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

  1. #16
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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
    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!
    Yeah that's the issue I'm having. I have yet to find a plug that matches the ignition coil socket.

    EDIT: I have a 6-prong socket that comes out near where the cam sensor plug is... Currently connected to nothing. I have no idea what it goes to, have nothing with 6 prongs to plug into

    If anyone would like to pull out random sockets from their 91-95 MPI harness and post a picture with a description of what it goes to, that would be nice. I want to add info for all the sockets to this since there are a lot of unused ones.
    Last edited by JD Night Fox; 05-28-2015 at 06:21 PM.

    bsns. Just got srs.

  2. #17
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    I almost forgot, those harnesses did have a larger connector that's part of an extension harness between the ignition coil and the main harness. IIRC it also goes to a couple other things like the AC compressor, alternator, and maybe a couple other things.

    If you take a look at the wires in some of the larger connectors that don't plug into anything, one will have a green wire with an orange stripe and a black wire with a grey stripe. Those are the 2 wires that will eventually go to the ignition coil. If you didn't get that extension harness don't worry, they're a dime a dozen at any junkyard. That might explain why you can't find a plug to go into the coil
    I'ma cookin' somethin' up!

  3. #18
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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
    I almost forgot, those harnesses did have a larger connector that's part of an extension harness between the ignition coil and the main harness. IIRC it also goes to a couple other things like the AC compressor, alternator, and maybe a couple other things.

    If you take a look at the wires in some of the larger connectors that don't plug into anything, one will have a green wire with an orange stripe and a black wire with a grey stripe. Those are the 2 wires that will eventually go to the ignition coil. If you didn't get that extension harness don't worry, they're a dime a dozen at any junkyard. That might explain why you can't find a plug to go into the coil


    Okay I've got a solid orange, solid black, black with red stripe, black with blue stripe, and white with orange stripe. The last one is an empty slot

    What's the connector called? I can probably order a new one off the internet

    bsns. Just got srs.

  4. #19
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    I don't know that it would have a "name". In Alldata it's connector C146 but I doubt that would help you find one online. It would seriously take all of 5 minutes to remove one in a junkyard.
    I'ma cookin' somethin' up!

  5. #20
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Quote Originally Posted by JD Night Fox View Post
    Okay I've got a solid orange, solid black, black with red stripe, black with blue stripe, and white with orange stripe. The last one is an empty slot

    What's the connector called? I can probably order a new one off the internet
    Quote Originally Posted by TanTJJim View Post
    I don't know that it would have a "name". In Alldata it's connector C146 but I doubt that would help you find one online. It would seriously take all of 5 minutes to remove one in a junkyard.
    Or call AMC 4x4 Salvage and see if they have one laying around....
    '93 YJ, 4.0, NV4500, Atlas, 35s
    '17 WK2, 5.7, ZF8HP70, NV245, 31s

  6. #21
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Back from my trip to the east coast!! It's time to get down and dirty once more.


    I took all of your advice and stopped at the Mesa Pick-A-Part, the first 1994 Cherokee I found had the exact harness piece I needed. Here it is:



    The 6-pin plug I thought was it actually goes to the transfer case. This one is an 8-pin further down on the harness.

    While I was there, I pulled the electronic throttle for the cruise control off because I'm going to do a retrofit cruise control mod later on (All the 4.0 harnesses have the cruise control plugs already, given you haven't chopped up the harness when you did the 4.0 head swap)

    Hooked up the pigtail and I'm getting the spark now, which is great, but now it sputters once every few cranks (like the timing is way off??? I don't know), and the computer is throwing code 14 that the MAP sensor voltage is too high/low after hooking the manifold vacuum up to it... I only recently found out that the fitting on the MAP is supposed to connect to the manifold via vacuum line

    now what
    Last edited by JD Night Fox; 07-01-2015 at 08:46 PM.

    bsns. Just got srs.

  7. #22
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Update #2

    bought a new MAP sensor to test it out, still not working and throwing code 14

    Probing the sensor wires, it looks like I'm getting no input voltage to the sensor when it should be 5v, the sensor output reads 4.09 volts
    Last edited by JD Night Fox; 07-02-2015 at 06:13 PM.

    bsns. Just got srs.

