HELP! Lean at Idle and Throttle let off...
HELP! Lean at Idle and Throttle let off... Ok so I'm tuning out a buddy's car that just did Heads/Cam/Headers. I'm tuning in SD, Open Loop Mode and targeting a 13.0 AFR to get the VE table inline. The whole table is perfect with the exception of this forming "ridge" as shown below:
That ridge forming is me trying to compensate for lean wideband readings in those areas. Right now it's not totally formed but the more and more I tune it it gets steeper and steeper and the more fuel I pump in those areas the worse off throttle and idle conditions get... (Probably because of the extreme transitions between fuel cells right?) When cruising at any speed, once throttle is let off the RPMs dive straight down to 500 and sit... Car still runs, just idle speed is terrible... All idle tables are stock except Base Running Airflow which is set a 9.00 for all full operating temps. Playing with timing (adding or removing) makes things only worse, I have it at a spot it likes right now... When I lower that ridge down to flow with the rest of the table, idle and throttle let off behave much nicer but I get super lean readings around that area... What gives???
The only thing I can think of is maybe it's an exhaust leak that's screwing up the wideband info... Anyone know if this is possible??? It doesn't make sense that the table would be just fine and within one cell away just pull lean as crap... I know for a fact that the band clamps on the header collectors are not completely sealed and are leaking somewhat... the wideband sensor is being placed about a foot or so after the collector. No cats... Thanks...
That ridge forming is me trying to compensate for lean wideband readings in those areas. Right now it's not totally formed but the more and more I tune it it gets steeper and steeper and the more fuel I pump in those areas the worse off throttle and idle conditions get... (Probably because of the extreme transitions between fuel cells right?) When cruising at any speed, once throttle is let off the RPMs dive straight down to 500 and sit... Car still runs, just idle speed is terrible... All idle tables are stock except Base Running Airflow which is set a 9.00 for all full operating temps. Playing with timing (adding or removing) makes things only worse, I have it at a spot it likes right now... When I lower that ridge down to flow with the rest of the table, idle and throttle let off behave much nicer but I get super lean readings around that area... What gives???
The only thing I can think of is maybe it's an exhaust leak that's screwing up the wideband info... Anyone know if this is possible??? It doesn't make sense that the table would be just fine and within one cell away just pull lean as crap... I know for a fact that the band clamps on the header collectors are not completely sealed and are leaking somewhat... the wideband sensor is being placed about a foot or so after the collector. No cats... Thanks...
TECH Fanatic
Joined: Mar 2003
Posts: 1,839
Likes: 0
From: La Porte, TX
Hey man that looks like a combination of the DFCO, and Idle fuel proportional tables. Try disabling both and see what that gets ya. Also, have you restructured the VE boundries yet? I assume you raised idle, you might want to try and map out new boundries for the VE.
Originally Posted by WS6snake-eater
Hey man that looks like a combination of the DFCO, and Idle fuel proportional tables. Try disabling both and see what that gets ya. Also, have you restructured the VE boundries yet? I assume you raised idle, you might want to try and map out new boundries for the VE.
Well it's being tuned in open loop so i don't think the idle proportional tables are even being entered right now... as far as the DFCO, it's on stock settings... that wouldn't explain why idle is still so lean though would it??? I know that on my setup the DFCO is still enabled and I have minor lean problems in those areas but nothing like this... My car is running perfect now BTW! I did raise the idle up to 900 though, what does setting boundaries for the VE do??? Thanks Matt...
TECH Fanatic
Joined: Mar 2003
Posts: 1,839
Likes: 0
From: La Porte, TX
Originally Posted by txhorns281
Well it's being tuned in open loop so i don't think the idle proportional tables are even being entered right now... as far as the DFCO, it's on stock settings... that wouldn't explain why idle is still so lean though would it??? I know that on my setup the DFCO is still enabled and I have minor lean problems in those areas but nothing like this... My car is running perfect now BTW! I did raise the idle up to 900 though, what does setting boundaries for the VE do??? Thanks Matt...
BTW DFCO is more aggressive on some cars than on others, you might just want to try and disable it, for the sake of testing out the theory.
Teching In
Joined: May 2002
Posts: 16
Likes: 0
From: Stuttgart, Germany
txhorns281,
Did you get this situation figured out? I'm going through, what looks like, the exact same thing. I'm tuning in SD mode with a wideband and I'm getting this ridge (or valley) that froms right in the middle of the histogram. Also the car goes lean in the upper left portion of the histogram. Would be nice if I could fix it.
Thanks
Did you get this situation figured out? I'm going through, what looks like, the exact same thing. I'm tuning in SD mode with a wideband and I'm getting this ridge (or valley) that froms right in the middle of the histogram. Also the car goes lean in the upper left portion of the histogram. Would be nice if I could fix it.
Thanks
Teching In
Joined: May 2002
Posts: 16
Likes: 0
From: Stuttgart, Germany
Sure am, TSP 231/237 with PP 5.3 heads. Maybe this is something I'll learn to live with.
Does the PCM use Fuel Trim Cells in Open Loop? I'm curious if the placement of my FTC boundaries could cause this. I'm really stretching now...
Does the PCM use Fuel Trim Cells in Open Loop? I'm curious if the placement of my FTC boundaries could cause this. I'm really stretching now...
Trending Topics
Originally Posted by AFPewter
Sure am, TSP 231/237 with PP 5.3 heads. Maybe this is something I'll learn to live with.
Does the PCM use Fuel Trim Cells in Open Loop? I'm curious if the placement of my FTC boundaries could cause this. I'm really stretching now...
Does the PCM use Fuel Trim Cells in Open Loop? I'm curious if the placement of my FTC boundaries could cause this. I'm really stretching now...
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