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post #1 of (permalink) Old 10-03-2006, 01:27 PM
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Convert a Fuel Injected XJ to Carburetion

I just bought a 1999 Cherokee XJ ( 2.5L 4 Cylinder with fuel injection/ 5 speed manual/ 4WD) I have owned many fuel injected vehicles and I dont like having all the additional sensors, devices and computers that come with them. More things to malfunction and leave you stranded and more difficulty in diagnosing engine problems. I enjoy tuning and modifying carburetors. I have been able to do quick improvizational carburetor repairs that got me home while being literaly "in the middle of nowhere" in the New Mexico desert or mountains, that would not have happened whith fuel injection.

I know some of the pro-fuel injection arguments, better mileage, no engine dieing on steep slopes ect but that doesnt change my opinion. Modifying the float bowl and choosing the best carburetor can improve engine performance on steep inclines, anyway I use my vehicles for off road recreation not hard core competion. This year I changed my 1978 CJ-7 (258 6 Cyl/T-150) to an early 70's Carter YF carb (not the infamous BBD)and low RPM torque is noticiably better, gas mileage is 25 MPG in city driving (Although acceleration on highway on-ramps isnt great). I ran the same engine with a Ford MC-2150 carb for 2 years and found a good increase in midrange power with a slight decrease in low RPM torque. Gas mileage was 17 in city driving.
Both of these carb conversions were relatively easy but provided very substantial changes in engine performance.

Could someone share some knowlege in how to best convert
the XJ to carb? Especialy when dealing with the computer controled ignition.
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post #2 of (permalink) Old 10-03-2006, 03:05 PM
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Re: Convert a Fuel Injected XJ to Carburetion

[ QUOTE ]
I just bought a 1999 Cherokee XJ ( 2.5L 4 Cylinder with fuel injection/ 5 speed manual/ 4WD) I have owned many fuel injected vehicles and I dont like having all the additional sensors, devices and computers that come with them because they work great. More things to improve power and milage and no need to diagnose engine problems. I enjoy wasting time tuning and modifying carburetors in a vain attempt in getting the engines to run nearly as well as fuel injected vehicles. I have had to do quick improvizational carburetor repairs that got me home while being literaly "in the middle of nowhere" in the New Mexico desert or mountains, that would not have been needed with fuel injection.

I know some of the pro-fuel injection arguments, better mileage, no engine dieing on steep slopes ect but that doesnt change my opinion. Modifying the float bowl and choosing the best carburetor can improve engine performance on steep inclines to the point where they almost even keep running, anyway I use my vehicles for off road recreation not hard core competion. This year I changed my horrible carb on my 1978 CJ-7 (258 6 Cyl/T-150) to a slightly less horrible early 70's Carter YF carb (not the infamous BBD)and low RPM torque is noticiably better, gas mileage is 25 MPG in city driving (Although acceleration on highway on-ramps isnt great). I ran the same engine with a Ford MC-2150 carb for 2 years and found a good increase in midrange power with a slight decrease in low RPM torque. Gas mileage was 17 in city driving.
Both of these carb conversions were relatively easy but provided very substantial changes in engine performance.

Could someone share some knowlege in how to best convert
the XJ to carb? Especialy when dealing with the computer controled ignition.

[/ QUOTE ]

fixed it for you.
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post #3 of (permalink) Old 10-03-2006, 03:29 PM
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Re: Convert a Fuel Injected XJ to Carburetion

Thinking out loud here.

1) You'll probably have to start just about from scratch with the carburetion. Use the FI manifold, plug uneeded holes and make an adapter to replace the air meter and accept the carb you decide to use. Since you're familiar with the YF maybe you could use it. It's as reliable and simple as an anvil. It's probably more than the 2.5 will need, but you should be able to jet it to compensate.

2) Since you're pretty much taking all the advanced electronics out, I wonder if you could install a distributor from a late 70's 258. You'll probably have to fiddle with the advance curve. You can use a V8 trigger wheel and grind half the spokes off. Then you can use HEI or a stock Autolite ignition module. A spare module will fit easily in the glove box.

