4.0 head and EFI on a 4.2 block

Swaping 258 to 4.0, 4.0 parts to 258 etc!
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Wascally Wangler
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Re: 4.0 head and EFI on a 4.2 block

Post by Wascally Wangler »

New member, 1st time Jeep owner here. So it's an '87 with the "computer" controlled carb evidently. Drive it home from the purchase yesterday and everything seemed fine for. 39 yo vehicle. Tried to take it out for a DQ last night and it died at every traffic light. We have decided FI and 4.0 head the way to go but have to say I wouldn't have thought of it or had ANY confidence to try it without discovering this post string. Pete, pretty sure you're a genius... Anyway, I have a couple of opportunities to purchase basically "parts only" value keeps around here one being a '99 GC 4.0 auto. Since the aftermarket crank trigger seems to be the weak point and seemingly the guys @ the Jeep engineering dept seemed to have some other solution why wouldn't I be able to remove everything I need from the donor? Is the factory solution a bad one from the retrofit perspective?
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

RayW wrote:I finally got the CJ running. :rockout: 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
Glad to hear this Ray-- did you get the idle issue resolved? Sounds like a misbehaving IAC.

Please forgive the response time-- :doh: I check my email every three weeks or more, these days. Getting time to get on forums is even harder to find.
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

Wascally Wangler wrote:New member, 1st time Jeep owner here. So it's an '87 with the "computer" controlled carb evidently. Drive it home from the purchase yesterday and everything seemed fine for. 39 yo vehicle. Tried to take it out for a DQ last night and it died at every traffic light. We have decided FI and 4.0 head the way to go but have to say I wouldn't have thought of it or had ANY confidence to try it without discovering this post string. Pete, pretty sure you're a genius... Anyway, I have a couple of opportunities to purchase basically "parts only" value keeps around here one being a '99 GC 4.0 auto. Since the aftermarket crank trigger seems to be the weak point and seemingly the guys @ the Jeep engineering dept seemed to have some other solution why wouldn't I be able to remove everything I need from the donor? Is the factory solution a bad one from the retrofit perspective?

Welcome to Jeepdom!

Thank you. It is great to hear that you got some help/inspiration from this; that was the intention. :cheers:

you can certainly use everything from the donor. THe trick is using the 4.0 flywheel/flexplate AND correctly locating the Crank Position Sensor (CrkPS) on the YJ bellhousing. I am assuming your GC donor has an auto, correct? Have you looked into the compatibility of the GC flexplate with your YJ flexplate? (again, assuming the YJ has an auto) -- or are you thinking of putting the GC trans in your YJ?

(I may be repeating myself here) I am running a 4.0 flywheel and OEM crank sensor on my current version of my hybrid Jeep I-6. The Advance Adapters bellhousing came with the OEM CrkPS mount-- so it was a no-brainer.
zlieberman
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Re: 4.0 head and EFI on a 4.2 block

Post by zlieberman »

I've read through this thread a couple of times. Awesome thread by the way, it has helped in my swap.

I am in the middle of putting a 4.0 head on a 4.2 block and using all of the wiring harness and computer from a 99 cherokee. I can't get it started. I swapped in an aw4 years ago so I already have a 4.0 flywheel and I am trying to use a factory crank sensor. The engine will crank but will not start. I have adjusted the distributor cap and even turned it 180. Every once in a while it seems like it wants to fire up but won't.
Is it possible that the flywheel is indexed incorrectly causing the crank sensor to be off?
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

zlieberman wrote: May 8th, 2017, 7:09 pm I've read through this thread a couple of times. Awesome thread by the way, it has helped in my swap.

I am in the middle of putting a 4.0 head on a 4.2 block and using all of the wiring harness and computer from a 99 cherokee. I can't get it started. I swapped in an aw4 years ago so I already have a 4.0 flywheel and I am trying to use a factory crank sensor. The engine will crank but will not start. I have adjusted the distributor cap and even turned it 180. Every once in a while it seems like it wants to fire up but won't.
Is it possible that the flywheel is indexed incorrectly causing the crank sensor to be off?
Apologies for taking so long to respond to this. Somehow I got locked out and there was some glitch where I could reset my password. I'm in now. Did you get this figured out?
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Re: 4.0 head and EFI on a 4.2 block

Post by markncarj1 »

