What determines the L-Trims?
10-13-2004, 05:37 PM
#1
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What determines the L-Trims? Where do the L-trim readings come from? do they read off of the o2 sensors? The reason I ask is beacuse when I autotap the car my L-trims will read for like 5-10 minutes then they will go to 0 and never move again (Please dont say I wish my L-trims were always at 0). The reason I ask is because i am throwing a code for both front o2's slow response. Thanks.
10-13-2004, 07:49 PM
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When you unplug the sensor the car defaults to open
loop operation. Quite possibly, the O2 codes cause the
same thing (and your trims go away).
The PCM wants to see lots of threshold crossings on
the O2 signal, and equal time above and below the line.
It increments or decrements the LTFT value when it
sees a gross offset. But if it can't see nuthin' on account
of the lights went out, it gives up on that and just makes
the best of things.
Headers put a sleeper hold on the O2s, at low exhaust
flow.
loop operation. Quite possibly, the O2 codes cause the
same thing (and your trims go away).
The PCM wants to see lots of threshold crossings on
the O2 signal, and equal time above and below the line.
It increments or decrements the LTFT value when it
sees a gross offset. But if it can't see nuthin' on account
of the lights went out, it gives up on that and just makes
the best of things.
Headers put a sleeper hold on the O2s, at low exhaust
flow.
10-25-2004, 12:21 AM
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hey what do you mean when you said "the header puts a sleeper hold on the o2 sensors" also is what the following post said true about the car not adding or taking fuel until the number is more than 10 or less than -10. thanks 
10-25-2004, 12:43 AM
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I think he meant that with LT headers, the 02s are located much further downstream. At idle their is a relatively low amount of air going through and so the 02s get "lazy".
10-25-2004, 08:35 AM
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Yes, the LT headers put the sensors like 2-3 feet
further away,and in between put maybe 4-8X the
cooling surface area to shed heat from the exhaust.
When the gas is moving slow it can get below the
minimum working temp of the sensors. Then you see
the O2 voltage, instead of bopping around all happy
and responsive, just crashing out.
"When I die I want to go peacefully, in my sleep, like
my grandfather. Not screaming in terror like his
passengers".
I've seen it said that the STFTs have to exceed 10
for update to happen. Not sure if I believe it, but
no basis to say otherwise. I have seen my LTFTs
update a lot faster than other people have indicated
they should. But I rarely log or look at STFTs, so
haven't made that correlation.
further away,and in between put maybe 4-8X the
cooling surface area to shed heat from the exhaust.
When the gas is moving slow it can get below the
minimum working temp of the sensors. Then you see
the O2 voltage, instead of bopping around all happy
and responsive, just crashing out.
"When I die I want to go peacefully, in my sleep, like
my grandfather. Not screaming in terror like his
passengers".
I've seen it said that the STFTs have to exceed 10
for update to happen. Not sure if I believe it, but
no basis to say otherwise. I have seen my LTFTs
update a lot faster than other people have indicated
they should. But I rarely log or look at STFTs, so
haven't made that correlation.
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10-25-2004, 11:16 AM
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not trying ot hijack this thread but id like ot ask a ? i just installed LT headers and now ever once in a while ill get a code low voltage on the O2's and it is going it on both sides B1 and B2. i never got the codes before the header install chould this be from what you was talking about the O2's being lazey since there downstream futher?
thanks
Eddie
thanks
Eddie
10-25-2004, 06:34 PM
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My car is a 98 just like yours and i started throwing O2 codes right after my long tube install. If you havent changed your 02's got to your local auto parts store and buy the back ones from a 98+ corvette. They are the same things except the wires are longer then you can throw away your wire extensions. It was like the old O2's had so many miles on them and were just used to being in the stock manifolds and they are angry cause they got moved back so far from the longtubes.
10-25-2004, 08:52 PM
#11
The 02 output is supposed to transition above and below 450mVolts at least 3 times per second. When you say 10 I assume you mean 1000mVolts or 1 Volt. The is for the pre-cat 02s. The post cat 02s are supposed to look similar, but with less amplitude if the cats are working properly. Like a sine wave that got smashed a little. When the pre-cat 02 values get out of range either above or below 14.7 A/F the LTFTs move to get the STFTs back into the CENTER of the range.
10-25-2004, 09:04 PM
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Originally Posted by eallanboggs
The 02 output is supposed to transition above and below 450mVolts at least 3 times per second. When you say 10 I assume you mean 1000mVolts or 1 Volt. The is for the pre-cat 02s. The post cat 02s are supposed to look similar, but with less amplitude if the cats are working properly. Like a sine wave that got smashed a little. When the pre-cat 02 values get out of range either above or below 14.7 A/F the LTFTs move to get the STFTs back into the CENTER of the range.
i think the STFTs move to get the LTRIMS back in line, since the STRIMS are close to narrowband output than the LTRIMS. The LTRIMS are just an average of the STRIMS
10-25-2004, 09:28 PM
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yep i got the bosch one they r part # 13111 they r actually to long and i had to zip tie some of the extra wire up. I think they were like $160 for a pair with tax included. around $75 a peice and the stock size were like $67 a piece. Just make sure you check the box before you leave cause i noticed a few stores carry the part # 13111 and it is the exact same as the stock ones when they should be the longer ones. They were either boxed wrong from bosch or someone did switched them to get the cheaper price. If u do a search you will find a few posts about it (keyword oxygen and sensor i think).
10-25-2004, 09:30 PM
#15
Originally Posted by HumpinSS
i think the STFTs move to get the LTRIMS back in line, since the STRIMS are close to narrowband output than the LTRIMS. The LTRIMS are just an average of the STRIMS
10-25-2004, 10:01 PM
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http://www.hptuners.com/forum/YaBB.pl?action=search2
The STRIMS move around and the LTRIMS are the average of the STRIS over a period of time. STRIMS are closest to a narrow band output and with the 1.5 update we will be able to turn of LTRIM learning to tune via the STRIMS. As I understand it STRIMS are faster moving and more accurate of the 14.7:1 AFR the LTRIMS are just an average of all of the STRIMS that move around across STIOCH
Not to argue but to me Short Term and Long term say exaclty what they would do in reference to time. Long being an average and short being realtime...
The STRIMS move around and the LTRIMS are the average of the STRIS over a period of time. STRIMS are closest to a narrow band output and with the 1.5 update we will be able to turn of LTRIM learning to tune via the STRIMS. As I understand it STRIMS are faster moving and more accurate of the 14.7:1 AFR the LTRIMS are just an average of all of the STRIMS that move around across STIOCH
Not to argue but to me Short Term and Long term say exaclty what they would do in reference to time. Long being an average and short being realtime...
10-25-2004, 10:33 PM
#17
Yeah I agree with what you're saying, i just read "get them back in line" as "get them close to zero". Strims move the ltrims, and as a result the strims move toward zero. Like if you had average strims of 15, your ltrim would update to 15, and then your strims would average around 0. I think we're saying the same thing actually.
10-25-2004, 10:43 PM
#18
Aha, I knew I read that 10% thing somewhere. From Corvette Fuel Injection:
"But if the short term fuel trim continues for more than ten seconds at more than +- 10% the computer will decide that the condition is not momentary, and initiates a long term correction"
"LTFT compensates for changes in the engine over time. This includes STFT at more than +- 10% for more than ten seconds.
"But if the short term fuel trim continues for more than ten seconds at more than +- 10% the computer will decide that the condition is not momentary, and initiates a long term correction"
"LTFT compensates for changes in the engine over time. This includes STFT at more than +- 10% for more than ten seconds.
