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Awesome thank you! I was worried I'd have to try to find another o2 harness! I was thinking I'd have to swap all the wiring from the 5.0 hatch to the notch, and the notch don't have A/C factory haha

So just plug the EEC 5.0 harness into the 4cyl's current wiring basically? (dash harness), and install the 5.0 cluster/EEC in the passenger side kick panel?
Late response but generically speaking yes.

5.0 swaps are pretty stupid easy on these cars. You can plug and play 99% of it, and for the other 1% most of anything being added/taken away has the correct mounting spots on the body already.

I suggest on the cluster to swap the tach/speedometer into the 4cyl cluster as a majority of the time the plastic boards are better on a 4cyl cluster. It's what I did with mine and it's turned out a lot better than a straight 5.0 cluster swap.
 

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Late response but generically speaking yes.

5.0 swaps are pretty stupid easy on these cars. You can plug and play 99% of it, and for the other 1% most of anything being added/taken away has the correct mounting spots on the body already.

I suggest on the cluster to swap the tach/speedometer into the 4cyl cluster as a majority of the time the plastic boards are better on a 4cyl cluster. It's what I did with mine and it's turned out a lot better than a straight 5.0 cluster swap.
Thanks man! I will do the tach/speedo swap for sure. Will be pretty easy since I plan to put white overlays on the faces anyway!

The only part of the wiring I'm worried about is the AOD ECU running a T5, and the o2 harness - I plan to clean and rewrap all the wiring anyway so I will verify it all then..
 

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about to start pulling the harness out of my donor car, im not sure of the year (no title)
it appears my 4 cylinder notch ( 90 ) has the grey and black plug behind the intake manifold that runs through the firewall.
the donor car has the same one, does this mean the harness going through the firewall wouldn't have to be replaced?
 

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Almost finished with my 4 t0 8 swap..... my car is 1989 coupe and my donor was an 89GT.....
Had a question. I have an 89 Almond notch auto 2.3. Thinking of finding an 89 that I can swap it all over. Figured that is the best way. Thinking a low mileage car may be best so under 100K if possible. Don't want to tear into the engine if I don't have to.

Matt
 

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MODERATOR'S NOTE: This is the merger of 4 different threads all dealing with 4-cyl to 8-cyl conversions. When threads are merged, all the posts are shuffled together in pure chronological order. So if it seems like some posts are redundant or irrelevant, well...then it'll look just like any other thread, won't it?

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You guys can post other things, but the only thing im going to post is the computer harness issue. IN the past weeks ive been doing a 4cyl to 5.0 conversion on my 92 4cyl convertible. As some of you know, 92-93 mustangs had the fuel relays mounted on the inner fender well's just below the mass air sensor. 87-90 mustangs had their fuel relay's mounted under the driver's seat as well as the 91's.

When converting a 92-93 4cyl to 5.0 you cannot use a mass air computer harness out of an 89-91 5.0. There are two suttle differences. The 89-91 harnesses do not have a fuel relay in it, and there are two large pin connections located next to the code test wires.

The 91-93 mustangs only have one large pin connectoin next to the brake booster, and the fuel relay is mounted on the harness next to the MAF sensor except for the 91 year. The fuel relay is still mounted under the seat..

When you try to use an 89-91 MAF computer harness on a 92-93 car, you run into two problems.

One, your body/dash harness only has 1 plug next to the brake booster to plug into the large pin connections of the computer harness, leaving one connector dead and unused, as it has nothing to plug into, and 2nd, there is no fuel relay next to the MAF.

why is this a problem? Simple. Since the 92-93 cars do not have a fuel relay under the seat, and since there is no relay on the 89-91 harness, when you try to use the harness on the car you get a car with no fuel relay, therefore the car will NEVER start, and NEVER run. The only way to make it work is to also to change the main body harness inside the car.

The 91-93 cars only have 1 large plug next to the code test plugs, therefore they need the correct MAF computer harness from 91-93 cars. If you are confused go outside and look at your car. Make note a 91 harness will not work with a 92-93 car, because the fuel relay is not located on the computer harness.

If its an 87-91, you will have 1 large relay mounted under the MAF
If its a 92-93, you will have 2 large relay's mounted under the MAF

If its an 87-90, you will have 2 large plugs next to the code plugs by the brake booster. One brown, one black.
If its an 91-93, You will have 1 large plug next to the code plugs by the brake booster. brown only.

So, to summarize.

if you are converting an 87-90 4cyl to a 5.0, you need a MAF harness out of an 89-90.

if you are converting a 92-93 4cyl to a 5.0, you need a MAF harness out of a 92-93.

if you are converting a 91 4cyl to a 5.0, you need a 91 harness as the 91 year is unique in its own.

When people are selling a computer harness and advertise that it is for 87-93 this is very misleading and false. Although you can MAKE it work by swapping out other harness's inside the car as well, it is not a simple plug and play as it would be for using the correct years.


This is all i am posting for now. Feel free to add to this thread with other information pertaining to this subject.

I had to edit this because I found out that 89-90 is the same, 91 is unique but similar to 92-93, and 92-93 is the same.
I really hope no one is using the information above to do a 4 to 8 cylinder conversion because although close, it is not accurate! [email protected]
 

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Hi, need some help please. In the final stages of doing my 4cyl to v8 swap and I can't find a clear answer. Car is a 90 2.3 and engine harness/o2 harness and ecu are from a 1990 as well. I tried to start the car and the fuel pump is not working. I keep reading the 4cyl have a ccrm? Do I have to splice in a fuel pump relay? Would it be same situation for AC? I can't seem to find a write up anywhere in the v8 swap forum on this issue.

Thank you
 

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1990 Ford Mustang LX 351M powered!! Project Cherry Bomb!!
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You've already got a fuel pump relay, it's under the driver's seat. You may need to try grounding it out to bypass it so the fuel pump will run in "key hot".. you'll find out the wiring on '90 models really don't match up to the diagrams a lot of the times...
 
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