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Lots of Mods, poor fuel economy... searched

Overdriven

NAXJA Member #1020
Location
Dayton, Ohio
I've been fighting 10 -11 mpg for a while now and can't seem to get my act strait. Will someone look at my recipe for disaster and pescribe an antidote.

88 XJ 4.0 Renix, AW4, NP231 - Starting point.
Still running the renix computer system

Motor - swapped in a 98 4.0, Added a coolant temp sensor to the block to control the Temp guage, and get the readings for the computer from the water neck.

Intake - 92 intake and fuel rail, HO throttle body (using renix sensors and spacers) stock Air box with 3" PVC snorkle. Running 21lb Ford mustang 5.0 fuel injectors.

Exhaust - Pacesetter Header, High flow cat, cherry bomb glasspack, dual exhaust from cherrybomb out.

GDI 3 core radiator, (swapped to open system) - stock mech and elec fan.

Jeep has been running rich for as long as I can remember. I've considered swapping back to the renix system or swapping to the HO computer system... and I've read many posts on MAP adjustment, but I dont think that's a fix.

I've swapped out the O2 sensor, plan on boring out the throttle body... but I"m open to advice.
Thanks.
 
Axles,tires,wheels,and gears?
 
well ill be honest, i prob wont have any answers for you
but didnt the renix system have a different fuel rail and injectors than the HO, just thinking that there may be a problem with the renix comp system talking to the new injectors/rail ?

also, possibly a bad MAT sensor?, if its sensing colder air, possibly throwing off the fuel system?

just some thoughts
ryan
 
Right, I was focused on the engine area...

Chopped body, caged, 35" Truxus MT's, steel wheels, 4.56's, Detroit rear, lockrite front, 30 front, 44 rear...

Here's a recent pic.
HatcherPassWeekend5-08067.jpg
 
I'm just guessing...but it might have something to do with driving a brick down the road. Because, you realize that is essentially what you have right now, right?

~Scott
 
unless you get your computer mapped for bigger injectors you'll be dumping in extra fuel all the time.

Not sure how those 21lb mustang injectors compare to the stock ones, but if they're a higher delivery rate, which I think they are, then that is probably your problem. That is of course assuming you didn't get the computer remapped for those injectors.
 
unless you get your computer mapped for bigger injectors you'll be dumping in extra fuel all the time.

Not sure how those 21lb mustang injectors compare to the stock ones, but if they're a higher delivery rate, which I think they are, then that is probably your problem. That is of course assuming you didn't get the computer remapped for those injectors.

Not 100% sure but I think the HO motors (which he swapped to) are already running the 21lb injectors. Where do you have your IAT sensor at?
 
The 21lb injectors are supposed to atomoize the fuel better than stock injectors. I know the renix were 18lb stock and the HO was 21lb. The fuel rail and regulator are from a HO.

AJ, as far as where... Do you mean physical location? it's in the stock hole in the intake manifold behind the throttle body.

or are you looking for a readings I'm getting from in?
 
I'm just guessing...but it might have something to do with driving a brick down the road. Because, you realize that is essentially what you have right now, right?

~Scott

Yeah, I know that much. I'm not expecting above 20, but I'd like to see at least mid teens again. Stock, my XJ got 21.

Mostly, I want to quit running so rich so I don't clog up my exhaust, cat, injectors, etc.
 
I think your best bet would be to upgrade to HO comp. and sensors and then look into an adjustable MAP to get the A/F ratio set to where it should be.
 
if you're still using the renix computers then your injectors are most likely the issue. The computer determines what duty cycle the injectors are spraying at, determined by the other engine sensors. IIRC, the fuel pressure is the same between the renix and HO, so putting an injector in that runs 3lb more than stock, you're going to be getting more fuel than you need because the computer assumes you're running an 18lb injector. So if the computer is calling for an 80% duty cycle and a specific RPM and load from a 18 lb injector, and you're running 80% from a 21lb injector, obviously you're getting more fuel.

Remap the ECU or swap to the HO unit. That would be my suggestion to get things goin right.
 
first, beautifull photo!
2nd...
I'm just guessing...but it might have something to do with driving a brick down the road. Because, you realize that is essentially what you have right now, right?

~Scott
i would dissagree, putting a cage, bumpers and 35's on a jeep does not transform it into a brick! it would be differant if he was running 1-tons and 40's @ 8"
 
if you're still using the renix computers then your injectors are most likely the issue. The computer determines what duty cycle the injectors are spraying at, determined by the other engine sensors. IIRC, the fuel pressure is the same between the renix and HO, so putting an injector in that runs 3lb more than stock, you're going to be getting more fuel than you need because the computer assumes you're running an 18lb injector.
I agree with that diagnosis. If you don't want to change computer and sensors, find new injectors that match your computer.
 
I've got a set of injectors that match up to the HO 92 intake but I don't have any renix injectors on hand. Need to keep a look out for them I guess.
Thanks for the advice. I'll chime back in when I swap injectors.

I'm researching swapping the computer system since I'd like to take advantage of the HO sensors and computer. I've got too much time in this XJ to swap it all over to a new rig.

anybody have any links to computer swaps? Renix to HO?
 
I went with an adjustable map sensor and regained much of my mpg's back. I am running the ford "red tops" for injectors, which are close to 30lbs. I still need to get my computer redone, but I am averaging 17 - 19 mpg's. Mind you, I have no interior, no doors and running 32's on 4.56 gears.

anyone know where you can get the ecu remapped for bigger injectors? I have no clue so far.
 
I would have just said tough it out, you are running 35's. You can try a map adjuster, but be careful not to lean it too much. In the end you are still driving a truck with a lot of wind resistance since it is a lifter brick, heavier from the cage and armor, and with extra rolling resistance with 35's and two lockers.
 
That is what i would say, learning from all my problems it has to be in the fuel control area. But you must remember when you start searching for performance you loose sight of fuel economy VERY fast especially when it happens to look like a brick.
 
I agree with the fuel injectors being a bit large. I kinda skimmed the thread but did you say why you went with the larger injectors. More power/cheap swap? Also you can also get rid of the mechanical fan for an all electric set up for an extra 1mpg or so.
 
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