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Can I dump FI on 98 4.0 for a carb?

CFD

NAXJA Forum User
Location
CA
I'm new to the board and hope y'all can give me some of the same advice I've seen you've given to others. I've got a tired old 258 with a carb. I just lucked into a 4.0 from a wrecked 1998 Grand Cherokee. I want to swap it into my unit, but there's no way I'm ever going to get all the computer crap hooked up. Even my regular mechanic who normally will tackle anything doesn't want any part of it. So my question is this. Since I don't have any smog laws to worry about, what would be the pitfalls of dumping the FI and going with a carb. And if I do, what other mods should I make (I'm open to doing a cam, but don't want to tear down the engine beyond that). Also, I'm more interested in street performance, so I don't need all the low end grunt. I was thinking of a higher lift cam (any thoughts). Also, how much carb could I handle with this set up? And most importantly, if I go with the right carb, cam, and headers, how will my HP and torque compare to the factory 4.0 HO with the FI? Also, I was planning on using the trans from the 98. May be a dumb question, but will dumping the computer cause me any problems there? Look forward to hearing all your thoughts as I need to get this thing going asap. Thanks...
 
First, what type of vehicle is this going into? AN XJ, YJ, CJ? Also, I think the tranny is computer controlled. Might check on that, I'm more into the manual trannies.
Tom
 
This is very bad idea. Get a factory service manual, the wiring is very simple with proper diagrams. Much less complex than late model CJ carb setups or early Renix stuff.

I can't imagine ever running a carbuerated vehicle, the performance loss would be horrible in my mind, mileage wise as well as power wise.

And yes, the auto trans works in conjunction with the fuel injection.

Stick with the FI, your fellow Californian's lungs will thank you for the improvement in air quality.

CRASH

CFD said:
I'm new to the board and hope y'all can give me some of the same advice I've seen you've given to others. I've got a tired old 258 with a carb. I just lucked into a 4.0 from a wrecked 1998 Grand Cherokee. I want to swap it into my unit, but there's no way I'm ever going to get all the computer crap hooked up. Even my regular mechanic who normally will tackle anything doesn't want any part of it. So my question is this. Since I don't have any smog laws to worry about, what would be the pitfalls of dumping the FI and going with a carb. And if I do, what other mods should I make (I'm open to doing a cam, but don't want to tear down the engine beyond that). Also, I'm more interested in street performance, so I don't need all the low end grunt. I was thinking of a higher lift cam (any thoughts). Also, how much carb could I handle with this set up? And most importantly, if I go with the right carb, cam, and headers, how will my HP and torque compare to the factory 4.0 HO with the FI? Also, I was planning on using the trans from the 98. May be a dumb question, but will dumping the computer cause me any problems there? Look forward to hearing all your thoughts as I need to get this thing going asap. Thanks...
 
You could possibly mate up the 258 head, intake, carb, exhaust manifold, etc. to the 4.0 liter block, but I doubt it would make any more power than what you already have. And the trannies in the ZJ aren't all that great compared to the XJ units, both of which are computer controlled. You'd have a much more driveable setup if you research the wiring options more and stick with the FI system.

Edit: Crash beat me by a nose. :mad:
 
The 258 head is worst than the Renix head. Most swap on a 4.0L head onto the 258 for an increase of power. If your swapping this into a CJ or early YJ, then get the wiring for a Later YJ or TJ. I'd go with an HO wiring as only one O2 sensor. The problem might be with your 98 head as the 91-95's had an extra sensor in the head, so that hole wouldn't be in your 98 head. So maybe a 96-98 wiring harness might be best.
Tom
 
Sooo.... You got a : free 4.2 crank + free 4.0 block = extra cash saved from getting the free crank - smog restrictions x lack of attention to fuel mileage = one 300hp 4.6l stroker. You already have a lot of the parts.

I don't see how you would get the 4.0 manifold to accept the carb. The sensor hookup would not be too dificult with your 98 as there are not a lot of parts to worry about if you have the whole harness. Its just basic wiring, mostly just in the engine compartment where the comp is plus if its a cj, the dash nightmare is not too bad. I am assuming this is some sort of CJ since you said there is no smog. I don't know where you take your rig but the FI would be better for high altitude and offroading at steep angles that carbs don't like. If its an older CJ I'd keep it manual tranny so I would find, that guy said, an earlier YJ or TJ with manual tranny, 'puter and harness. By the way, you can get an 02 sensor eliminator that gives your computer the right numbers for the second sensor that watches the cat.
 
You could - I think Clifford has a manifold that will do what you need, and a good machinist should be able to make an adapter for you if not. If you do, can I talk you out of the control elecrinics so I can work up a bench sim?

Having said that, why? The FI will serve you much better than the carburettor, and I think you'll have trouble setting up the ignition without the electronics. You could possibly adapt the GM DIS from a V6 to the 4.0 (and idea I'm toying with - for when I leave California (damn!)) but it might still expect some FI signalling for injection timing. Most of the electronics from that you can probably get to fit under the hood...

5-90
 
Theres always stand alone FI systems, doubt theres a 4.0 application. Im sure you arent looking to spend that kind of money.
 
OK, you can do this and come away with something decent but it will cost you at the pump and right away to do it right. You will need a performance AMC six cylinder distributer or a gm HEI that a few people I know like to put on there 258's. You will also need an intake manifold from a 258 and you will need grind off the locator dowls to get it to work if it will at all, Clifford makes a nice 4bb manifold. Or you can build a spacer to fit it to your existing manifold. You will obviously need a good 4bb carb, I like webbers but if angles aren't a concern for you you have a lot of options. You will also need to talk to brettm about a manual controll for your aw4 that would be nice for the street anyway. That with a cam puts you probably around $500. I can get a wiring harness and all the sensors from the junk yard for around $20. Youre time and money are better spent with a weekend of wiring. If you want to do it, go for it and report back.
 
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