1990 Bronco II 2.9L to 4.0 Swap/Rebuild

[Moses1776]

Greetings, brand new to the site as far as posting a thread so I’m sorry if I’m doing this wrong.
I have a 1990 Bronco 2, came with a 2.9L and she’s a manual. I had been wanting to do a swap on it in the future but after a engine bay fire started and burnt some wires and hoses I sped up the process. I recently found a Ford 4.0L OHV on Marketplace and offered $200, as it was listed as sitting in a field for a few years under a barn side. The farmer said it came out of his 92 Ford Ranger. I went and picked it up and finally this week I started to take it apart. It took me about 6-7 hours and I finally got it stripped down. It had great compression to it but would get stuck right at the almost complete rotation mark. I stripped it down to find that Piston #3 was “stuck” and left a “shadow” in its place when pushed. Besides piston #3 they all were pretty great and I can’t find any other issues with this engine. It’s also important to say that I picked up the engine alone. No trans. And it’s missing some items, an ecu and it’s wiring, spark plug wires and it’s distributor, the intake and it’s assembly, and now pistons more than likely as it will need to be machined and probably bored for its own good after retrieving the stuck piston. I have many questions but until coming to the ranger station I only had answers from people who have never done this before. I’ve been told things like to bore it out. Carb it and get away from the ECU and EFI. But I want input from people who have been in my shoes before. I really appreciate your time taken to respond to me here and your generosity. This is my first engine rebuild and engine swap, so forgive my ignorance.
- Moses

 

[lil_Blue_Ford]

So, it sounds like the engine you have needs rebuilt at least. The 4.0 OHV is essentially a bored and stroked 2.9, so no real need to do anything beyond what’s required for a rebuild. That said, there are a few upgrades that can be done if you’re rebuilding. Get/have the internals balanced. Maybe a little hotter cam. Do the free-floating rocker arms (mentioned in the tech archives), flow port the heads and intakes. None of that is absolutely needed, but it will give you some gains.

You need a wiring harness and computer, preferably out of a 90-92 4.0 Ranger. It will largely be plug and play. Ideally you need a harness and computer out of a manual trans, but it will work with the auto, you’ll just get a CEL for no trans shifting and a higher idle.

 

[Moses1776]

So, it sounds like the engine you have needs rebuilt at least. The 4.0 OHV is essentially a bored and stroked 2.9, so no real need to do anything beyond what’s required for a rebuild. That said, there are a few upgrades that can be done if you’re rebuilding. Get/have the internals balanced. Maybe a little hotter cam. Do the free-floating rocker arms (mentioned in the tech archives), flow port the heads and intakes. None of that is absolutely needed, but it will give you some gains.

You need a wiring harness and computer, preferably out of a 90-92 4.0 Ranger. It will largely be plug and play. Ideally you need a harness and computer out of a manual trans, but it will work with the auto, you’ll just get a CEL for no trans shifting and a higher idle.

As I’ve said, your reply and input are much appreciated. So you think staying EFI is much better then the carb approach? Also, I was taking a bore approach to try and clean out that cylinder that piston #3 was stuck in. I can provide pictures if you’d like to take a look. I just figured it was needed after pulling a stuck piston head and finding a shadow marking left behind. I definitely don’t wanna rebuild it up for it to be “sticky” and cause issue. More power isn’t my biggest want in this. Reliability and durability are definitely more appealing to me than a Suped up piston launcher.

 

[lil_Blue_Ford]

As I’ve said, your reply and input are much appreciated. So you think staying EFI is much better then the carb approach? Also, I was taking a bore approach to try and clean out that cylinder that piston #3 was stuck in. I can provide pictures if you’d like to take a look. I just figured it was needed after pulling a stuck piston head and finding a shadow marking left behind. I definitely don’t wanna rebuild it up for it to be “sticky” and cause issue. More power isn’t my biggest want in this. Reliability and durability are definitely more appealing to me than a Suped up piston launcher.

Well, I don’t believe there were any carb intakes made for the 4.0, so you would be into a one-off custom deal. The EFI on these was pretty basic, same for the wiring and sensors. Since it can be a plug n play with the right parts, I don’t see any reason not to keep it. Plus, the fuel system was designed for EFI, you would need a lower pressure for carb, so something else to be changed.

I see what you’re getting at now, yeah, a hone job might be what you need if the rest is in good shape, no big lip at the top of the cylinders, no heavy scratches, etc.

The mods I’ve listed all help with reliability and performance. If you wanted a souped up piston launcher, then you just add a supercharger on top of all that.

 

[Moses1776]

Now my next question is when getting an ecu, will it matter if it came out of a ranger with a manual or electric 4x4? Is there any ways I can tell the difference between the two ecus if so

 

[alwaysFlOoReD]

Ecu has nothing to do with 4x4.

 

[lil_Blue_Ford]

Now my next question is when getting an ecu, will it matter if it came out of a ranger with a manual or electric 4x4? Is there any ways I can tell the difference between the two ecus if so

The 4x4 transfer case has nothing to do with the ECU, especially with these older ones. Automatic or manual transmission does make a difference. The electric T-case uses an entirely separate module for shifting, if your B2 already has an electric t-case, you don’t have to change anything. If it doesn’t then the easiest solution would be a manual t-case.

The automatic transmission ECU will work with a manual transmission, but it will have a persistent high idle and a constant complaint that it doesn’t “see” the transmission. The manual transmission ECU can’t be used with an automatic transmission because it doesn’t have the programming to control the shifting though. So it’s really best to match the ECU and transmission. My understanding is there is 4 basic ECUs for each motor and the choices are Federal emissions or California emissions and manual or auto transmission. Which emissions doesn’t really matter as much as which transmission.

 

[4x4prepper]

> Carb it and get away from the ECU and EFI.

Sounds like good advice since RBV parts are getting harder to find, especially quality ones. Your wiring harness is now "33" years old, it is not going to get more reliable with age, same as a 1992 harness.

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The 12a650 CPu was well made, BUT, it's components have a limited life span and that includes the capacitors, resistors, and the CPu itself. So, even if you stock pile 3 good ones, in 3-5 years they may all fail.

"The EEC-IV computer was built around an Intel-designed 8/16 bit processor called the 8061."

I program even today 6502 based computers in assembly language using emulators and if I wanted to, learning 8061 (8051?) to do a custom engine tune would not be that big of a deal. BUT, I would be hard pressed to print and design my own board with discrete components to match the existing wiring harness and 60 pins using a Raspberry PI.

Though things like this look awesome as a starting point:

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It means nothing if the thing you are plugging it into is DOA.

Go carb, you can always adapt a A4LD or better yet, put in a beefier transmission later.
$0.02