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4.0 in cj5 replacing 258

Swaping 258 to 4.0, 4.0 parts to 258 etc!
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tdagner
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Joined: April 24th, 2019, 10:49 am
Vehicle Year: 1980
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Vehicle Model: CJ5

4.0 in cj5 replacing 258

Post by tdagner » April 25th, 2019, 5:44 am

Hey Guys,

New to this forum. I am replacing a worn out 258 in my 1980 CJ5 with a 4.0 from a 1993 XJ. Ive got the jeep and about to pull the engine. IVe marked all wires with tape and labeled as I was disconnecting. Could really use some help on the wiring on this thing once i get to that point. Im keeping the Fuel injection.

One question that might be silly: will all the accessories from the front of my 258 bolt up to the 4.0? I want to stick with a mechanical fan and know that I have to switch to a wrangler water pump and fan to do that. I was thinking if my parts on my 4.2 will bolt right up then it would be cheaper and just as easy to do that.

Im hoping to have the engine out of the Xj tomorrow sometime and start on cleaning it up. Im planning on dropping it in and then cleaning up the wiring unless its better to clean up the wiring first? IM good with getting everything together, the wiring just freaks me out.

The donor engine had an auto trans so I am buying a flywheel. I will also need a pilot bushing, can someone point me to which one I need? my trans is the T176.

thanks

optmaxx
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Re: 4.0 in cj5 replacing 258

Post by optmaxx » April 26th, 2019, 4:36 pm

I'm using my accessories from my 4.2 on my stroker, like the pulleys, power steering pump, fan and fan clutch, and I believe the 4.2 water pump as well. I'm using the 4.2 alternator, but I modified it so that the 4.0 harness can control it otherwise you will always have the MIL light on if you connect a MIL to the 4.0 harness.

You can let the 4.2 harness control the 4.2 alternator if you don't plan to connect a MIL light to the 4.0 harness, but if you do connect a MIL to the donor harness, it will always stay on because the 4.0 PCM controls the 4.0 alternator. The way around that is to either modify the 4.2 alternator so that the 4.0 pcm controls it, or buy a PCM that had that malfunction code programmed out.

Modifying the 4.2 alternator is not hard at all, and all you need is the 4.2 alternator, a 4.0 alternator rebuild kit and I think a donor 4.0 alternator for extra parts. I followed a write up on an old Jeep forum that's not around anymore, and unfortunately I can't remember how it was done exactly, but it is the cheaper and most effective method to get rid of the code the 4.0 PCM will throw if it's not connected to to it's alternator.

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Re: 4.0 in cj5 replacing 258

Post by IH 392 » April 26th, 2019, 11:47 pm

You'll need to modify your bellhousing to accept the CPS, and I believe you'll need the one for a manual trans as well, the automatic ones are different, make sure the new flywheel is for the correct year engine your installing, and use the stater off of the 4.0 too.
You can get more power out of ANY engine!!!
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tdagner
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Re: 4.0 in cj5 replacing 258

Post by tdagner » April 29th, 2019, 7:06 am

Thanks, Im pretty sure the CPS is the same for both, looking at part numbers on rock auto there is no difference between manual and auto. I plan on modifying my bellhousing.

I got everything torn off the engine this weekend and about to order some new gaskets and paint to put it back together. I labeled every single wire as I unplugged it cause that is what frightens me most about this whole swap. I havent decided if I want to use the stuff from the front of the 4.0 or swap over the stuff from my 4.2. Its beginning to seem easier to just use the 4.0 accessories. If I do that though I need to figure out water pump and fan.

tdagner
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Joined: April 24th, 2019, 10:49 am
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Re: 4.0 in cj5 replacing 258

Post by tdagner » April 29th, 2019, 7:17 am

optmaxx wrote:
April 26th, 2019, 4:36 pm
I'm using my accessories from my 4.2 on my stroker, like the pulleys, power steering pump, fan and fan clutch, and I believe the 4.2 water pump as well. I'm using the 4.2 alternator, but I modified it so that the 4.0 harness can control it otherwise you will always have the MIL light on if you connect a MIL to the 4.0 harness.

You can let the 4.2 harness control the 4.2 alternator if you don't plan to connect a MIL light to the 4.0 harness, but if you do connect a MIL to the donor harness, it will always stay on because the 4.0 PCM controls the 4.0 alternator. The way around that is to either modify the 4.2 alternator so that the 4.0 pcm controls it, or buy a PCM that had that malfunction code programmed out.

