BLM Tuning - Deceleration on a manual car
06-05-2007, 04:05 PM
#1
Safety Car
Thread Starter
Member Since: Sep 2003
Location: Orange County NY
Posts: 3,571
Received 0 Likes
on
0 Posts
St. Jude Donor '10-'11-'12-'13
BLM Tuning - Deceleration on a manual car
I'm in the process of fuel tuning my '87 manual vette (383, MAF, $6E).
In most of the BLM cells where there is throttle activity and vehicle speed(light load, medium load, low rpms, medium rpms, etc), the BLMs are ranging from 124 to 118, indicating it is a little rich.
In the BLM cells where there is no throttle activity (but there is vehicle speed), mainly deceleration, the BLMs are averaging much higher. They are in the 138 - 144 range.
Is this common for a manual car? To get the "deceleration" BLMs in line, I should concentrate on the DFCO and DF enlean elements, correct?
I am also getting some "popping" out of the exhaust when decelerating. What causes this? Do I tune it out through timing or decel fueling?
Thank you!!
In most of the BLM cells where there is throttle activity and vehicle speed(light load, medium load, low rpms, medium rpms, etc), the BLMs are ranging from 124 to 118, indicating it is a little rich.
In the BLM cells where there is no throttle activity (but there is vehicle speed), mainly deceleration, the BLMs are averaging much higher. They are in the 138 - 144 range.
Is this common for a manual car? To get the "deceleration" BLMs in line, I should concentrate on the DFCO and DF enlean elements, correct?
I am also getting some "popping" out of the exhaust when decelerating. What causes this? Do I tune it out through timing or decel fueling?
Thank you!!
06-05-2007, 04:36 PM
#2
Melting Slicks
I wonder if you have some vacuum leaks that don't rear their heads until decel (high vacuum). This could introduce some extra air that could push your blms to the lean side.
I've never paid much attention to the blms during decel, but it seems that when my MAF is on the money all cells are pretty consistent on or off throttle.
Decel will most likely be under 22 gm/sec. so that puts you into MAF table number #1 and cells 7 and below. You may need to play around with the MAF cal to get a good compromise for cells 7 and below.
Usually if cells 7 and 11 look good at cruise the lower cells fall into line for me.
All my exhaust popping went away when I installed a Comp 503 cam, so I've never spent anytime with decel/pop/dfco tuning since then.
I've never paid much attention to the blms during decel, but it seems that when my MAF is on the money all cells are pretty consistent on or off throttle.
Decel will most likely be under 22 gm/sec. so that puts you into MAF table number #1 and cells 7 and below. You may need to play around with the MAF cal to get a good compromise for cells 7 and below.
Usually if cells 7 and 11 look good at cruise the lower cells fall into line for me.
All my exhaust popping went away when I installed a Comp 503 cam, so I've never spent anytime with decel/pop/dfco tuning since then.
06-05-2007, 05:10 PM
#3
Safety Car
Thread Starter
Member Since: Sep 2003
Location: Orange County NY
Posts: 3,571
Received 0 Likes
on
0 Posts
St. Jude Donor '10-'11-'12-'13
BLM cells 7, 10, and 11 are where most of the acceleration / cruising data is coming from. I'll get those squared away first, then go from there.Thank you!!
06-05-2007, 05:25 PM
#4
Melting Slicks
Posted this over att thirdgen some time ago..
I experience this last summer when tuning some C4ors as well as my own car. I tried to tune it out using "open loop" only and a WB aswell as "closed loop" and using the BLMs as guide, just to experiment.
I still got the same kind of drivability.
I also noticed a major dropp in injector DC during de-accel (0 tps and while not in DFCO ). And this make me suspect that something is triggerd during this contidions, and that the ECM makes some kind of adjustments that we dont se in datamaster/tunerpro.
I got rid of most of my "popping" by add timing.
Cheers
I experience this last summer when tuning some C4ors as well as my own car. I tried to tune it out using "open loop" only and a WB aswell as "closed loop" and using the BLMs as guide, just to experiment.
I still got the same kind of drivability.
I also noticed a major dropp in injector DC during de-accel (0 tps and while not in DFCO ). And this make me suspect that something is triggerd during this contidions, and that the ECM makes some kind of adjustments that we dont se in datamaster/tunerpro.
I got rid of most of my "popping" by add timing.
Cheers
Last edited by devilfish; 06-05-2007 at 05:30 PM.
06-05-2007, 06:44 PM
#5
Advanced
Member Since: Oct 2003
Location: Cave Creek AZ
Posts: 77
Likes: 0
Received 0 Likes
on
0 Posts
devilfish posted...
I got rid of most of my "popping" by add timing.
Hello....Sweden!
Was the popping only during decel or was it at low throttle (<10%). In other words was it only at high vacuum? What do you think is happening by adding more timing at popping conditions? Is the popping due to a lean or rich condition?
After the 396 install I had much less vacuum (idle at 60 kPa) so the dfco MAP conditions had to be changed in the "constants" section. I think I changed it to 35-40 KPa. Stock was around 20-28 kPA. This eliminated the popping at decel.
