What long term fuel trim numbers are acceptable with an intake? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

ZiG · 04-03-2015, 12:12 AM

Not getting much that I can understand when I search.. Put a Rotofab on an otherwise stock LS3 and after about 60 miles of granny driving my LTFT value has gone from -.75/-1.0 (each bank) to somewhere around the -6.75/-7.0 range. Is this normal/acceptable?

If it matters, this was checked with the engine off and using the Torque app with a bluetooth OBDII module.

Also, from what I read there seems to be a discrepancy on how different programs report the LTFT in terms of whether a negative number means adding or subtracting fuel. How can I tell? I want to assume it's adding fuel because it's getting more air now, but that's just an intuitive guess..

376LS3 · 04-03-2015, 01:51 AM

On a stock tune I would say anything less than 10% would be acceptable. The computer can go as high as 25% though so it really doesnt matter. On a tuned car, +/- 5% is what I consider acceptable.

2SSCAMARO · 04-03-2015, 06:43 AM

Fuel trims cannot be checked when the engine is off. The engine should be fully warmed up and cruising at a constant speed on level highway. After adding a cold air intake, you would generally expect to see the trims shift somewhat leaner (toward positive numbers). The trims will vary somewhat day to day and season to season. Plus or minus about 4 or 5 percent is generally accepted as being within tolerance.

DJ_BigC · 04-03-2015, 07:36 AM

LTFT's of -10 to +10 is the acceptable range for the stock ECM, when observing fuel trim data you need to make sure the vehicle fuel trim learn status is enabled.

EFI · 04-03-2015, 09:17 AM

Acceptable is what you feel comfortable with, there isn't necessarily a cutoff point.

Both of the previous settings you had (-1 or -7) deliver the same type of fueling (~14.7) to your engine. In the same fashion, having trims of -15 do the same.

Most people are ok with trims in the single digits, especially negative. I personally like to keep my car within 5 both negative and positive, although when I do see a number greater than 3 I tend to adjust the tune for it. But that's being a stickler and having access to a tuner. If I didn't I'd be ok with up to 7 or so.

I keep my trims that low because along with a smooth table, it makes for a very nice responsive driving car. If you have wild swings with jagged transistions then your driveability suffers but the engine still lives perfectly fine, another example of this being a personal opinion and not a set cutoff of good vs. bad.

ZiG · 04-03-2015, 10:48 AM

Okay, thanks. So if I have to measure it at speed, the LTFT must be a table and not just a fixed value? Alright, makes sense I guess. I'll give that a try, thanks.

Pro Stock John · 04-03-2015, 11:43 AM

LFTMs in +/- 10% would not bother me, like folks said the pcm will compensate up to 25%.

LFTTs as I understand it buffer the fuel corrections... Sure you could do some tuning and reduce the correction.

rvadim76 · 05-09-2015, 10:58 PM

How to check on whether the fuel trim learn status is enabled?
Much appreciated!

04-03-2015, 12:12 AM	#1
ZiG Drives: 2011 2SS/RS LS3 Join Date: Jan 2015 Location: Alberta Posts: 173	What long term fuel trim numbers are acceptable with an intake? Not getting much that I can understand when I search.. Put a Rotofab on an otherwise stock LS3 and after about 60 miles of granny driving my LTFT value has gone from -.75/-1.0 (each bank) to somewhere around the -6.75/-7.0 range. Is this normal/acceptable? If it matters, this was checked with the engine off and using the Torque app with a bluetooth OBDII module. Also, from what I read there seems to be a discrepancy on how different programs report the LTFT in terms of whether a negative number means adding or subtracting fuel. How can I tell? I want to assume it's adding fuel because it's getting more air now, but that's just an intuitive guess..