Modifying the 4.2 alternator is not hard at all, and all you need is the 4.2 alternator, a 4.0 alternator rebuild kit and I think a donor 4.0 alternator for extra parts. I followed a write up on an old Jeep forum that's not around anymore, and unfortunately I can't remember how it was done exactly, but it is the cheaper and most effective method to get rid of the code the 4.0 PCM will throw if it's not connected to to it's alternator.
So with a stroker motor what engine parts are you using? would that be the 4.0 block, head and intake? Just trying to see if my 4.2 stuff will bolt up to a stock 4.0 motor. Im not very knowledgeable about the stroker build. Im looking to gain a little more power, stop leaking so much dang oil, and get decent fuel economy.

optmaxx
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Re: 4.0 in cj5 replacing 258

Post by optmaxx » April 29th, 2019, 3:39 pm

Here's my stroker build:

-1996 engine block .020+ bore
-KB 944 pistons
-4.0 connecting rods
-7120 Head
-1995 stock 4.0 camshaft
-4.2 crank turned .010
-24 lb injectors
-Ebay header for 4.0 engine
-4.0 intake
-Cherry Bomb muffler Part Number: 87522CB
-4.0 Pushrods
-4.0 lifters
-4.0 harness and sensors
-YJ gas tank but for fuel injected YJs.


Parts from 1990 4.2:

-All of the serpentine belt pulleys and brackets
-water pump
-Fan and fan clutch
-Power steering
-Modified 4.2 alternator to let 4.0 PCM control it
-Starter, but only because I went with the Hesco CPS relocation kit
-You can reuse your 4.2 rockers if you want, but I bought new ones
-Radiator
-Some of the 4.2 harness for some of the 4.2 components. Like the lights, NSS/Reverse lights, oil pressure switch and some of the components for the dashboard.
-Brake booster

Here's a Youtube video on the wiring. I used a harness from a 1995 XJ, and he's using a later one but he's correct on using 4 wires to get it running. The rest of the wires that you'd want to splice in from the 4.0 harness are for the RPM meter, MIL light and the NSS wire so that you can ground it.

https://youtu.be/PxiH3ZVreFU

I hope my post isn't too confusing since you're not doing a stroker build, but the stroker build is a 4.0 engine, just with 4.2 crank. So you would use your whole 4.0 engine as if you were just doing a regular engine swap, and then bolt up whatever 4.2 components you can like the one's I have listed. Your swap will be a little different than mine since you plan on modifying the bell housing, so I don't know what other mods or parts are needed for that.

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Re: 4.0 in cj5 replacing 258

Post by IH 392 » April 29th, 2019, 9:41 pm

tdagner wrote:
April 29th, 2019, 7:06 am
Thanks, Im pretty sure the CPS is the same for both, looking at part numbers on rock auto there is no difference between manual and auto. I plan on modifying my bellhousing.
They do seem to be, the Wranglers have different ones per manual vs auto.
You can get more power out of ANY engine!!!
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tdagner
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Joined: April 24th, 2019, 10:49 am
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Vehicle Model: CJ5

Re: 4.0 in cj5 replacing 258

Post by tdagner » May 2nd, 2019, 7:28 pm

optmaxx wrote:
April 26th, 2019, 4:36 pm
I'm using my accessories from my 4.2 on my stroker, like the pulleys, power steering pump, fan and fan clutch, and I believe the 4.2 water pump as well. I'm using the 4.2 alternator, but I modified it so that the 4.0 harness can control it otherwise you will always have the MIL light on if you connect a MIL to the 4.0 harness.

You can let the 4.2 harness control the 4.2 alternator if you don't plan to connect a MIL light to the 4.0 harness, but if you do connect a MIL to the donor harness, it will always stay on because the 4.0 PCM controls the 4.0 alternator. The way around that is to either modify the 4.2 alternator so that the 4.0 pcm controls it, or buy a PCM that had that malfunction code programmed out.

Modifying the 4.2 alternator is not hard at all, and all you need is the 4.2 alternator, a 4.0 alternator rebuild kit and I think a donor 4.0 alternator for extra parts. I followed a write up on an old Jeep forum that's not around anymore, and unfortunately I can't remember how it was done exactly, but it is the cheaper and most effective method to get rid of the code the 4.0 PCM will throw if it's not connected to to it's alternator.
Does anyone know how to mod the 4.2 alternator to work with the computer in the 4.0? Id really like to keep all the accessories off of the front of my 4.2 since that is the cheaper option by far.

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