Hi everyone, I am building a 1994 mid performance 4.0l and I have run into another issue that I can't find the fix for. I think I have went beyond what the OEM injectors can give, do any of you have a solution for this? Thanks all.

 

Injectors are rated in Pounds Per hour, that's how many pounds of gasoline it can flow in 1 hour, because air/fuel mix is by weight, 14.7:1, so 14.7 pounds of air for every 1 pound of gasoline
Stock 4.0l 1990-2000 were 14 pounds an hour so good up to about 190HP

Simple way to decide what size injectors to run is to "guesstimate" what horse power you will end up with, and multiply that by 0.5 then divide by number of injectors

Say your V6 4.0l will have 300HP
300 X 0.5 = 150
150 / 6 injectors = 25
So 24lb/hr injector would be fine to use

Say you expect 250HP
250 x 0.5 = 125
125 / 6 = 20.8
So 21lb/hr injectors would be fine

Too big of an injector will cause issue with your computer
Too small will as well
These are NOT LIKE JETS in a carb

Computer calculates injector open time based on several things, one of them being the injectors "size", i.e. how much fuel flows out when this "size" injector is opened for say 100ms(milliseconds)
It has a 15% fudge factor before it will set Lean or Rich codes which happens at 20%

You have a MAF system so its adaptable to upgrades in horsepower, computer doesn't care about that, its sole purpose is to make the right air/fuel mix

Cold start might be an issue at first with bigger injectors because the computer has to run thru a few drive cycles to store "long term fuel trims" to offset Cold start factory fuel trims
But it will adapt to the new injector size

 

Thank you RonD that is a lot of useful information. My problem is I can't find any injectors other than OEM anywhere, I need a source to purchase the upgraded injectors.

 

Check 1998-2000 Ranger 3.0l Flex Fuel injectors, Motorcraft CM4889, they are 21lb/hr

The 2001 and up 4.0l injectors were 19lb/hr

 

Thank you again RonD, my son has ranger 3.0l so I will borrow one for fitment.