4.0 head and EFI on a 4.2 block

[ranger3157]

Have not checked Swapology but I will, thanks for the help.

[87yj4play]

need help wiring my alternator on a 87 jeep yj with 4.0 head swap and harness off of a 91 yj jeep. which wire uses the diode? grn/blk share coil connection and the grn/org or could be grn/wht go into the harness. dose the diode go on the coil side of the wiring harness?
Brian

[Jeep-Power]

it goes on the line that supplies ignition power to the alternator.

A '87 alternator is not able to b controlled by the '91 PCM, as far as I know.

[gsrsilv]

I am in the process of doing this conversion. One question I have is which push rods do you use for the conversion. The 4.2L or the 4.0L? and is there any numbers on the computer that you can look at to tell if it is for an automatic trans or manual trans? This article is a great help thanks for posting it.

[Jeep-Power]

I am in the process of doing this conversion. One question I have is which push rods do you use for the conversion. The 4.2L or the 4.0L? and is there any numbers on the computer that you can look at to tell if it is for an automatic trans or manual trans? This article is a great help thanks for posting it.

I used the 4.2 rods. As far as I know they are interchangeable/ the same length. I remember comparing them side-by-side. I ended up using the 4.2 rods only because they were newer.

No idea on an easy way to identify the trans configuration of the PCM. IIRC the pinout will have certain cavities filled for an auto that are not filled on a manual (if you happen to have the PCM that came with your harness).

Otherwise, I don't think it is much of an issue-- (just hook up the VSS)-- the computer doesn't seem to care

Thanks-- I am glad you got something out of it!

[Jeep-Power]

do you have a breakdown on the wireharness what to keep what to ditch ??

76Jeep-
I am sorry I never replied to your post. Were you able to find something that helped? Is the Jeep running?

[Jeep-Power]

Hey Yall-

I am upgrading the head to a 0331 on my cj (need to run am MLS manifold gasket -- the fiber gasket does not like the turbo)

Here is a pic of the JB weld plugs after approx 100K miles. LOoks like they were weeping a little, but I have never seen so much as a drop on the ground underneath it.






I am going to go with 3/4" freeze plugs and silver solder this time-- a little more peace of mind.

[Richfan]

This is a great post. I am thinking about doing this head swap to my 90 YJ. I can get my hands on a 91 Cherokee complete car will this work? How is the new head 0331 swap going? You can't leave us hanging not knowing what's going on......lol.

[Jeep-Power]

This is a great post. I am thinking about doing this head swap to my 90 YJ. I can get my hands on a 91 Cherokee complete car will this work? How is the new head 0331 swap going? You can't leave us hanging not knowing what's going on......lol.

Thanks!

Yes, that '91 will work just fine!

Sorry-- I don't have a desk job anymore and rarely turn on the PC>


The head came out great-- here's the rest of the story~

This is a 'rebuilt' 0331 head off of Ebay. I contacted the seller before buying and they were happy to take the 7120 head as the core.

Using my jewelers drill and some carbide burrs, the head ports were cleaned up.
before & afters






valve collection-- the re-builders didn't lap the valves into the seats, so that got done as well



It quickly became clear that the freeze plugs were not going to work. The casting was too thing to support them adequately, and they would have protruded into the combustion chamber significantly and prevented the head gasket form sealing (BAD). I ended up using pipe plugs and milling them close to flat and then cleaning them up with a hand file.



It runs great- has no leaks, and the Multi Layer Steel (MLS) gasket works great with the turbo manifold-

More on that stuff in the link in my signature...

[lunzy]

Great post from a while back and I don't know if this will get to you but have to try! I have installed the Mopar MPI kit and have question about where to install the resistor to trick PCM about the alternator. I have installed the MPI kit on a 87 YJ 4.2L. Runs great. But check engine light is on giving me error codes 12, 33 and 41. I believe that the 12 and 33 are soft errors meaning they don't trigger the light but 41 is a Generator open circuit or short", something like that. Will that trick with the resistor fix this problem? Does the resistor go in the Field wire? If you could give me more information on where to install the resistor (1K - 10K ohm, 2 watt) I would certainly appreciate it. Need to get this fixed to pass California Smog Check!!