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

    Update #3 the input wire is magically getting 5v again after I unwrapped the wire tape around the socket

    The socket was smashed when transporting it to my house so I'm gonna replace it anyway, but it's still throwing code 14 even with the 5v input

    Edit: ran vacuum on the sensor with power on and the voltage dropped down with added suction, so it seems to be working, but still showing code 14
    edit#2: Might need to reset the computer, it probably has code 14 stored since it's something that would keep the lamp illuminated when in operation

    My next guess is that the timing is off, I'll need to find TDC on cylinder 1 and go from there
    Last edited by JD Night Fox; 07-03-2015 at 11:58 AM.

    bsns. Just got srs.

  9. #24
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L



    Update#4!

    Here is the engine bay fully assembled, aside from the PCV inlet and the air vent for the charcoal canister, which I need some rubber hose from the hardware store to hook up. The airbox isn't mounted to anything so I need to figure out how to get that held down. The YJ airbox mount was spot welded to the fender so I would have to saw one off and bolt it onto mine or something.

    The 5V issue with the sensor turned out to just be the wire not liking the direction it was bent, I replaced the plug with a new one and everything is working good with it now. Reset the computer and code 14 is no longer showing, it's still sputtering like it was before so next up is getting the timing aligned.


    Edit:

    Okay, with the dampener set to the 0 degree timing mark, the rotor is pointing toward the 5oclock position which is correct. The spark plugs fire twice each, I don't know if they're supposed to but yes it's getting spark. Still pops erratically every few cranks, at random, but won't turn over
    Last edited by JD Night Fox; 07-04-2015 at 12:23 PM.

    bsns. Just got srs.

  10. #25
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Cool, sounds like it's getting close! I ran into timing issues when i started mine as well, I'm sure you already know but the #1 cylinder needs to be at TDC on the compression stroke not the exhaust stroke, and then the distributor needs to be aligned. There is an alignment hole inside the distributor that you need to use to get the distributor where it needs to be. There should be 2 holes, one for a 2.5L and one for a 4.0L. It's really easy to figure out which one is which, as you said, with the rotor pointed at 5 o'clock you can see which hole lines up. If it doesn't line up with the hole in the base of the distributor you can grind down some of the tab on the distributor hold down to get it where it needs to be.
    I'ma cookin' somethin' up!

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



    Someone want to help me out here? Is this the correct angle for the cam sensor?

    bsns. Just got srs.

  12. #27
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L



    Here's the position at TDC (Well, -1 degree, close enough)

    bsns. Just got srs.

  13. #28
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Quote Originally Posted by JD Night Fox View Post


    Here's the position at TDC (Well, -1 degree, close enough)
    Here are the 2 things that need to line up, and in this picture they aren't lined up

    First thing, the hole that is at 12 o'clock is the hole you need to line up.

    Second, at the bottom of the distributor you can see a small raised part at around 1 o'clock, there should be a hole here, this is the second thing you need to line up.

    Line both of those up with the engine at TDC on the compression stroke and you should be good to go.
    I'ma cookin' somethin' up!

  14. #29
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Rockin! Got it figured out Tan. The distributor was off by 1 tooth, we're rolling hot!

    Now it doesn't want to idle and the RPM gauge isn't working. lol
    It runs okay if I give it a bit of throttle but not without that.

    Edit: Although the fact that I'm currently running just an open header may be why it doesn't want to idle
    Edit again: Idles fine now, I guess that was just the first few cranks while it was learning the correct mixture

    Now it won't shut off so I'll have to install the diode on the alternator as I was expecting. RPM gauge still shows 0.

    Code 14 is showing up again, getting 4.6v on the positive side

    What diode should I be getting for the alternator? I'm not sure if I can just use any one or if I need a high voltage one
    Last edited by JD Night Fox; 07-06-2015 at 04:39 PM.

    bsns. Just got srs.

  15. #30
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    Re: Operation 258 High-Output: 4.0 head swap conversion on the 4.2L

    Congrats! That has to be a load off finally getting it running!

    I don't have any suggestions for the diode or code 14 as I used a completely different alternator, but I have a thought on the tach. Are you trying to use the factory tach with the tach signal from the PCM? If so, it won't work as the PCM's tach driver isn't strong enough to drive the YJ's tach. What I've found that works well is tapping into the negative side of the ignition coil, you'll be able to get a tach signal from there no matter which one you want to use.
    I'ma cookin' somethin' up!

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