04-03-2015, 01:51 AM	#2
376LS3 Eh, that'll happen Drives: 2010 2SS Join Date: Apr 2012 Location: Mesa, Arizona Posts: 1,841	On a stock tune I would say anything less than 10% would be acceptable. The computer can go as high as 25% though so it really doesnt matter. On a tuned car, +/- 5% is what I consider acceptable. __________________ 2010 Camaro SS LS3 - No Modz

04-03-2015, 06:43 AM	#3
2SSCAMARO Drives: 2010 Camaro Auto Join Date: Mar 2010 Location: Fl Posts: 1,164	Fuel trims cannot be checked when the engine is off. The engine should be fully warmed up and cruising at a constant speed on level highway. After adding a cold air intake, you would generally expect to see the trims shift somewhat leaner (toward positive numbers). The trims will vary somewhat day to day and season to season. Plus or minus about 4 or 5 percent is generally accepted as being within tolerance. __________________ Just livin' life

04-03-2015, 07:36 AM	#4
DJ_BigC Rockin' Steady Drives: 2010 Camaro 2SS Join Date: Apr 2012 Location: Timmins Posts: 216	LTFT's of -10 to +10 is the acceptable range for the stock ECM, when observing fuel trim data you need to make sure the vehicle fuel trim learn status is enabled. __________________ Eric Carrier, proud GM Technician for over 10yrs. 2010 Camaro 2SS Black, L99, SLP headers, GMPP axle back, complete JRE tune, 22" Boss 337's, Nitto Invos 5% tint, Eforce Supercharger w. 3" pulley, ADM FPCM, ID850's, JRE fuel rail mod, Eforce CAI, Moroso catch can, spark plug insulators.

04-03-2015, 11:43 AM	#7
Pro Stock John Writer Drives: 2010 SS / 1967 Camaro Join Date: May 2009 Location: Chicago, IL Posts: 7,216	LFTMs in +/- 10% would not bother me, like folks said the pcm will compensate up to 25%. LFTTs as I understand it buffer the fuel corrections... Sure you could do some tuning and reduce the correction. __________________ PROJECT HEAVY CHEVY Camaro Now: Mods for the Masses Part I \| Part II 13.15@106 1.95 \| 100% Stock 12.37@112 1.85 \| + Kooks Headers/Cats + 20" 555R + CAI + BW TB + UDP + Tune 12.06@113 1.70 \| + CD 3200 + 18" NT05R + RCR Intake + NE OTR + GPI Tune 11.84@115 1.59 \| + 3.91s + Race Star 17x7 Fronts 10.90@125 1.47 \| + GPI VVT Cam + BW Ported Heads + CD 3800

04-03-2015, 09:17 AM	#5
EFI Drives: something faster than you Join Date: Aug 2010 Location: where dem hoes be Posts: 315	Acceptable is what you feel comfortable with, there isn't necessarily a cutoff point. Both of the previous settings you had (-1 or -7) deliver the same type of fueling (~14.7) to your engine. In the same fashion, having trims of -15 do the same. Most people are ok with trims in the single digits, especially negative. I personally like to keep my car within 5 both negative and positive, although when I do see a number greater than 3 I tend to adjust the tune for it. But that's being a stickler and having access to a tuner. If I didn't I'd be ok with up to 7 or so. I keep my trims that low because along with a smooth table, it makes for a very nice responsive driving car. If you have wild swings with jagged transistions then your driveability suffers but the engine still lives perfectly fine, another example of this being a personal opinion and not a set cutoff of good vs. bad.

04-03-2015, 10:48 AM	#6
ZiG Drives: 2011 2SS/RS LS3 Join Date: Jan 2015 Location: Alberta Posts: 173	Okay, thanks. So if I have to measure it at speed, the LTFT must be a table and not just a fixed value? Alright, makes sense I guess. I'll give that a try, thanks.

05-09-2015, 10:58 PM	#8
rvadim76 Drives: SOLD: 2012 Chevy Camaro 2SS Join Date: Jan 2015 Location: Texas Posts: 560 View My Garage	How to check on whether the fuel trim learn status is enabled? Much appreciated!