Beth
I got rid of most of my "popping" by add timing.
Hello....Sweden!
Was the popping only during decel or was it at low throttle (<10%). In other words was it only at high vacuum? What do you think is happening by adding more timing at popping conditions? Is the popping due to a lean or rich condition?
After the 396 install I had much less vacuum (idle at 60 kPa) so the dfco MAP conditions had to be changed in the "constants" section. I think I changed it to 35-40 KPa. Stock was around 20-28 kPA. This eliminated the popping at decel.
Beth
06-05-2007, 08:41 PM
#6
Safety Car
Thread Starter
Member Since: Sep 2003
Location: Orange County NY
Posts: 3,571
Received 0 Likes
on
0 Posts
St. Jude Donor '10-'11-'12-'13
Posted this over att thirdgen some time ago..
I experience this last summer when tuning some C4ors as well as my own car. I tried to tune it out using "open loop" only and a WB aswell as "closed loop" and using the BLMs as guide, just to experiment.
I still got the same kind of drivability.
I also noticed a major dropp in injector DC during de-accel (0 tps and while not in DFCO ). And this make me suspect that something is triggerd during this contidions, and that the ECM makes some kind of adjustments that we dont se in datamaster/tunerpro.
I got rid of most of my "popping" by add timing.
Cheers
I experience this last summer when tuning some C4ors as well as my own car. I tried to tune it out using "open loop" only and a WB aswell as "closed loop" and using the BLMs as guide, just to experiment.
I still got the same kind of drivability.
I also noticed a major dropp in injector DC during de-accel (0 tps and while not in DFCO ). And this make me suspect that something is triggerd during this contidions, and that the ECM makes some kind of adjustments that we dont se in datamaster/tunerpro.
I got rid of most of my "popping" by add timing.
Cheers
I searched Third Gen, but missed that thread - thanks for the link
I'm seeing the same thing - the injector PW (in mSec) goes to 0 for most of it (fuel is cut off completely), but at some point I get really low injector PW figures of about .58 - .81. This might be when the popping occurs. My total timing during this condition is generally 39*. How much timing did you add to clear it up?
Beth - in my case, the popping is only happening during decel. O2 sensor volts are super low (4.44 mv) and my LM1 wideband usually gives me no A/F reading (as if it is on, but the engine isn't running).
06-06-2007, 07:39 AM
#7
Melting Slicks
devilfish posted...
I got rid of most of my "popping" by add timing.
Hello....Sweden!
Was the popping only during decel or was it at low throttle (<10%). In other words was it only at high vacuum? What do you think is happening by adding more timing at popping conditions? Is the popping due to a lean or rich condition?
After the 396 install I had much less vacuum (idle at 60 kPa) so the dfco MAP conditions had to be changed in the "constants" section. I think I changed it to 35-40 KPa. Stock was around 20-28 kPA. This eliminated the popping at decel.
Beth
I got rid of most of my "popping" by add timing.
Hello....Sweden!
Was the popping only during decel or was it at low throttle (<10%). In other words was it only at high vacuum? What do you think is happening by adding more timing at popping conditions? Is the popping due to a lean or rich condition?
After the 396 install I had much less vacuum (idle at 60 kPa) so the dfco MAP conditions had to be changed in the "constants" section. I think I changed it to 35-40 KPa. Stock was around 20-28 kPA. This eliminated the popping at decel.
Beth
popping during decel. I also got some jerking at low rpm and low map ( like in stop and go traffic ). I cured both of theses probleme with more timing.
I use as much as 39 in closed TPS spark advance over 1200rpm. And also I run as much as 42 in low rpm 40-60 kpa area. These helped to cure my problemes.
Cheers
06-06-2007, 07:40 AM
#8
Melting Slicks
Thanks for sharing and for responding on Third Gen, too.
I searched Third Gen, but missed that thread - thanks for the link
I'm seeing the same thing - the injector PW (in mSec) goes to 0 for most of it (fuel is cut off completely), but at some point I get really low injector PW figures of about .58 - .81. This might be when the popping occurs. My total timing during this condition is generally 39*. How much timing did you add to clear it up?
Beth - in my case, the popping is only happening during decel. O2 sensor volts are super low (4.44 mv) and my LM1 wideband usually gives me no A/F reading (as if it is on, but the engine isn't running).
I searched Third Gen, but missed that thread - thanks for the link
I'm seeing the same thing - the injector PW (in mSec) goes to 0 for most of it (fuel is cut off completely), but at some point I get really low injector PW figures of about .58 - .81. This might be when the popping occurs. My total timing during this condition is generally 39*. How much timing did you add to clear it up?
Beth - in my case, the popping is only happening during decel. O2 sensor volts are super low (4.44 mv) and my LM1 wideband usually gives me no A/F reading (as if it is on, but the engine isn't running).
one thing to take noticed of is that during 0 tps you dont use the main spark tabel. You use the closed TPS spark tabel, no matter of the rpm.
So I use 39 degrees of timing on my closed tps tabel, from 1200rpm and up.
Cheers