[jeepxj3]

Jeep-Power,
Your turbo looks sweet. How much power did it finally make on the dyno? What did you no for tuning? The fuel rail you made is very nice, I want one.

[Jeep-Power]

Great post from a while back and I don't know if this will get to you but have to try! I have installed the Mopar MPI kit and have question about where to install the resistor to trick PCM about the alternator. I have installed the MPI kit on a 87 YJ 4.2L. Runs great. But check engine light is on giving me error codes 12, 33 and 41. I believe that the 12 and 33 are soft errors meaning they don't trigger the light but 41 is a Generator open circuit or short", something like that. Will that trick with the resistor fix this problem? Does the resistor go in the Field wire? If you could give me more information on where to install the resistor (1K - 10K ohm, 2 watt) I would certainly appreciate it. Need to get this fixed to pass California Smog Check!!

I never did get to give that a try-- just ended up pulling the bulb on the CEL. ( I hooked it up to a lamp I had installed in the dash). I would try it on the field wire. Did someone state that resistor value? Do you know someone that will let you read the resistance of their OBD1 Jeep alternator?

[Jeep-Power]

Jeep-Power,
Your turbo looks sweet. How much power did it finally make on the dyno? What did you no for tuning? The fuel rail you made is very nice, I want one.

Thanks-- I am still loving and learning it.

at the wheels- 200 HP @ 3700, 300FtLbs @ 2700, stock cam, 6 PSI of boost, 100k+ on bottom end of engine. First dyno was on my friend's (IveyTune in NJ) Dynojet. Went to MoitionLabs in CHarlotte for load tuning - they have a Mustang - got the same numbers.

Thanks-- it is pretty.

[RayW]

I've just joined the group but I've read over some of the posts the past couple of months before joining. Peter has done a great job with the details he's provided throughout this message string, as well as a few other contributors. Although, a few posters seemed to drift off topic and it does lead to a bit of confusion.

I own an '84, CJ-8, which I had kept as original as possible for many years but the 258 c.i. just finally gave up the ghost and I gave in to the 4.0L head swap, after a small amount of work on the bottom end. I bought a '94 Grand Cherokee Laredo for the donor vehicle and the head was in pretty good shape but I took it to the cylinder head shop anyway, for new valve seals, seat grinding, decking and I did a little porting. The stock header on the donor was repaired at the bottom "Y' joint and didn't look to be a very good job of welding, so I bought a new header.

I'm about done with the swap with the exception of the installation of the PDC and wiring connections, fuel lines spliced in with fuel pump and filter and exhaust connection. I gather the wiring is everyone's biggest challenge, although Peter does make it sound quite simple. I think some of the discussion of the wire colors and pin locations does lead to some confusion for me. I've never claimed to be an auto-electrical wizard, anyway.

I have several questions related to the wiring and the answers may seem overly simple to some but bare with me.

1) There is a large plug that comes off the PDC which plugs in near the PCM. Many of the wires in that bundle aren't needed. Do you strip all those out of the bundle and cover the exposed ends? Most should have no power, anyway. Do you completely eliminate the plug and run the needed wires direct?

2) Peter mentioned only three wires need to be connected from the PDC but I see many other wires in his photo besides the three (DB to ignition, large R to battery + and BK/BR to engine block) he mentioned. I assume, these are the fuel pump and what else?

3) I did not locate a BK/BR wire in the PDC to ground. It may be a different color. Can anyone tell me exactly what should be grounded out of the PDC?

4) There are many unneeded wires in the original CJ harness, most are related to the carburetor and intake connections. What have most of you done with those wires? Did you cut them out? Are any required to be terminated in some way? Or did you just bundle them up and try to tuck them behind the engine?

Thanks and this group is very helpful to Jeep owner.

[RayW]

I finally got the CJ running. It took a lot of wire diagram tracing and a '94 XJ ECM to finally make it happen. The ZJ ECM just wouldn't let it run.

Now, it cranks right up but is idled too high. Any ideas how I can correct it?

Thanks