3) What did you do to the YF to get such good mileage? I'm getting under 15 from mine, although that's at least partly due to a poor ignition timing curve.

4) Welcome to the board! That should be #1, but I'm in too much of a hurry to renumber everything. [img]/ubbthreads/images/graemlins/blush.gif[/img]
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post #4 of (permalink) Old 10-03-2006, 03:33 PM
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Re: Convert a Fuel Injected XJ to Carburetion

Besides all of the reasons you noted (better performance, no flooding, etc), the best reason is because "IT'S AGAINST THE LAW".

Modifing the emissions equipment on your vehicle is a violation of Federal law and most states laws. In some states you can get by with some changes....but to take a 99 that is OBDII and put on a carb?....not only will you stand a chance of getting a big ticket, you won't be able to legeally sell the jeep.

On a side note, I don't buy the reliability issue....I have been stranded more from carb problems than FI....I'll take FI any day over carbs.
post #5 of (permalink) Old 10-03-2006, 04:11 PM
 
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Re: Convert a Fuel Injected XJ to Carburetion

My advice would be if you really wanted a carbed XJ Cherokee, you can buy one on the used market for about $1000. 1984-85 2.5 XJs were carbureted and would be emissions legal.[img]/ubbthreads/images/graemlins/smile.gif[/img]
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post #6 of (permalink) Old 10-03-2006, 06:16 PM
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Re: Convert a Fuel Injected XJ to Carburetion

If you can muck about with a carb, you can learn fuel injection. It is not really that hard. Though true that EFI has single points of failure, it pays for itself in the long run... though you already know that... and are kickin' against the *****s... so to speak. You not only need to think about the engine modifications, but the fuel tank as well. That fuel pump throws out about 43psi of fuel to the fuel rail. The modification would require you to most likely fab a new fuel tank. I'd be surprised if a sender from an older tank would fit. Then what would you do for a fuel pump? The engine doesn't have a place for a retrofit. That means you're stuck with an early generation 12psi (or there abouts) electric fuel pump and a mechanical regulator to what ever carb you choose.

IMHO, you're far ahead of the game learning the EFI and squirreling a way a few sensors and a fuel pump in your spares kit. My EFI swap on my I6 has been much more reliable. It has let me down twice. The total cost for the repair was $12 and 45 minutes time to repair. When I say it let me down the fuel delivery did not fail. The engine still ran, but it ran rich. My fuel efficiency went from 13.5 mpg to 19.5 mpg. The modification paid for itself in 6 mos. of gas savings at 1996 fuel prices. I can't say that about a carb, any carb.

Do yourself a favor, and forget the carb swap. You're doing yourself a GREAT disservice. Get a good manual on the Jeep, learn the EFI system and ask questions, lots of questions. There's no doubt that there is a learning curve when you study EFI, but it's not insurmountable.

And the good part.. there's lots of guys that are dumber than you who've done it... so can you.

But, on the other hand, it's your Jeep, your dream, and your money. [img]/ubbthreads/images/graemlins/grin.gif[/img]
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post #7 of (permalink) Old 10-03-2006, 09:38 PM
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Re: Convert a Fuel Injected XJ to Carburetion

To each there own I guess...lol Look at the total cost in all the mods...carb, cpu, fuel tank, fuel pump, the time convetting the system, not to mention the LEGAL issues Its going to be cheeper to buy a carborated early XJ. I had one and I hated the carb system...not to mention it was WAY UNDERPOWERED. I think it would be a step backwards if you ask me..... BUT WAIT I have a carborated 2.5 in my 80 cj and Id love a fuel injection and you will have all the parts that you wont need...HUMMMMMMM. It sounds like a great Idea Go for it and sell...give me the parts you take off...better yet lets just swap compleate engines No mods for eater of us...LOL
but seariously I am not sure if its a good idea, but at least your willing to try somthing new or diffrent. Good luck and welcome to the board. and Keep us informed on this mod I am curious to hear a follow up, what it took, cost pros and cons.
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