I have a fresh 4.0 I just rebuilt and other than boring it .020 over, the only other change I’ve made so far is upgrading to 784 injectors.
The motor runs beautifully (other than a super mild lifter tick I’m going to address this week.) but one thing I’m dealing with is my long term fuel trim. I expected it to be trimmed back due to the higher flow from the 784 injectors, but I’m seeing consistent numbers in the -28% range. Short term trims are +/- 3% and the O2 sensor cycles cleanly between .2-.8 volts so the system is operating within parameters.
I’m adding a 62mm throttle body, cold air intake, Banks SS header and 2.5 inch SS exhaust, cat and muffler all the way back as soon as I have the time.
With the +.020 bore and all the above I’m thinking the higher air flow (although minimal) will help pull the fuel trims closer to zero, but I still don’t think I will get more than 4 or 5 points improvement.
Has anyone else with a stock motor that added 784 injectors looked at their fuel trims and seen these kind of numbers?

I would like to find a set of injectors that were 4/8 or 12 hole with a flow rate lower that that of the 784’s and a litter closer to stock flow rates. Does anyone know what injectors would be a little closer to stock flow rates?

Thanks in advance,
Michael

 

Off the top of my head I'd say Bosch 280156161 but you'll have to dig up the flow rates.

 

161’s actually flow more than the 784’s at 49 psi.

 

Just wanted to say I run the 161 in my 2000 stock XJ with the 4.0 and love them. I have not checked the fuel trim but think my Torque app can show them. If I get the chance I'll hook up a see what it shows.

 

country2, did you ever get a look at those fuel trims?

Still curious.

 

Nope forgot all about it. My sons has it now I'll see if I can get a hold of it Sunday and see if I can get them.

 

Those trim numbers are way out. I suspect the wrong injectors?

 

I am running 161 12 holes in my 2000 with acceptable fuel trims. I will double check them my next day off to confirm that they are still correct. PM me if you are looking for a refurbished set.

 

Hey finally got a hold of the jeep and ran the torque pro app and both of my long and short varied from around -7.4 to -11.4 going down the road at 65mph @2000 rpms.