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Thread: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

  1. #1
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    Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Getting this thread started since I'm almost finished with the conversion. Post any questions you may have about it here, I'm using this writeup as a reference as well as adding my own info where there seemed to be some ambiguous steps. The cool thing is that you can do this to pretty much every Jeep vehicle that has the 258 in it.

    Donor vehicle is a 1994 XJ, 160k miles


    Will post photos when I get a better internet connection.
    This is being performed on a 1989 Jeep YJ, 4.2L with a Weber 32/36 and TF999 3-speed with column shifter. System will be swapped out for complete multi-port fuel injection with computerized engine management and on board diagnostics from the 4.0 system.

    Here we gooo:
    Rebuilt head picked up from the guy who was parting out his '94 XJ which became the donor. Was gonna redo the top end but ended up selling it due to leaving to enlist in the Navy.

    I had taped up all the holes on the bottom to keep them clean while I did a mild port / polish job on the intake and exhausts.



    First thing is first, the water jackets need to be welded up. The 4.2 block follows the curves of the pistons, whereas the 4.0 is square and follows the flat edge of the head. If these holes aren't sealed there is nothing on the block to come into contact with the head in these regions, which leaves open gaps where coolant will just dump out onto the ground if you try to refill the antifreeze.


    Water jackets all sealed off about a half inch deep using leftover "ecofriendly" packing peanuts (basically just corn starch puffs like Cheetos but unflavored) - you can test if you have them by dipping them in water and they dissolve into sugary goop. Or you can eat them like I did. lol


    All sealed! The JB Weld is basically syrup when you're placing it in, and it wipes off cleanly with rubbing alcohol so you can make as much of a mess as you want (Like I did)
    Just make sure none is sticking over the head surface unless you plan on sanding/milling the head down.


    Cleaned up and ready to take to the shop
    Last edited by JD Night Fox; 05-28-2015 at 04:34 PM.

    bsns. Just got srs.

  2. #2
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Subscribed.
    Jeff

    Drink More Water

  3. #3
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    I just got done doing something similar, it's a fun project! Did you deck the block at all?
    I'ma cookin' somethin' up!

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L


    Here's my pile of parts for the build! I dedicated a little section of the garage for them


    And here are all the parts that I didn't bother messing with; Hopper's Automotive in Tempe did the work for me for a total of $979.95

    MSD electric fuel pump
    4.0 High Output head
    FelPro head gasket
    rebuilt / cleaned thermostat housing
    4.0 complete distributor
    Crower highroller cam
    Crower chromoly hydraulic lifters
    Crower high rev springs (already installed on the head by me)
    new manifold gasket
    Intake manifold
    Rugged Ridge 6-2-1 headers (does not clear the intake manifold on cylinder 6 - needed to be modified)
    Hesco harmonic balancer / CPS kit (let me tell you, this makes changing the CPS the eighth wonder of the world)




    ================================================

    Currently trying to figure out why I'm getting no spark. Who has a 94 XJ they want to use as a guinea pig? What should the coil plug on the wiring harness look like? I'm using a 12V plug from the original wiring harness but I'd like to use the MPI harness

    EDIT: Ran a test through the coil, it may be bad... 1.4ohm between +/- and 12.4kohm between + and output, anyone with a mid~90's 4.0 able to test theirs and compare?
    Last edited by JD Night Fox; 12-15-2015 at 08:21 PM.

    bsns. Just got srs.

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Are you using the stock YJ ignition system or are you trying to change it to something else?
    I'ma cookin' somethin' up!

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Quote Originally Posted by TanTJJim View Post
    Are you using the stock YJ ignition system or are you trying to change it to something else?
    Oh, forgot to include that. let me put that in the top post

    Quote Originally Posted by TanTJJim View Post
    I just got done doing something similar, it's a fun project! Did you deck the block at all?
    Block is untouched, I had the engine rebuilt 16k miles ago and I'm just looking at power difference between the two heads.



