Fuel Trim Numbers
10-19-2014, 01:16 PM
#1
TECH Apprentice
Thread Starter
Fuel Trim Numbers Hi All,
I recently got a real time diagnostic gauge and hooked it up to my Z. I was reading the long fuel trim numbers for both banks and noticed quite a difference between bank 1 and 2. Bank one was in single digits to negative numbers and bank 2 was almost always in the teens. The o2 voltage was also not uniform between the front banks.
I know nothing about reading FI information like this.
Motor is a 5.7 cam, ls6 intake, LT headers, 3 in exhaust, no cats. The car was tuned by a highly recommended person on this site.
Engine runs good, lots of power, but to me I figure those numbers should be more uniform.
Am I off here or what?
I recently got a real time diagnostic gauge and hooked it up to my Z. I was reading the long fuel trim numbers for both banks and noticed quite a difference between bank 1 and 2. Bank one was in single digits to negative numbers and bank 2 was almost always in the teens. The o2 voltage was also not uniform between the front banks.
I know nothing about reading FI information like this.
Motor is a 5.7 cam, ls6 intake, LT headers, 3 in exhaust, no cats. The car was tuned by a highly recommended person on this site.
Engine runs good, lots of power, but to me I figure those numbers should be more uniform.
Am I off here or what?
10-19-2014, 01:55 PM
#2
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No matter how well it's tuned, long tubes make for trouble
at idle. Differences in sensor position make for differences
in sensor behavior (esp. when cold outside) when the gas
is getting cooled between motor and sensor. Sensor aging
can also proceed nonuniformly (and false trimming leads to
false enrichment leads to soot leads to faster aging leads
to worse false trimming...).
You don't need and shouldn't expect dead even numbers
when the plumbing and fuel delivery are never identical
bank to bank, even from factory. If sensor waveforms are
fast and tight, you're good and the numbers are what they
are. If sensors get slow and bottom out, top out, then the
fuel trimming (in that region of operation) has to be suspect
and AFR is likely whacked.
at idle. Differences in sensor position make for differences
in sensor behavior (esp. when cold outside) when the gas
is getting cooled between motor and sensor. Sensor aging
can also proceed nonuniformly (and false trimming leads to
false enrichment leads to soot leads to faster aging leads
to worse false trimming...).
You don't need and shouldn't expect dead even numbers
when the plumbing and fuel delivery are never identical
bank to bank, even from factory. If sensor waveforms are
fast and tight, you're good and the numbers are what they
are. If sensors get slow and bottom out, top out, then the
fuel trimming (in that region of operation) has to be suspect
and AFR is likely whacked.
10-19-2014, 02:00 PM
#3
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You are correct the numbers for bank 2 shouldn't be in the teens, you want it as close to zero as possible and it can be positive or negative. But as long as it's single digit numbers those are perfectly fine because they will change day to day depending on weather conditions. So bank 1 is probably fine, but bank 2 could have something slightly off like maybe an o2 sensor or it could be in the tune as well. I'd check the o2 sensor first. I'm still learning as well but that's what I know, hope this helps.