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post #1 of (permalink) Old 06-06-2001, 09:21 AM Thread Starter
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4.0 SWAP Fuel Rails????????

I was wondering how easy it is to change the fuel rail on the Jeep 4.0 engines. Most of the 4.0 swaps suggest using 91-95 4.0 engines because of the fuel rail. Later model Jeeps have the regulator and filter in the tank instead of on the rail. I am looking for a 4.0 for my Scrambler and I am having better luck with newer engines. How difficult is it to change the fuel rail? Does anyone know if the rails are interchangeable between all model years?

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post #2 of (permalink) Old 06-06-2001, 01:10 PM Thread Starter
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Re: 4.0 SWAP Fuel Rails????????

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post #3 of (permalink) Old 06-06-2001, 01:21 PM
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Re: 4.0 SWAP Fuel Rails????????

I don't know what year, but C/D did away with the return line back to the tank so therefore there is no fuel regulator on these engines. Can't seem to help much on the swapable years, I do know they will, just not exactly what years. What exactly are you looking to swap around? Later.

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post #4 of (permalink) Old 06-06-2001, 01:28 PM Thread Starter
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Re: 4.0 SWAP Fuel Rails????????

I want to swap a '91-'95 rail onto a '96-'01. That way I can use the regulator and return line on the older style rail.

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post #5 of (permalink) Old 06-06-2001, 05:00 PM
 
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Re: 4.0 SWAP Fuel Rails????????

I am in that exact boat. I have a 2000 Cherokee 4.0 that I got a good deal on. It's sitting in my wife's Scrambler now, but it's just a rollin chassis now. I might change the rail, or use an external regulator. Either way should work, but I haven't had much luck trying to find a proper aftermarket regulator. (haven't looked that hard yet) Also, it *might* be possible to get the factory pump/regulator assembly to work in the existing tank, or perform some mods to make it work...
Bob in Ma

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post #6 of (permalink) Old 06-06-2001, 07:41 PM
 
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Re: 4.0 SWAP Fuel Rails????????

Count me as another going through this.
I found a guy with a blown '97 and have bargained for his head, intake & exhaust manifold, throttle body and injectors.
Maybe I should have snatched his computer and harness but I've heard these get way more involved with the gauges and such so I've been thinking I'd retro fit MPI kit stuff from Hesco instead of having to deal with it. Any thoughts on this ??
A guy really into Mopar 'tricks' wrote me not too long ago that the newer style intake manifolds had much better flow chariteristics so I presumed one of these would swap into the older ('91-'96)FI set up ... I'll check on this.
Keep this thread going, OK!

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post #7 of (permalink) Old 06-06-2001, 11:25 PM
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Re: 4.0 SWAP Fuel Rails????????

The '91-'95 engines use the older SBEC computer, with the 60 pin connector. These all use a 35 to 42 lb. system with a return line and a vacuum controlled fuel pressure regulator. The vacuum control on the regulator is used to maintain a constant differential across the injector. If you had 16 inches of vacuum pulling fuel from the injector, with 35 lbs. of pressure behind it, it would deliver the same amount of fuel as no vacuum in the engine, and 42 lbs. of pressure behind it, with the same injector opening time.

The newer,'96 and up, systems use a much faster JTEC computer. The JTEC controllers use three 42 pin connectors. This computer has the ability to sense manifold vacuum from the MAP sensor, and make it's own corrections. These systems use a fixed 50 lb. fuel rail, with no return line. The biggest dis-advantage of swapping the JTEC system is the "check engine" light driver. There is none in the JTEC systems, it is all controlled by two wires on the CCD bus. In fact, every guage in the instrument cluster is controlled by these two wires. The oil pressure, vehicle speed, tach, coolant temp, odometer, even the fuel level. There are advantages and dis-advantages to this system. If you were to hook up the new style dash, it would be a breeze to wire, and you wouldn't have to fool around with a mechanical speedo cable. The drawback is the amount of wires, and the mess in the relay center.

The fuel rails between the two will easily swap over, I think 3 screws. If you have plans on using a newer engine with an older SBEC controller, you should swap to the old style rail and regulator. Another downside is the different style plugs on the sensors. You would have to change act, iac, tps, map, etc or the wire connectors. I believe the values are all the same, but the newer systems use a 5 volt vref instead of 8 volts.

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post #8 of (permalink) Old 06-07-2001, 05:21 AM
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Re: 4.0 SWAP Fuel Rails????????

Its 4 screws holding the fuel rail on the newer ones. I had my buddy come over and we lined his new, beside my older CJ with the MPI and I didn't see why you couldn't take the older and combine it with the newer engine. Matter of fact it looked like it would be rather easy. Hope this helps out. Later.


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post #9 of (permalink) Old 06-07-2001, 07:15 AM Thread Starter
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Re: 4.0 SWAP Fuel Rails????????

DORFS,
The do you think it would be better to switch fuel rails and contollers to the SBEC system or would it be better to build a filter/pump/regulator combination like the stock JTEC setup? Has anyone thought of just getting a complete TJ gas tank and putting it in a CJ?

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post #10 of (permalink) Old 06-07-2001, 09:34 AM
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Re: 4.0 SWAP Fuel Rails????????

After looking side by side last night it would be easier to swap the SBEC system to the newer engine. Hope this helps out.

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