Need some help with hesitation during acceleration
03-08-2007, 12:26 PM
#1
TECH Enthusiast
Thread Starter
iTrader: (14)
Join Date: Apr 2005
Location: NE Ohio
Posts: 591
Likes: 0
Received 0 Likes
on
0 Posts
Need some help with hesitation during acceleration This has been bugging me for a while and since it has gotten nicer out, I thought I'd take a crack at fixing it finally.
Background: Custom tuned (by me) LS1 with supercharger. Normally runs fine, but started to get an intermittent problem.
Problem: In closed loop operation, sometimes, it will hesitate really bad (to the point of almost dying) when I accelerate normally from a stop. Almost feels like it's running out of gas.
I can force it into open loop, and it runs fine. It hasn't done this when I have the scanner connected, being that the problem is intermittant.
Question: Besides ignoring the O2s, are there any major things happening in open loop vs. closed loop that I'm missing?
BTW, for grins I disconnected the MAF to force it to run in SD mode and the problem was still there.
Background: Custom tuned (by me) LS1 with supercharger. Normally runs fine, but started to get an intermittent problem.
Problem: In closed loop operation, sometimes, it will hesitate really bad (to the point of almost dying) when I accelerate normally from a stop. Almost feels like it's running out of gas.
I can force it into open loop, and it runs fine. It hasn't done this when I have the scanner connected, being that the problem is intermittant.
Question: Besides ignoring the O2s, are there any major things happening in open loop vs. closed loop that I'm missing?
BTW, for grins I disconnected the MAF to force it to run in SD mode and the problem was still there.
03-08-2007, 01:29 PM
#2
TECH Addict
iTrader: (10)
Join Date: Jun 2004
Location: Commerce Twp, MI
Posts: 2,918
Likes: 0
Received 0 Likes
on
0 Posts
It's going to be a big guessing game until you capture some data in a log. It could be fuel, spark, mechanical, etc. What's the rest of the setup (A4/M6, bolt-ons, etc.)???
03-08-2007, 01:51 PM
#3
TECH Enthusiast
Thread Starter
iTrader: (14)
Join Date: Apr 2005
Location: NE Ohio
Posts: 591
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by SSpdDmon
It's going to be a big guessing game until you capture some data in a log. It could be fuel, spark, mechanical, etc. What's the rest of the setup (A4/M6, bolt-ons, etc.)???
Right now I'm trying to pinpoint the differences between Open and Closed loop. I can definately make the problem go away by forcing Open loop.
By determining the differences, I can begin the process of elimination. For example, if timing isn't changed between Open/Closed loop, I can eliminate it. VE/air tables, the same.
03-08-2007, 02:05 PM
#4
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,604
Likes: 0
Received 6 Likes
on
6 Posts
You can't eliminate timing as a variable because timing and fueling
go together.
When you are accelerating, at the point of the problem, what is
your MAP? What commanded EQ results from this in open loop,
perhaps fatter than the 1.000 closed loop target and covering
up an excess advance?
If closed loop is your normal intention for this load-point then
reducing spark would be the ticket. If you want acceleration
there and enrichment then you might just want to bring PE
in earlier. Or shift into a better engine RPM.
I'd settle down the KR attack/decay so you can see better
the real ping-hits without the long lazy tail, log the KR, EQ,
MAP, RPM, TPS and Dynamic Cylinder Air and the delivered
advance. This should let you decide which (fuel or spark)
is out of line.
Another thing that might bug closed loop is the proportional
fuel stuff, it swings rich and lean continuously but if it is
let swing too far, it may bury itself into ping-inducing lean
territory and saddle you with KR even though the average
fueling is right. See if KR follows a bottoming NBO2 cycle
in the waveform, if the waveform is lazy and squared off
then consider reducing the prop fuel amount for that airflow
(and neighbors). You want an edgy sawtooth, not a falling
down drunk looking O2 waveform, keeping you tighter to
center. Long tubes mess this up. It may or may not be an
actor here, just something to look at if nothing else looks
like the problem.
go together.
When you are accelerating, at the point of the problem, what is
your MAP? What commanded EQ results from this in open loop,
perhaps fatter than the 1.000 closed loop target and covering
up an excess advance?
If closed loop is your normal intention for this load-point then
reducing spark would be the ticket. If you want acceleration
there and enrichment then you might just want to bring PE
in earlier. Or shift into a better engine RPM.
I'd settle down the KR attack/decay so you can see better
the real ping-hits without the long lazy tail, log the KR, EQ,
MAP, RPM, TPS and Dynamic Cylinder Air and the delivered
advance. This should let you decide which (fuel or spark)
is out of line.
Another thing that might bug closed loop is the proportional
fuel stuff, it swings rich and lean continuously but if it is
let swing too far, it may bury itself into ping-inducing lean
territory and saddle you with KR even though the average
fueling is right. See if KR follows a bottoming NBO2 cycle
in the waveform, if the waveform is lazy and squared off
then consider reducing the prop fuel amount for that airflow
(and neighbors). You want an edgy sawtooth, not a falling
down drunk looking O2 waveform, keeping you tighter to
center. Long tubes mess this up. It may or may not be an
actor here, just something to look at if nothing else looks
like the problem.
03-08-2007, 08:21 PM
#5
Originally Posted by jimmyblue
........
Another thing that might bug closed loop is the proportional
fuel stuff, it swings rich and lean continuously but if it is
let swing too far, it may bury itself into ping-inducing lean
territory and saddle you with KR even though the average
fueling is right. See if KR follows a bottoming NBO2 cycle
in the waveform, if the waveform is lazy and squared off
then consider reducing the prop fuel amount for that airflow
(and neighbors). You want an edgy sawtooth, not a falling
down drunk looking O2 waveform, keeping you tighter to
center. Long tubes mess this up. It may or may not be an
actor here, just something to look at if nothing else looks
like the problem.
Another thing that might bug closed loop is the proportional
fuel stuff, it swings rich and lean continuously but if it is
let swing too far, it may bury itself into ping-inducing lean
territory and saddle you with KR even though the average
fueling is right. See if KR follows a bottoming NBO2 cycle
in the waveform, if the waveform is lazy and squared off
then consider reducing the prop fuel amount for that airflow
(and neighbors). You want an edgy sawtooth, not a falling
down drunk looking O2 waveform, keeping you tighter to
center. Long tubes mess this up. It may or may not be an
actor here, just something to look at if nothing else looks
like the problem.
The proportional fueling reduction... does it help the issue with some of the really bad long tubes? The stainless seem to do it worse; I'm figure the heat loss plays a large factor.
08-21-2012, 07:51 PM
#6
Teching In
Join Date: Feb 2012
Location: Eastern Shore
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
I am having an issue with hesitation between shifts under all out conditions. It seems to mostly happen going into 3rd gear. I have an ECS installed 1500 novi with their big blower cam. Any suggestions? It is less than 1 week since install.
08-21-2012, 10:08 PM
#7
TECH Enthusiast
Thread Starter
iTrader: (14)
Join Date: Apr 2005
Location: NE Ohio
Posts: 591
Likes: 0
Received 0 Likes
on
0 Posts
To update folks that were subscribed to this thread, I found that my hesitation issue to be caused by intermittent O2 sensors. The O2s (can't recall if it was one or both) were providing bad input to the PCM, which reacted by adding/removing fuel, which resulted in stumbling..
Trending Topics
accelerating, acceleration, bad, big, cam, efi, hesitation, intermittant, lean, ls1, ls7, slight, smell, stuff, tuning
