98' 4.0 conversion to a carb

N

nrwphoto

NAXJA Forum User
Location
Appleton, WI
I have a 98' XJ that has had electrical gremlins in the interior wiring for years. I also have a lack of power and mpg compared to when I first bought it. I have had it into several reputable mechanics and even had the computer reflashed a couple of months ago with no luck. Because I have so much invested in suspension, steering, axles, brand new tires and misc new parts when I decided to move from AZ to MT I loaded the Jeep on a trailer and drug it up here. When I backed it off the trailer I could smell a hot electrical short. Well now it kills the battery in hours and you can pull all the relays and fuses out of the engine control box under the hood and various spots on the motor (CC module, fuel pump and a wonderful buzzing from the bottom side of the fuse box) still have power! :gonnablow::gee::flamemad::huh:

So after letting it sit for a couple of months not wanting to take a loss on all the parts and really not wanting to swap out the whole wiring harness. I am beginning to wonder if I can clear out a bunch of sensors and wires on the engine and convert it to a carb setup. I don't have to worry about emissions/inspections up here so that is no problem. I have read about using a 4.2 intake, Holley or Weber carb, fuel pressure regulator (5psi?) and HEI distributor. Would I need anything else?

Also would the AW4 and gauges (speed, tach, temp, oil pressure) still work if I pull the FI system? Obviously I would leave the above sensors on the motor.
 
To me, the benefit of carb would be less appealing than just pulling the engine wiring harness and replacing it.

Its obvious you have a short somewhere, but I don't think swapping to a carb setup is a great idea. Here is why:

1. Tuning will be iffy. You live in a part of the country where temps will range from fairly warm in the summer to down right bone chilling cold in the winter. Carbs don't like that too much.
2. If you offroad at all, you will now have to worry about the carb getting enough fuel on off-camber events. You can get around that with higher fuel pressure and some voodoo, but nothing will compare to a good FI system.
3. The cost of doing a swap. You will need to find old parts and outdated technology, as well as change the way fuel is delivered. Not to mention that carb parts are becoming rare.
4. The price of a good "used" harness will be much much cheaper than dealing with the cost and sourcing of a good carb setup.

5. You will more than likely need something to control the trans. There are sensors on the motor that will be deleted with a carb setup, that you need for the AW4.

You are welcome to do as you wish, of course. But if it were me, I would learn to use a voltmeter (not that you don't know how to), get a wiring diagram, and look for complete 4.0 wiring harnesses from Jeep or source a used one. I know that a used wiring harness can be had for stupid cheap, but it may be worth going to Mopar and seeing what they will run.

Just my .02. Good luck and I truly hope you figure it out.
 
Repairs with good used parts will take less time and cost less than trying to convert to a carb. The instruments will not work, and you will have to shift the AW-4 manually into every gear.
 
And if you don't FIND the problem and FIX it, there's no guarantee that even after going thru the hassle of the conversion to a carb, you won't still have the same problem.
 
Suspsnsion, steering, axles, tires and misc will all swap over to a new chassis if you can't figure the wiring out.
 
Ever carb based rig converts to FI for a reason. Fix your wiring it will be easier
 
IllianaXJ said:
Suspsnsion, steering, axles, tires and misc will all swap over to a new chassis if you can't figure the wiring out.
Click to expand...

thesteveyo said:
No kidding. I bet it would be quicker and simpler (and cheaper) to just swap your upgrades to a clean, known-running Jeep.
Click to expand...

This was actually the original decision. Find a clean XJ with a 5 spd and manual windows and locks to swap over to. Just haven't had any luck finding one. I have a little 87' Samurai that is carbed and the idea popped into my mind. As far as FI being better... I am a fairly strong proponent of mechanical things... carbs. True FI will self adjust for elevation and temp. But if you know what you are doing with a carb it can run just as well or better than FI it just takes more attention to keep it in optimum tune. Plus I just like fewer parts and simple when possible. But that is the important thing (when possible)

Thanks for the input everyone.
 
nrwphoto said:
True FI will self adjust for elevation and temp. But if you know what you are doing with a carb it can run just as well or better than FI it just takes more attention to keep it in optimum tune.
Click to expand...

This is the silliest thing I have *ever* read on NAXJA.
 
How about you just buy a good harness from me for less than you'd spend on a carb and you'll be good to go.

Which harness do you need? I have 4 98 parts Jeeps sitting in my yard. 3 of which have complete wiring harnesses
 
Converting to a carb to cure a short is roughly analogous to committing hari-kari over a stomach ache. Sure, you may have removed the problem but now you have a pile of steaming guts and fecal matter to deal with.

Carbs have every known disadvantage when compared to EFI *except* that if you grew up working on carbs and can't be bothered to learn new things, hey, you can fix a carb yourself! Which is great, because you'll have to.

Most saturdays I go to Cars & Coffee, a mostly-old-guys crowd of classic iron. Really nice stuff, mostly still carbureted. Y'know how often I see old guys standing around and heckling each other's cars that don't start right, or on the side of the road? It's got-damned undignified. Engine in my truck? 8 injectors, 8 coils. One goes bad every 150,000 miles or so, I drive to the auto parts store & pull the code & replace the part. But hey, fix your Jeep how you want.
 
Clifford makes a 4 barrel intake that will bolt up then a holly 390. Purchased new you will be in $700.
I yea then add an old school distributor and coil.
Can be done, but depending on goals there may be better solutions
Edit Clifford not Cleveland
 
Last edited:
Agreed that you're going to regret this. I have an off-road carb on my 350 conversion xj, and it stalled out a form times on the trail this weekend. I just pulled the trigger on a Holley termonator efi.
 
Lowrange2 said:
lol, and now you're back to the the power of a 4.0.
Click to expand...

missing that one...

I'm back to the *reliability* of the 4.0.... I had it beat on power by a large margin the first day it was in :-)
 
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