Really lost on fuel trims
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TECH Apprentice
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Joined: Jul 2005
Posts: 346
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From: Mansfield, TX
Really lost on fuel trims First off I do NOT have a WfB and I am trying to tune my car with the narrow band O2 sensors( no WOT). I for some reason cannot understand why my car smell soooooo rich at idle and part throttle, my fuel trims are reading somewhere +- 2. I dont know what to do, I was thinkig if I lowered my VE table in the idle section it would lean it out but if the FT's are good wouldnt the pcm see that and richen it back up? Maybe I am missing the big picture here or something, I have been reading up on things and all I can really find is YOU HAVE TO HAVE A WB. I think the car is way too rich throughout though, friend tuned it and I bought HP tuners because things didnt seem right, LT fuel trims were +22-25 so the only thing I have done is mess with the ve table and worried I have it hosed Up LOL. Here is a tune file if anyone has a few minutes to take a look. Nevermind it wont let me add an attachment right now, anyone have a clue if the PCM will richen it up if I lean out the idle section of the VE table?
Thread Starter
TECH Apprentice
iTrader: (28)
Joined: Jul 2005
Posts: 346
Likes: 2
From: Mansfield, TX
O2 sensors are ggod, they are fairly new and are nnot slow or flatlining. They do get fairly lazy at idle though, are they supposed to be lazy at idle? Mechanically the car is good, burns some oil that about it, and I am running without cats. i am learning how to tune because I have been burned before on a 350.00 tune that was junk and the guy went out of buisness, then a friend tried and didnt help much. Anyway thanks for the replys guys, it is a tough road learning this stuff!
What does rich smell like to you? Are you sure your
nose knows?
Here's my smell guide, for what it's worth:
Minor rich smells sweet or "dead" - nothing but water,
CO2 and CO.
Balanced has no smell.
Leaner you start to smell sour. That's the NOx making
acid with the water vapor.
Way lean, or way rich, you will start to bump the HC
up. This is your gas smell. Sour + gas, too lean; gas
and not-sour, too rich.
Try disabling closed loop before you do anything else,
or the system will fight you. You can't use the trims
then, but you can use the average or the real-time
NBO2 as an up/down indicator. I used to work this
way before widebands were so available so cheap
(relatively; used to be $600 before Bosch came out
with their cheap sensors). Like if you see <200mV,
add 2%, 200-350mV add 1%, 650-800mV subtract 1%,
>800mV subtract 2%. That will get you lined up in a
few sessions, everywhere you hit with an EQ=1.000.
You can mess around the EQ table and extend the
region of even fueling quite a ways if you pull out
enough spark to avoid KR.
One thing that goes on with closed loop fueling is
fuel dithering (proportional fueling), the PCM tries to
force the sensors to chatter so it gets enough crosses
to keep it happy. But it can swing over-wide especially
at low RPM and that makes a continual "soup" of too-
lean and too-rich byproducts, every kind of stank
all in one so you can't tell what's what, as far as the
center point, because (a) center doesn't smell and
(b) you aren't spending any time there.
nose knows?
Here's my smell guide, for what it's worth:
Minor rich smells sweet or "dead" - nothing but water,
CO2 and CO.
Balanced has no smell.
Leaner you start to smell sour. That's the NOx making
acid with the water vapor.
Way lean, or way rich, you will start to bump the HC
up. This is your gas smell. Sour + gas, too lean; gas
and not-sour, too rich.
Try disabling closed loop before you do anything else,
or the system will fight you. You can't use the trims
then, but you can use the average or the real-time
NBO2 as an up/down indicator. I used to work this
way before widebands were so available so cheap
(relatively; used to be $600 before Bosch came out
with their cheap sensors). Like if you see <200mV,
add 2%, 200-350mV add 1%, 650-800mV subtract 1%,
>800mV subtract 2%. That will get you lined up in a
few sessions, everywhere you hit with an EQ=1.000.
You can mess around the EQ table and extend the
region of even fueling quite a ways if you pull out
enough spark to avoid KR.
One thing that goes on with closed loop fueling is
fuel dithering (proportional fueling), the PCM tries to
force the sensors to chatter so it gets enough crosses
to keep it happy. But it can swing over-wide especially
at low RPM and that makes a continual "soup" of too-
lean and too-rich byproducts, every kind of stank
all in one so you can't tell what's what, as far as the
center point, because (a) center doesn't smell and
(b) you aren't spending any time there.
Thread Starter
TECH Apprentice
iTrader: (28)
Joined: Jul 2005
Posts: 346
Likes: 2
From: Mansfield, TX
Lol Jimmy, I always love reading your post! I will put the sniffer on it tommorow and let you know how it smell, I can tell you stat it will burn your eyes at idle. So just to clarify I shoud watch the NB O2's in the histogram watching their average and adjust from there. I am glad you mentioned that because I have never thought about watching the average. What is the magic number I am looking for 450Mv? Thanks!
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Thread Starter
TECH Apprentice
iTrader: (28)
Joined: Jul 2005
Posts: 346
Likes: 2
From: Mansfield, TX
I am going to post up a 10 minute log I did this morning, would have done more but the laptop battery SUCKS ***. I looked at the Histogram and they NB O2 data and looks like they are ready 650 ish cruising and I wonder why.......Can I even look at those as a "tuning" tool or disregard them and I also may have a wideband tomorrow if the place is open. Thanks for the help, I used the standard config. nothing special
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