What happens to the calculated figures when injectors are changed to larger than stock (22lb to 25lb)? Are the readings still accurate? Seems to me I read somewhere that the chip has to be re-burned to ensure accuracy. Would readings be more than actual or less if chip is left stock?

 

Im not sure this can be corrected with a chip. I change injectors and about everything else on my car at the same time. I did notice that TPS settings seem to affect the mpg readout. If its not too far off you may try it. Mine says 25 mpg and I really get 22. :chevy

 

Is the how-to in the "tools" section. I still can't figure out waht the size of the injectors has to do with a function that has to calculate fuel used through a distance. :crazy:

 

The mileage calculations in the computer (ECM) are basically based on an algorithm that compares the injector pulse width to the vehicle speed (instant MPG) or miles traveled (average MPG). This is based on the stock fuel pressure (35-45 PSI).

When larger capacity injectors (25 lb vs stock 22 lb) are installed, the computer will adjust the pulse width to maintain a 14.7:1 air-fuel ratio.
Because the larger injectors would allow more fuel to be put into the engine without the equivalent additional air being introduced, the computer cuts back the injector pulse width. The computer also senses in its "mind" that less fuel is being used and will give a MPG reading that is higher than reality!

25 lb vs. 22 lb should give about a 12% change in MPG readings.

So this means where the old stock injectors may have had a an Instant MPG at a steady 60 mph on a level road of 26 MPG, it will be with the higher capacity injectors, 29 mpg or even higher. Average MPG would be similarly affected.

Can this be corrected? Yes-with a modified chip. Another way is to reduce the fuel pressure slightly, BUT this negatively effects the spray pattern of the injectors. Higher pressure equals a "finer" spray pattern, atomization and potentially fuel burn.

 

Thanks for the lucid explanation, Wildride! :)

The car is running rich right now, an adjustable fuel pressure regulator is on its way.

Do you think that driveability will be adversely affected if I reduce pressure to where I've leaned it out as necessary?

 

Even if you deviate from stock fuel pressure the calculations will be off. :yesnod: