InlineSix

What is the normal reading for long term fuel trim?

530i lci has fuel trim figure of -10...-18 so its burning lean. This would normally be a problem but i as engine is lean burn is this still normal? btw, you can see your long term fuel trim ltft figure from obd2 port.

pcy

those numbers are with engine warmed up to operating temp?

JJw

no it means your car is burning rich consistently, the car is cutting back fuel going into the cylinders.

l1tech

Negaive fuel trim numbers mean that the engine is running rich and the computer is cutting back fuel. The numbers will change at different operating conditions such as idle or steady cruise and depending on what the readings are and under what circumstances can be quite handy in troubleshooting. Ideally we want long term fuel trim numbers to be 0 with short term readings bouncing back and forth between -2 and +2 but like I said ideally. Realistically long term numbers that are in the -5 to +5 range are good. Anything outside of that range and I start looking for the cause before it becomes a problem even though the engine is still running well.

InlineSix

[QUOTE=l1tech;1478273Anything outside of that range and I start looking for the cause before it becomes a problem even though the engine is still running well.[/QUOTE]

Is this still true for modern (lean burn) engines?

InlineSix

will check that

l1tech

Lean burn or rich burn engines have nothing to do with the fuel trim numbers.