2Bar SD Map? Try this http://www.hptuners.com/help/ and go to the Getting Started>Demos>Applying a 2 Bar SD Enhancement. I think you need to tune the basics first start off by calibrating your injectors like other have said. I have no idea how to do it but a quick search at the hptuners website should help out. You should be in open loop if you are doing any tuning. Also at the www.hptuners.com/help check out Working with VCM Editor>Tuning How To Section>User Submitted>Speed Density. This is a really good article to help you tune your VE table and to force open loop.
10-16-2008, 04:14 PM
#12
Teching In
Thread Starter
Join Date: Jun 2008
Posts: 48
Likes: 0
Received 0 Likes
on
0 Posts
Finally fixed the problem!!! Running constant open loop, shut off dfco, car runs better than ever and as soon as boost starts to build the a/f goes right down to low 11's like it should! Thanks for the input and ideas!!!
10-18-2008, 09:41 PM
#15
Why would it cause bad gas mileage? Only if you command it to run less than 14.7:1 afr. You may have bad emissions but bad emissions and gas mileage are two different things. While running closed loop the computer is constantly adding and subtracting fuel to switch the o2 sensors back and forth for emissions. If you tune OL you can cruise around around 15.5:1 afr at low map readings to increase your mileage. You can also make your car idle a lot leaner to save on fuel.
