Car hesitating and stumbling don't know why???
10-15-2004, 04:42 PM
#1
On The Tree
Thread Starter
iTrader: (2)
Join Date: Oct 2002
Location: Newport News, VA
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Car hesitating and stumbling don't know why??? I recently just got done with my Trex and Prc heads setup and the car ran fine for a couple of days. Then the car started to stumble and hesitate. THis is a list of everything I did so far.
1. Change p0121 to 75 85
2. changed both o2's
3 new plugs and wires
4. checked for vacume leak
5. did a crank relearn
Every gear and specially first gear the starts hesitates then feals like its going to cut out and then accelerates again. please help.
1. Change p0121 to 75 85
2. changed both o2's
3 new plugs and wires
4. checked for vacume leak
5. did a crank relearn
Every gear and specially first gear the starts hesitates then feals like its going to cut out and then accelerates again. please help.
10-15-2004, 04:59 PM
#2
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
I believe this relates to the speed-density tune. On
"unsteady MAP" conditions the MAF is ignored and
the SD tune is all you have for fuel shot calculation.
I suspect, but do not know for sure, that the loop
is also opened during transients like this so trimming
does not fix things.
Heads & cam (and probably prior mods too) have
made gross changes to the pumping characteristics
of the motor but the VE table has not been updated
to track so the SD tune is not doing you right. This
is likely your stumble and if you looked at the O2
voltages you will probably see them crashing low
and then recovering, or pegging high. But once the
MAP stabilizes the MAF tune comes back on line and
the loop closes, you get trued up and take off.
So anyway I think it's tuning time, or maybe half past,
and the tuning needs more than just WOT dyno style
optimization - you're after full-envelope drivability
which wants more time and care.
Looks like you have some means of tuning, so check out
the various SD/VE table threads and see what that angle
does for you. As a guess, you want to bring low-RPM
VE down and mid- to high-RPM up. Check some VE table
examples on the HPTuners 'board, one of them might be
from a similar sort of vehicle; also Horist's repository may
have a .bin you can take info from.
"unsteady MAP" conditions the MAF is ignored and
the SD tune is all you have for fuel shot calculation.
I suspect, but do not know for sure, that the loop
is also opened during transients like this so trimming
does not fix things.
Heads & cam (and probably prior mods too) have
made gross changes to the pumping characteristics
of the motor but the VE table has not been updated
to track so the SD tune is not doing you right. This
is likely your stumble and if you looked at the O2
voltages you will probably see them crashing low
and then recovering, or pegging high. But once the
MAP stabilizes the MAF tune comes back on line and
the loop closes, you get trued up and take off.
So anyway I think it's tuning time, or maybe half past,
and the tuning needs more than just WOT dyno style
optimization - you're after full-envelope drivability
which wants more time and care.
Looks like you have some means of tuning, so check out
the various SD/VE table threads and see what that angle
does for you. As a guess, you want to bring low-RPM
VE down and mid- to high-RPM up. Check some VE table
examples on the HPTuners 'board, one of them might be
from a similar sort of vehicle; also Horist's repository may
have a .bin you can take info from.
10-15-2004, 05:00 PM
#3
On The Tree
Thread Starter
iTrader: (2)
Join Date: Oct 2002
Location: Newport News, VA
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
I just unpluged my map sensor to see how the car would act while it was running. When I unpluged it the car didn't bog as bad as did and had more throttle response. Pluged the map back in and the car hesitates with more throttle. I just took a 300 mi trip logging and no dtc's poped up. Also checked fuel preasure and it is at 61 psi and just drops about 1 psi under load.
10-15-2004, 05:02 PM
#4
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
In some of these VE threads I see people talking about
reversion from big cams messing up the MAF. Maybe a
straight speed-density tune is your ticket. If you are
done changing hardware around for a while, anyway.
reversion from big cams messing up the MAF. Maybe a
straight speed-density tune is your ticket. If you are
done changing hardware around for a while, anyway.
10-15-2004, 10:59 PM
#6
TECH Addict
Join Date: Feb 2004
Posts: 2,826
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by jimmyblue
In some of these VE threads I see people talking about
reversion from big cams messing up the MAF. Maybe a
straight speed-density tune is your ticket. If you are
done changing hardware around for a while, anyway.
reversion from big cams messing up the MAF. Maybe a
straight speed-density tune is your ticket. If you are
done changing hardware around for a while, anyway.
