4-hole injector flow rate question

hi ,

I have purchased some ford 4-hole injectors for my 01 4.0L XJ. I know this topic has been thoroughly discussed but I haven't found anything pertaining to this in the searches I've made at .

From what I know, the 01's have their fuel rail set at 49PSI and the injectors itself have a static flow rate at 22.5lb/hr (correct me if I'm wrong).

The injectors I purchased I was told from the seller work fine in my model year XJ, but a quick google search of the part number shows them at a 16lb/hr injector at 43PSI. Even when adjusted to the XJ's 49PSI rail, it brings it nowhere close to the factory 22.5lb/hr flow rate (18.02lb/hr according to what I calculated at 49PSI)

My question is:

1) theres a 4.5lb/hr difference between the two injectors. I'm assuming this will cause my jeep to run lean? or will the o2 sensor be able to scale and adjust for this correctly?

2) is it safe to run? should I add and adjustable FPR and raise the rail pressure to try compensate (would have to run the rail at 58-60psi)? I know even w/ the factory injectors the XJ's run rich past 3k RPM. I dont have any way to measure AFR on this vehicle nor do I want to install a wideband AFR gauge to monitor this.

Thanks in advance for any input!

Injector flow rate (lb/hr) = [Expected HP x 0.5 (BSFC)] / [no. of cylinders x 0.8 (injector duty cycle)]

The actual injector flow rate from each injector depends on the fuel pressure (FP) in the injector rail. Most injectors have rated flows at 43.5psi fuel pressure. The actual flow rate from each injector is:

Actual injector flow rate = Rated injector flow rate at 43.5psi x square root of (FP/43.5)

From jeep4.0perfomance

831_xj said:

Injector flow rate (lb/hr) = [Expected HP x 0.5 (BSFC)] / [no. of cylinders x 0.8 (injector duty cycle)]

The actual injector flow rate from each injector depends on the fuel pressure (FP) in the injector rail. Most injectors have rated flows at 43.5psi fuel pressure. The actual flow rate from each injector is:

Actual injector flow rate = Rated injector flow rate at 43.5psi x square root of (FP/43.5)

From jeep4.0perfomance

Click to expand...

Yes, the values i've given are comparing the injectors adjusted values at the 49PSI fuel pressure on the XJ rail. I just want to know if the 4.5lb/hr difference will be significant enough to cause a lean condition, or if the o2 sensor will compensate for it.

What is the part # on the injectors that you bought?

What color are they?

cal said:

What is the part # on the injectors that you bought?

What color are they?

Click to expand...

YF1E-F4C

witchhunter is the only place where I found injector info for it on (180cc/min @ 43.5psi)

180cc/min @ the XJ fuel rail at 49 PSI yields 191.041cc/min.

stock 2001 XJ injector flow rate: 236 cc
the injectors i have: 191.041 cc

I know o2 sensors can adjust to a certain extent, but I am new to jeeps and not entirely sure how much the o2 sensors actually can compensate for. I'm assuming if the jeep does run lean it will throw a code?

hmmm...coming from the world of forced induction cars, thats a big no no....The O2 sensor can compensate a little, but having the cc be that much less, at full throttle I feel like you are probably going to be running lean.

Try and find the duty cycle at 100% throttle for the stock injectors, and see how many cc it uses, then compare that to the cc of the new injectors to see if they can spray enough fuel. (Does that make sense?) Also, I believe it is not recommended to have duty cycle above 80% i think? I could be wrong, don't quote me on that.

Another thing to think about, is the fuel is going to be burning much better with the 4 hole, and that could be putting you in the clear.

i would never install an injector that has a lower flow rating than stock. that would be just as bad(or worse-like leaning out under a hard load/high rpm) than installing injectors that are too high a rate(obviously the ecu can dial down the fuel a little if they're a tad oversized).

Hellbent said:

i would never install an injector that has a lower flow rating than stock. that would be just as bad(or worse-like leaning out under a hard load/high rpm) than installing injectors that are too high a rate(obviously the ecu can dial down the fuel a little if they're a tad oversized).

Click to expand...

The flow rates on injectors are max flow rates. Its ok to go bigger as long as you have the right tune to let the car know the injector latencies. The car isnt always squirting in 200+ cc of fuel, it varies by rpm. Lower flow rates can cause issues, but the OP needs to look and see what the stock duty cycle is at 100% throttle to figure out how many cc/min the car uses at full throttle. Im assuming its around 80% of 236cc.

erykv1 said:

YF1E-F4C

witchhunter is the only place where I found injector info for it on (180cc/min @ 43.5psi)

180cc/min @ the XJ fuel rail at 49 PSI yields 191.041cc/min.

stock 2001 XJ injector flow rate: 236 cc
the injectors i have: 191.041 cc

I know o2 sensors can adjust to a certain extent, but I am new to jeeps and not entirely sure how much the o2 sensors actually can compensate for. I'm assuming if the jeep does run lean it will throw a code?

Click to expand...

that is the wrong injector. throw them out, throw them on craigslist, just keep them away from your 4.0.

i agree. i was speaking specifically just about a stock-ish jeep running a stock ecu.

XJ_Rudolph said:

The flow rates on injectors are max flow rates. Its ok t! o go bigger as long as you have the right tune to let the car know the injector latencies. The car isnt always squirting in 200+ cc of fuel, it varies by rpm. Lower flow rates can cause issues, but the OP needs to look and see what the stock duty cycle is at 100% throttle to figure out how many cc/min the car uses at full throttle. Im assuming its around 80% of 236cc.

Click to expand...