Carb rebuild vs FI swap vs engine swap - Defender Source
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  #1  
Old July 12th, 2014, 07:44 PM
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Carb rebuild vs FI swap vs engine swap

A member of this forum is selling his complete 1994 3.9L of unknown mileage, including EFI, ECU and wiring. My 1986 3.5 L carburated V8 with 150K miles is in need of carb rebuilding. I am a little tight on funds right now and contemplating the following:

(1) Buy the complete engine setup, which will no doubt require a rebuild, and just swap out the EFI for now
(2) Once funds become available, rebuild the 3.9L, reinstall the EFI on it and swap my 3.5L out.

Now to the questions:

A) Is the EFI from the 3.9 to the 3.5 a straight bolt on? I realize that the wiring harness has to be swapped out as well, but otherwise, is this fairly straight forward?
B) Should I even bother with the EFI swap at this time, or just rebuild the carbs until the 3.9 is rebuilt and ready?
C) What am I missing here? I believe my tranny is the LT77. Can it handle the 3.9L?

All feedback and comments are appreciated.

Thank you - Samer
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  #2  
Old July 12th, 2014, 08:19 PM
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If you have a full defender setup with intake it will bolt in. You want all sensors including vehicle speed.
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  #3  
Old July 12th, 2014, 08:22 PM
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While yes you could bolt the injection to the 3.5 you would need to replace the tank with the later in tank pump that puts out 45 psi, run AN or similar fuel lines that can handle the pressure and then there's wiring up fuel injection in a truck that has a glass fuse fuse box. You would also need a transfer case with a VSS as John pointed out. Major undertaking.

Have you considered an edlebrock manifold and 4bbl carb ? Bolt on out of the box and go. I am not a fan of the zeniths and imo rebuilding them is an exercise in futility.
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  #4  
Old July 12th, 2014, 08:28 PM
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Yes you would need a high pressure pump. You can get an aftermarket one. Some regular fuel line from the pump rated for EFI pressures is fine.
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Old July 12th, 2014, 08:34 PM
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Douglas: Better words have never been uttered before! I asked this question in a thread (started by someone else) entitled "School me on the 4.2 L V8", to which I didn't get an answer. It surely sounds like the way to go.

Having done that, should I still buy the 3.9L and rebuild it when funds become available, to be swapped eventually? The seller is asking $300 + shipping for the whole shebang. BTW, it looks like my rig has had a fairly new gas tank installed, with a provision for an in tank fuel pump. I'm yet to investigate this, but I soon will.
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Old July 12th, 2014, 08:43 PM
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Its your money, as John point out there are corners you can cut like using pressure rated rubber fuel lines and hope they don't suffer any abrasion. Rover used steel tubing. I use steel reinforced flexible lines and factory tank and pumps, but as noted there are inline pumps that will do the job. Its a slippery slope and no one can tell you how to spend your money or where to stop. The 3.9 heads have bigger valves and are higher compression so you would get a bit more out of your 3.5 if you had the 3.9 ones cleaned up and a valve job with new guide seals done. But then there's the cam and lifters, and then there's the timing chain and gears that should be upgraded to a dual roller. You see it just keeps snow balling. Another upgrade for an early 3.5 is to ditch the crappy point and condensor lucas distributor (with the 12volt start-6 volt run so you don't burn up the points crap) for a later electronic one out of a fuel injected rrc or early disco.
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Old July 12th, 2014, 08:49 PM
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If I understand you correctly, you are suggesting upgrading the 3.5L with the 3.9L heads, valve job, etc. Did I misunderstand?

What I'm suggesting is a rebuild of the 3.9L EFI for an eventual swap, ditching the 3.5L.
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Old July 12th, 2014, 09:18 PM
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He is just talking of putting the EFI on for now. It works fine. I've done it. You need all of the stuff from the older vehicle and add in a pump and suitable lines. There is nothing wrong as long as you do a professional job.
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Old July 12th, 2014, 09:19 PM
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Quote:
Originally Posted by samer0214 View Post
If I understand you correctly, you are suggesting upgrading the 3.5L with the 3.9L heads, valve job, etc. Did I misunderstand?

What I'm suggesting is a rebuild of the 3.9L EFI for an eventual swap, ditching the 3.5L.


A little advice that will assist you in deciding how to proceed would be to do both a compression check on the 3.5 and also a vacuum check which will show what shape things are in. If compression is even and vacuum is constant you are good, if vacuum dances you potentially have one or more wiped lobes or a spark issue.

I'd buy the complete 3.9 with the harness and ecu for that price regardless.
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  #10  
Old July 12th, 2014, 09:24 PM
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Carb rebuild vs FI swap vs engine swap

Red90: Thank you for the reply, much appreciated.

Douglas: That's exactly the kind of advice I was looking for. Again thank you. I can do the work myself, not a problem, except for adjusting the carb (unless it doesn't need it out of the box?).

Let's see what happens with the purchase of the 3.9L.
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Old July 12th, 2014, 09:25 PM
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IMO the 4 bbl carb route is a lot of headache. You need to set it up to work and then cold or got or altitude or angles and it does not work properly.
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  #12  
Old July 12th, 2014, 09:30 PM
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Something to think about definitely, especially after my SU carbs locked up on me today (temps in the upper 80's here today). Another factor for me is that my camp grounds are at 5,000 ft in the Sequoia National Forest. Perhaps carbs are not the way after all?
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  #13  
Old July 12th, 2014, 09:48 PM
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I'm right in the process of doing this.. Customer wanted an RPI engine installed with fuel injection so it's now a worked 3.9 with upgraded chip... From the original 3.5 twin carb setup.. This also lets you use a decent a/c compressor and bracket on the right side of the engine and pits the alternator on the left.. It's not a big deal once you get over the mindset that it is... The whole fuel injection system only need like 5 wires to run and that's power.. Ground and switched ignition... You can also connect to the vss..(vehicle speed sensor) and a couple of wires need to be rewired to the gauges.... The harness on the fuel injection harness comes out on the left side of the engine as opposed to the right side on the carb one.. There is also a/c compressor input and output wires from the fuel injection ecu.... From memory it waits until the engine idle stabilizes before it switches the compressor on if I recall correctly...you will also need to connect up the oxygen sensors into your exhaust also..... You could either wire in the fault code box or have to read the codes with a scanner whenever the light comes on for a fault in the system..oh, and you have to take one wire to the dash lights for a engine fault light.. Quite simple really...lol... If you like I can show pics...I'm actually doing all of this today and tomorrow..)

------ Follow up post added July 12th, 2014 09:51 PM ------

I'm also getting ready to do the holley fuel injection system onto a 4 barrel edelbrock manifold.. That system looks very nice with multiple fine tuning adjustments.. ..should be very neat and tidy setup..
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  #14  
Old July 13th, 2014, 05:13 AM
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Shayne: That sounds very interesting and looks like what I'll do. My D110 is a RHD 1986 with carburators. I'd be very interested in pictures and any details you can provide. I'm sending you a PM with my email and contact info.

Thank you - Samer
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Old July 13th, 2014, 08:33 AM
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Got your PM.. I will post some pics up here just in case someone else wants to think about it... It really is the way to go... My buddy ed in Alaska also did this swap a while ago.. He would also have some great insight..he owns steadfast offroad and is a really nice and clues guy... He may have documented it a bit more than my winging it as I go kinda deal..lol..
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