    ================================================


    My AAA roadside assistance delivered the finished product back to my house last week. Here we go, round two!



    What the finished product looks like under the hood, untouched



    Pile of all the old parts in the back for now, will sell them off later to try to recoup some funds


    Here's a day shot for better quality

    One thing I forgot to include originally was the quick disconnect fuel lines - the connectors can be bought on Amazon for $12, otherwise an auto supplier will quote you $170 for the inlet and outlet lines.




    Comparison of the old vs new manifold gaskets
    Last edited by JD Night Fox; 05-28-2015 at 04:48 PM.

    bsns. Just got srs.

  7. #7
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Gotcha, I originally thought you were keeping the carb. When I said I was doing something similar I lied, I did almost the exact same thing you're doing but I sourced the fuel injection parts from a '96 XJ which is very similar but has a couple minor differences. I actually just got it running last Saturday, if you ever have any questions or want to check it out let me know.

    As to your no spark problem, those resistance readings sound reasonable. Resistance between + and - sound a tad lower than expected but I'm not sure of the specs for that particular coil. Do you have the cam and crank sensors hooked up? And I know it sounds like a stupid question, but I assume you have the wiring from the XJ sorted out and hooked up?
    I'ma cookin' somethin' up!

  8. #8
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Double post.
    I'ma cookin' somethin' up!

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Yeah crank sensor is tripping the ASD relay when trying to start so I know that sensor is working. Cam sensor is plugged in, not sure how to test that one though, the voltage reading from coil output to ground is 0.03 which is kinda strange, but I wouldn't know for sure.


    =================================================


    View from opposite side, new distributor and wires already installed and ready to go!

    Now for the fun part, figuring out where all of this goes:


    Poking around at a good spot to put (most of) it




    Forgot to put the valve cover gasket on so getting that done before I proceed any further.


    Fuel pump blockoff plate w0w

    33 wows/ph


    Lining up the stock injectors, gonna run these before I put on the 784's since I've had a few issues with them in the past


    And here's a picture of a 784 injector with the USCAR to EV1 adapter - plugs in perfectly to the 4.0 harness!
    You can find info on this injector swap mod here and the guide to swap them out in here

    The adapters I bought from "OBD Innovations" on Bonanza here's a direct link because nobody wants to go searching around for them
    These ones work and are WAY cheaper than other websites. USPS also messed up my address and returned them to the seller because they couldn't find my PO box, and the seller even resent them a second time free of charge to my home address.
    Last edited by JD Night Fox; 05-28-2015 at 05:02 PM.

    bsns. Just got srs.

  10. #10
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    If you have a wiring diagram you should be able to find the signal wire from the cam sensor. Backprobe it with a multimeter while cranking the engine and it should switch from 0V to 5V. This might happen too fast for your meter and it might just read around 2.5V but that's normal operation as well, usually as long as it doesn't stay at 0V or 5V it's working.

    Your ignition coil with the engine cranking will have 12V on one side and the other side will switch from 12V to 0V. Again, this might happen faster than your meter can pick up so it will probably read somewhere in the middle. The coil is also powered by the ASD relay so when it isn't turned on you won't have power at the coil. IIRC, the ASD relay should turn on all the time when the key is on but I could be wrong on that.
    I'ma cookin' somethin' up!

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Quote Originally Posted by TanTJJim View Post
    If you have a wiring diagram you should be able to find the signal wire from the cam sensor. Backprobe it with a multimeter while cranking the engine and it should switch from 0V to 5V. This might happen too fast for your meter and it might just read around 2.5V but that's normal operation as well, usually as long as it doesn't stay at 0V or 5V it's working.

