Which Mopar Jeep 4.2L EFI Conversion Kit?

[60Bubba]

My CJ-7 is now officially a frame off restoration.  The tub and parts go to the paint shop later this week or next.  Jeep Cosmos blue outside; Rhino liner inside and under the tub and probably the firewall and inner fenders.

 

Previously, Moses was helping figure out my Frankenengine.  It is a 4.0L from a 1995 Cherokee, but the old 4.2L had the MOPAR EFI kit on it.  I assume this is the EFI from the original upgrade, not from the junkyard 4.0L.  I couldn't determine if it was the 1995 and earlier or 1997 and later (returnless) kit.  I've included pictures of most of the fuel related stuff now that the tub is off. Maybe someone can help clear things up from these images.

 

Case

[Moses Ludel]

Case, this is definitely the later Mopar EFI conversion kit parts for a single rail system.  The giveaway is the pressure regulator (with filter built in), which is a modified 1997-up pressure regulator.  The factory '97-up system mounts the top portion of your pressure regulator atop the fuel tank module.  The modified version like yours takes the tank module regulator and adds a machined aluminum lower fuel chamber, making this a free standing regulator/filter outside the tank. 

 

You have the fuel pump that is common to both Mopar kits.  The earlier system uses a fuel filter and the remote fuel pump, your system does not need a replaceable fuel filter, as the filter is part of the 1997-up regulator.  (There's a sock at the fuel tank pickup as additional protection.)  The pressure on the earlier two-rail EFI is normally controlled at the fuel rail while yours is controlled by the modified '97-up type tank module regulator, which is now free of the tank.

 

Your rail should not have a factory return hose.  The hose I see going to a pipe is actually the return line from the regulator to the tank.  The regulator is supposed to mount closer to the fuel tank with a short return hose to the tank's gauge module return pipe.  It works the way your system is set up; however, your pump is pressing fuel a longer distance to the regulator and then a long way back to the fuel tank.  The remote fuel pump is designed to be mounted as close to the tank as safe and practical.  The 1997-up modified regulator/filter fits near the remote fuel pump on the engine side of the pump.  This regulator/filter should end up just a short distance from the pump and the fuel tank.  

 

Check to see whether the fuel rail has two parallel lines going to it.  If one is a return, that would be a two-rail system.  If there is no return line, that's the '97-up single rail.  The reason I bring this up is to eliminate the possibility that the 1995 two-rail intake was installed with the '95 4.0L engine, and the installer left the modified '97-up regulator in place.  This would by a hybrid with a fuel supply system like the later Mopar EFI conversion with a stock 1995 induction system.  

 

Would that work?  Well, yes it could.  The factory 1995 regulator and return line could be doubling up the fuel pressure regulation.  Pressure would be higher from the '97 up modified regulator. (1997-up operates at a higher pressure than the two-rail earlier system.)  The two-rail regulator, if the return line exists, is dropping the pressure lower than the modified '97-up regulator setting.  That could work.  Or, the two-rail 1995 EFI could simply have the return hose eliminated or blocked off, relying on the modified '97 up regulator to return excess fuel/pressure to the tank.  (Pressure is controlled by dumping the excess fuel volume back into the tank, which also helps prevent vapor lock by keeping fuel from stagnating in the lines.)  The higher pressure could make the engine run a bit richer.

 

What I'm suggesting is that the Jeep at one point had the later Mopar EFI single-rail induction system and fuel supply system.  It may still have all of that if the Mopar 4.2L EFI conversion intake was bolted to the 1995 4.0L head.  This will fit, I did it on my son-in-law's 4.0L engine swap into the '87 YJ Wrangler.  The entire later Mopar EFI kit was used with the 4.0L long engine—like your 1995 XJ Cherokee 4.0L swap engine.

 

The only point of interest at this stage is whether the installer swapped the 4.2L EFI conversion intake system onto the 1995 4.0L engine.  This is easy to determine by which intake manifold and fuel rail setup is in place.

