formula for LTFT's

[rletzgus]

How does the predator calculate LTFT's? I don't have the AFR on my predator. I would like to have some math stuff to fool arouind with. anybody know the formulas? or do you know the size of fuel injectors for 4.8 LS1 engine 2001? does the LTFT's calculate by pulse widthxMAFxbore, stroke etc. Anyone? Thanks.

[06MonteSS]

There are a lot of different tables/sensors used to calculate that info... not sure exactly what they all are, but here's some info I found online...

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Your vehicle's computer has an internal table of values that are used to determine how much fuel should be injected based on other sensor readings. One of the most important sensors used to determine fueling is the Mass Air Flow sensor. This sensor tells the computer how much air is entering the engine. The computer looks at this value along with other sensor values such as air temperature, engine RPMs, etc and calculates the estimated fuel required (via lookup table).

Now this is where the fuel trims come into play. Your vehicle has oxygen sensors in the exhaust which roughly determine the air/fuel ratio. The O2 sensors provide feedback to the vehicle's computer and let the computer know how good of a job it is doing at maintaining a proper air/fuel ratio. If the fueling information pulled from it's internal table is resulting in a rich air/fuel ratio (too much gas), it will update the fuel trims to reduce the amount of fuel requested by the computer.

The actual amount of fuel injected is equal to the amount recommended in the computer's internal table adjusted by the short and long term fuel trims.

The long term fuel trim value is based on the average deviation from ideal air/fuel ratio over a longer time. The short term fuel trim is based on a much shorter time.

[01Z]

or do you know the size of fuel injectors for 4.8 LS1 engine 2001?

The LS1 has a displacement of 5.7 liters and the factory injectors for 2001 is 26 pounds per hour.

I truly don't mean any offense here but if you are mistaken about the designation or displacement of your engine, formulating fuel trims from a complex array of analog data from many sources will be a stretch. It would take a book of information, not a thread of messages to explain all the factors, variables and data to answer your question. Forgive me if I am underestimating your abilities.

This really is rocket science.

[jsk06c6]

The predator doesn't calculate LTFT's, it reads the data from the vehicles computer.

You say your predator doesn't have AFR, is that what you want to calculate, AFR?

[rletzgus]

Yeah. basically trying to see what the AFR is at any given time? And trying to understand what LTFT data is used to calculate. My predator is working great, I noticed a positive difference in the power performance of my truck. I am also interested in efficiency.

[06MonteSS]

the fuel trims are used by the ECM to gauge how much fuel to apply when driving....

the predator doesn't calculate that info - that's all stuff done by GM's ECM... the predator just displays the parameter values...

if ltft's are positive, that means you're lean and the ECM is adding fuel... if your ltft's are negative, that means you're rich and the ECM is subtracting fuel...

[mikel]

You need a wideband A/F meter.....

[HARLEY65]

Mike with regards to the LTFT's would you calculate the same with either the
87 tune or the 93tune?

[HARLEY65]

Mike with regards to the LTFT's would you calculate the same with either the
87 tune or the 93tune?

[mikel]

Yes, they'll be pretty much the same.

Thanks