    Your ignition coil with the engine cranking will have 12V on one side and the other side will switch from 12V to 0V. Again, this might happen faster than your meter can pick up so it will probably read somewhere in the middle. The coil is also powered by the ASD relay so when it isn't turned on you won't have power at the coil. IIRC, the ASD relay should turn on all the time when the key is on but I could be wrong on that.
    The ASD activates from the crank sensor signal so it's off on ignition until cranking. I'll get some probes and test the two later today. The spark plugs smell like gasoline when I pulled them so I'm assuming the injectors are working at least, which means the cam sensor should be functioning.


    ================================================

    New CPS location - right next to the harmonic balancer! In this position the sensor plug is not long enough to reach the wiring harness. I added this extension:


    Using the CPS off of the old engine, I cut the wires right where they come out of the sensor and then spliced them onto the crank sensor connector piece from Hesco - was the exact length I needed to connect it to the wiring harness.

    Now for some fun wiring time, luckily I spent multiple hours with a probe trying to figure this out so you don't have to

    Here's the dark blue wire the mod talks about - this is the "hot on ignition" power source. The yellow wires on the stock carbureted YJ harness are also the "hot on ignition" sources that you can tap into. I used the manifold heater plug like the mod says, all I needed to do was get a few prong connectors from Lowe's and connect one to the wiring harness socket and the other to the manifold heater socket - no soldering or wire cutting of the two harnesses necessary! (for now)




    This is the underside of the fuel pump relay. The dark green with white stripe, shown at the bottom, is the pump output wire. This one you can also find on the end of the wiring harness, just like the ignition power line.

    The fuel pump relay and ASD relay are OFF on ignition. The CPS sends a signal to the computer when you start cranking and it energizes both of them. The fuel pump initially runs for about 1 second when you turn the key so it can prime the system. You can verify if the relay is working correctly when it does this. When you start cranking the engine, the fuel pump should start spinning again. Another verification that the relays are working as they should be.




    more wire testing pokepokepoke


    Here's the rest of the harness end, as well as all the wire colors you will need to know, especially if you plan on hooking up the "check engine light" kit (which I did)

    Black with pink stripe, as seen on the bottom right, is the PCM ground for the check engine light. The white with black stripe at the top is an "always on" power line for the instrument cluster on the inside of the cab. The check engine light connects into these two *the instructions on the Hesco kit are very vague*
    These DO work, as I have already verified by my engine already throwing codes at me without it even running yet
    Last edited by JD Night Fox; 05-28-2015 at 05:17 PM.

    bsns. Just got srs.

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Justin, are you still using the engine wiring harness from the 4.2?
    '93 YJ, 4.0, NV4500, Atlas, 35s
    '17 WK2, 5.7, ZF8HP70, NV245, 31s

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Quote Originally Posted by TreeKiller View Post
    Justin, are you still using the engine wiring harness from the 4.2?
    I have the complete 4.0 wiring harness hooked up to it, but I'm not sure which plug is the one for the coil input

    Engine computer is currently throwing code 12 (battery unplugged from computer during last 50 startups), 33 (no AC relay), 41(No alternator relay)

    unplugging the cam sensor also throws code 54 (no cam signal detected on crank)

    =========================================


    Got everything mounted



    Put the fuse box and computer both on the side with the battery, that way there's room for the airbox on the opposite side.


    Also found a great deal on those Iridium fusion spark plugs online, got 6 of them for $27 shipped
    Last edited by JD Night Fox; 05-28-2015 at 05:20 PM.

    bsns. Just got srs.

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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Just finished putting all the photos on. I'll make sure to add more as I see fit so I'll let everyone know.

    bsns. Just got srs.

  15. #15
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Cool, some vehicles will turn on the ASD relay with ignition on. Since yours will only turn it on when cranking then you'll only have power to the coil when cranking or running. The connector for the ignition coil should be unique to the coil too so it should be fairly easy to determine which one you're looking for. Also, it will come out of the harness in the same area that the cam sensor connector comes out of.

    Looks like fun so far!
    I'ma cookin' somethin' up!

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