Not sure if anyone still checks this but I am having a hell of a time with this swap. Everything seems to work except when I run it for a min I reverse it to a steady throttle it starts misfiring. And exhause turns red as hell. It starts and idles perfect even at dead cold. Runs for 3 mins or so and dies. Turn it over again and fires right up and after a few mins at idle it dies again. I can hear the icv open to try to keep it going. After the 3rd start it will idle forever with no problems. Biggest problem is the first one. The misfire when heald at steady rpm. I did not cut the ear on the dizzy so it may be causing the problem. I can put a link up to a YouTube video if need be. This is a setup my son started and screwed it up so now I am back tracking his problems. Pls help
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Re: 4.0 head and EFI on a 4.2 block

Post by SkylinesSuck »

Retarded timing will cause high exhaust temps and could be related to the misfire as well.
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

I agree with the timing being retarted. It will run richer with retarted timing. This, combined with the extra fuel during cold-start/warm-up will cause the plugs to foul and misfire.

To confirm, the problem goes away once the engine is somewhat warmed up?

Yes, sounds like you need to properly index the dizzy - it is a crucial step that needs to be done correctly.

Have you checked the timing?
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Re: 4.0 head and EFI on a 4.2 block

Post by Urquiola »

Hi!: for inspection purposes, it would be good to me having the Jeep Cherokee 4.0 HO head and camshaft in the 4.2 Pacer engine, with the AMC double vase carburetor, but I ignore if this can be done while keeping the existing intake and exhaust Pacer manifold, necessary not to make the changes obvious to inspectors, as installing the injectors, intake and exhaust Jeep manifold would show. Any suggestion? Thanks. Salut +
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

Urquiola wrote: February 25th, 2019, 2:05 pm Hi!: for inspection purposes, it would be good to me having the Jeep Cherokee 4.0 HO head and camshaft in the 4.2 Pacer engine, with the AMC double vase carburetor, but I ignore if this can be done while keeping the existing intake and exhaust Pacer manifold, necessary not to make the changes obvious to inspectors, as installing the injectors, intake and exhaust Jeep manifold would show. Any suggestion? Thanks. Salut +
I do not think the stock 4.2 manifolds will fit on the 4.0 head. Please check and confirm this by searching in the rest of "swapology" section of this website. You can try filling in the 4.0 manifold injector holes in and smoothing them

Do you have a link to this racecar? It will be great to see, please
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Re: 4.0 head and EFI on a 4.2 block

Post by 86bansheej »

Is there any difference for doing this to a 4 speed manual cj? Do you need the computer out of a manual Cherokee or does it not matter at all?
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

You will be fine. That is the exact setup I ran- manual 4-speed with an auto trans PCM.

The only quirk will be when you hook up the speed sensor(VSS). It will hold a slightly higher idle until the vehicle comes to a complete stop
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Re: 4.0 head and EFI on a 4.2 block

Post by 86bansheej »

Did you use a manual jeep wiring harness or auto?
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Re: 4.0 head and EFI on a 4.2 block

Post by Jeep-Power »

Auto, as well. I got mine out of OBD1 Cheokees.
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Re: 4.0 head and EFI on a 4.2 block

Post by optmaxx »

I did this conversion over 10 years ago and I'm still using the harness on my stroker, but my memory is kind of fuzzy. I think you need to ground the NSS wire from the donor harness so that you don't get the high idle problem, I just can't remember exactly if it was the NSS wire that needs to be grounded. Cut off the dizzy ears in order to help you index it correctly, and I can't give advice on the crank sensor because I went with the Hesco relocation kit that relocates it to the harmonic damper; it's not cheap but it took a lot of the pain out.

You can't use a 4.2 intake manifold on a 4.0 head, but you can use a 4.0 intake manifold on a 4.2 head with some modifications. IIRC, the Hesco 4.0 intake had the power steering bracket ground off, and the dowel pin holes, as well as the bottom bolt holes were slightly modified so that it could fit the 4.2 head.

Make sure your vacuum lines are connected, and plug the ones that aren't being used, like any vacuum ports on your intake that aren't used need to be capped off. Make sure you firing order is correct by making sure your plug wires are going to the correct plug. Make sure you O2 sensor and cat are working properly, and make sure you exhaust is not being restricted by maybe a bad cat. If you haven't connected a MIL light yet, go ahead and wire one in to the donor harness so that you can see what's going on.
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