 

Moses

[60Bubba]

I still only see one line going to the fuel rail area.  It definitely sounds like your suspicion from a month ago is correct, that this was the later MOPAR system.  I know it has the 7120 manifold, which was '91-'95, I believe.  Again, I have no way of knowing if this came with the EFI kit or was on the junkyard motor.  I don't suppose it matters much either way.

 

At this point, my only question is this: should I try to move the pressure regulator back closer to the external fuel pump?  I think I'm going to be bending some tubing anyway, so it's not out of the realm of possibility to do it.  Mounting the regulator might be a challenge, as it's currently on a welded mount, but I'm sure I could figure something out if it's worth the effort.  I'm planning to try to run rigid steel fuel line from the regulator to the fuel rail.  Right now, there is just a piece of hose with clamps running from the regulator up to the rail. It was literally just draped over the rear end of the engine near the bellhousing.  Seems like I can do better with materials and routing...

[Moses Ludel]

Sound like you do have the later Mopar EFI conversion setup in its entirety, 60Bubba!  I would mount the fuel pump close to the tank, it's a push type pump and likes to pick up from a short distance.  The pressure regulator/filter goes between the fuel pump and the engine.  Think of this in comparison to the factory 1997-up fuel pump module: pump in the tank, the regulator mounted atop the module (post-pump) then the single line going to the engine fuel rail.  Your tank return from the regulator can now be short and goes directly into the existing return pipe at the tank, as you share in your photos.

 

Here is a view of the factory pump module with regulator/filter at the top.  You can see the orientation of these parts, even though in your case they are outboard of the fuel tank.  This will make sense:

 

1997-up TJ Wrangler Fuel Pump and Sender Module.pdf

 

The "module" depicted has a filter at the bottom like your sock filter on the CJ pickup tube should have.  Inside the module, considered part of an assembly, is the fuel pump.  This is a actually a replacement item with an aftermarket Walbro (now TI Automotive) pump.  The unseen pump pushes fuel up to the "filter" at the top that looks like your remote regulator module.  In this case, though, your filter/regulator has a custom bottom chamber that permits the remote location outside the fuel tank.  The other component of the factory '97-up module is the fuel gauge sender, you see the float arm in this illustration.  Your CJ fuel gauge and float assembly are within the fuel tank with the two pipes coming out the top of that assembly or "module".  One pipe is the pickup pipe for fuel supply, the other pipe is the return line from original Jeep CJ 4.2L fuel filter near the carburetor.  Conveniently, the Mopar EFI conversion uses this return pipe for its filter/regulator fuel return to the tank.

 

An advantage of the shorter lines is quicker fuel return to the tank.  Even though the return line is unrestricted into the tank, the longer distance (current setup on your CJ) does create a load of sorts for the pump.  As you can see from the factory setup, the regulator is designed to simply spit the overage fuel right back into the fuel tank, with no return line of any kind.  With the Mopar kit's remote regulator/filter, I would try to shorter the distance to the tank and more closely emulate the factory method.

 

1981-86 Jeep CJ Fuel Tanks.pdf

 

Another concern is the pickup sock in the tank.  Above is the illustration of what that setup looks like.  (I included both the 15 and 20 gallon tank views.)  The sock is important in your case because it fits before the fuel pump and is the only protection for the electric fuel pump itself.  The filter/regulator is after the pump, so it only protects the injectors—not the pump itself.  I would want to make sure that the in-tank pickup tube filter "sock" is intact and clean, sealing well on the pickup pipe and serving the purpose of filtering fuel before the fuel pump.  If you decide to remove the tank/gauge assembly to inspect the pickup tube and filter/sock, look carefully within the tank for any signs of debris or corrosion.  If so, try to safely (no sparks, please!) clean up the tank while the gauge sender assembly is removed.  This opening is sizeable.

 

Moses