24# injectors on nearly stock 4.0

[johnnyc]

With the 97+ model year the 4.0 got 23.8# injectors and distributorless ignition

2000-01 are the only years with distributorless ignition.

 

[NXJ]

From Dino's site.

Model Year, ...Part #, ......Colour, .....Fuel Pressure, ...Static Flow,
'87-'90, ........53003956, ...Black, ........39psi, .................18.6lb/hr
'91-'93, ........33007127, ...Brown, .......39psi, .................21.0lb/hr
'94-'95, ........53030343, ...Tan, ...........39psi, .................21.0lb/hr
'96-'99, ........53030778, ...Grey, .........49psi, .................23.2lb/hr
'00-'01, ........04854181, ...Blue tip, .....49psi, .................22.5lb/hr

So those flow ratings are at the given fuel rail pressure? Doesn't that mean that the 23.2#'s and 22.5#'s actually are weaker than the 21#'s and would put out like 18ish lbs/hr on a 39psi rail?

Also, doesn't the later XJ's get a returnless fuel system?

 

[wolfpackjeeper]

The later gens get no return line, correct. I think they would spray weaker, but I am not sure how much so. People start doing fuzzy math to figure it out, but pratically, the set of LT1s I have are spraying just about right on a system with a lot less pressure than they are designed for so the computer either compensates, or I just got lucky and they have minimal loss.

 

[gradon]

Yes, if you put the 23.2# or 22.5# on the 39psi rail, they would flow less than 21#(20.7 and 20.1). Also, the older fuel rails with the return lines are easier to put an adjustable fpr on.

 

[Talyn]

People start doing fuzzy math to figure it out,

Fuzzy math? Its a simple equation: new flow = squareroot ( new-pressure / old-pressure ) x old-flow-rate

 

[wolfpackjeeper]

Fuzzy math? Its a simple equation: new flow = squareroot ( new-pressure / old-pressure ) x old-flow-rate

yea, but I did not have the equation handy, so I just typed fuzzy math. Cause My memory was kinda fuzzy as to what I saved my performance calculations as.

 

[Talyn]

I have a book, "Auto math" that I refer to for equations that I don't use often enough to remember.. but I just happened to be using that one in the past few weeks.

 

[maybe2fast]

I have LT1 injectors on my 96.
The short term % is always around zero when I am driving with the scan tool
The long term % is always -13 to -15...

I am not sure what this means, but it idles great, starts nice, and drives great. But I am worried that the fuel trims are hurting my mpgs! I have a heavy foot but have NEVER gotten over 16mpg in this truck.

intake
muffler
LT1 injectors
1.5 lift and 30x9.5s

 

[gradon]

Long term means that your pcm has determined it needs to pull out 13-15% fuel(due to running rich w/ them lt1s). It has used the short term fuel trim over time to determine the long term fuel trims. If you would disconnect your battery and reset the pcm, your long term would reset to 0 and then you'd see more action on the short terms until it had enough data to come up with a long term.

 

[Archdukeferdinand]

With the 97+ model year the 4.0 got 23.8# injectors and distributorless ignition, I believe the 96 model year was the start of OBDII. The stock fuel / ignition can be used up to (I think) about 260 horsepower, after that injectors are needed, around 300 and the ignition holds you back some. Good luck getting 300 out of a 4.x without FI

My 97 has a dizzy...

I thought that started in '99. Could be just the last year like jonnyc said.

 

[yossarian19]

Yup, that was my bad.
Especially since I drive a 98.

 

[maybe2fast]

I wonder if the LT1s are hurting the mpgs? Runs really nice though!

 

[xjrider95]

okay, so what is needed to run the lt1s or the 24#s on a slightly modded 4.0 (intake, flowmasters) ??

 

[89xj]

okay, so what is needed to run the lt1s or the 24#s on a slightly modded 4.0 (intake, flowmasters) ??

what year xj?

 

[BBeach]

I dunno how much the jeep's can correct the fueling when in closed loop, but when you floor it, the vehicle goes into open loop and it won't rely on the o2 sensor anymore (which I believe would be the only thing to correct via the fuel trims). When WOT, in open loop you'll be running off the IAT, MAP and engine speed (amongst a few other small things). On that note, from what I'm guessing with the Jeep's is that it'll run off some tables and spray for what it thinks is the correct fuel injector pulse width (which under a higher flowrate will result in more fuel, which I'm unsure the ECU can correct for in open loop).

Does anyone know what ECU the jeep is? You should prolly invest in a wideband though. LC1's from Innovate are pretty decent.

 

[xjrider95]

what year xj?

oops its a 95 auto

 

[gradon]

Innovate has my thumbs up with the lm-2--it really is an excellent tool, and it is based off the technology from the lc-1.

 

[maybe2fast]

mine is a 96
intake
dynomax muffler
and the LT1 injectors
soon to have the 99+ intake

 

[XJLI]

whats the good word on running the LT1s or 5.0s in a 93 with 39 psi at the rail?

 

[maybe2fast]

my runs great but am asking some questions in some recent posts. check in street performance "just did the intake swap thread and in Modified ECM map question