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Idle LTFT, STFT and MAP question

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5 replies to this topic

#1
v3n0m

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I’m trying to learn a bit more about how to tube my car and I’m a bit confused with what I’m seeing at idle.

At idle, I’m seeing LTFT of around +15% but STFT around -15%. Meaning it’s net zero trim, right? Why would LTFT not adjust back down to 0 if STFT’s are compensating?

Also what manifold pressure is typical for idle? Is checking that measurement a good way to spot check for a vacuum leak? Or is the MAP value a computer value?

#2
v3n0m

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Also how long does it take for the ECU to compute new LTFT values? Is there any way to reset the learned values?

#3
Doug@WGP

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Depends on model year how fast it learns and unlearns. Stock idle vacuum is about -9-10psi

Doug Ross
Owner of Weapons Grade Performance
-Northeast/Pacific Northwest Shops where we ONLY work on GT-Rs
-Owner/Builder of the 1st Ever Home Garage GT-R Drivetrain Removal
Cobb Protuner / EcuTek Tuner
-All Wheel Drive Mustang Dyno in House
doug@weaponsgradeperformance.com
Our Online Store
East Coast Location 226 N. Plains Industrial Rd, Wallingford CT 06492 203-668-4765


#4
colo_evo

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Also how long does it take for the ECU to compute new LTFT values? Is there any way to reset the learned values?


Hard reset will clear ltft

#5
v3n0m

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Depends on model year how fast it learns and unlearns. Stock idle vacuum is about -9-10psi


Thanks for that. What impacts idle vacuum? I’m sitting at around -10.8 psi, with id1000, 3” intake and exhaust.

Would a vacuum leak impact idle MAP?

#6
Doug@WGP

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Thanks for that. What impacts idle vacuum? I’m sitting at around -10.8 psi, with id1000, 3” intake and exhaust.

Would a vacuum leak impact idle MAP?


That’s normal.

Doug Ross
Owner of Weapons Grade Performance
-Northeast/Pacific Northwest Shops where we ONLY work on GT-Rs
-Owner/Builder of the 1st Ever Home Garage GT-R Drivetrain Removal
Cobb Protuner / EcuTek Tuner
-All Wheel Drive Mustang Dyno in House
doug@weaponsgradeperformance.com
Our Online Store
East Coast Location 226 N. Plains Industrial Rd, Wallingford CT 06492 203-668-4765





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