What is the benafit of upgrading injectors ... have a 99 4.0l and was thing of upgrading to get better gas milage

 

Replacing your worn injectors can net you better gas mileage. There is speculation that the better atomization from the four-hole style injectors causes the fuel to burn more efficiently/smoothly.

I ran my stock injectors into the ground, and when I was having misfire codes and an injector that would stop working every time I restarted the Jeep while warm, I finally replaced them. Yes, mileage got a little bit better, but the Jeep ran SO much more smoothly it was night and day.

I ended up going with Precision Auto Injectors, and never had a reason to look back. Wojtek is a good guy and will help you figure out exactly what you need.

 

Thinking about upgrading to the 703's? I've heard people get anywhere from .5 mpg gain to a whopping 5 mpg gain. All depends on your rig. Lift height has a lot to do with it. Better throttle response and smoother idle is pretty much a general consensus. But I achieved the same thing with seafoam through a vacuum line and a little deep creep in the TB

 

ok so 703 or 784 ???

 

For a 99 you need 784's.

 

Unless you flash the ECM it doesn't make much difference with the newer models, OBD2, because the ECM just adjust them to stock parameters.

 

So, how do I get the computer re-flashed in my 99 if I put in the 784's?

 

Read the first page of the write up link in my signature. Last few steps tell you how to reset the ECU.

 

Thanks, great info there!

 

Just for the record, since you're asking, I put 784's in my 00 XJ, and have noticed much better/immediate throttle response. It's very snappy now, but not annoyingly so - you just don't need to put your foot into it as much as you used to.

Fuel mileage pretty much stayed the same.