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.
