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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, becuase 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.
 

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the engine bay wiring/computer install is the easiest part of a 4 cyl swap as long as you stick w/ the same year wiring harness that your car is. your info seems good but i do remember recently that a buddy couldnt get any wiring harness to work on his 93 conversion car except one specifically from a 93.
 

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actually, the early model 92 harness did not have the fuel pump relay, it was still under the drivers seat like the 87-91's. Later in the 92 model year is when Ford made the change. Anyone with a 92 has to see which version they have before getting the Main EEC harness for the conversion.

Also make sure to match your O2 sensor harness'. They are not all the same, and having the wrong one will sometimes fry the computer.
 

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Can use a 4cyl T5 if you change the pilot bearing to one out of a 1984 ranger with the diesel 4-spd.

Fuel lines run up driver side on a 4cyl, on an 8cyl they run up the passengers side. rear flex hose off the 7.5" rearend mounts on the passengers side, while the 8.8" rearends mounts on the drivers side. This makes for some creative brake line bending and braket modification.

4cyl cars have different front calipers, spindles, brake hoses, brake hose brakets, and a different master cylinder. Your going to want to upgrade all of these for optimum braking.
 

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I am doing a swap into an 87. I have a 100% complete 90 GT that has been hit in the front that Im using for the swap. I was told that I had to use a MAF harness and computer out of an 89 to make the dash work. Is this true?
 

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Discussion Starter #6
As far as I know so far, the 89-90 harness's are the same. Unless someone chimes in otherwise, you can always try it and find out. if you turn the key forward and your fuel pump doesnt prime, then yeha, you need a different harness.
 

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another thing for the conversions is that the headlight harness is different. the wires going to the alternator are shorter on 4 bangers. you can either extend it, or replace the headlight harness.
 

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from what I have learned (the hardway!) is there are 3 different styles.
I have seen so many different years Im not sure on exact years but
1) a 2 dash connector (gray and black)with NO air bags (89)
2) a single dash connector (red) WITH air bags (90- early 92)
3) 2 dash connectors (gray and black) WITH air bag (late 92-93)



make sure to grab the quad shock to frame mounts and pinion snubber..
 

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StaNgRuNer50 said:
I am doing a swap into an 87. I have a 100% complete 90 GT that has been hit in the front that Im using for the swap. I was told that I had to use a MAF harness and computer out of an 89 to make the dash work. Is this true?
you need MAIN EEC harness, Headlight harness, and O2 harness from an 89.
The 90 is different, as mentioned its an air bag car, and the green connector by the EEC is different. (well some of the pins are moved around)

also, The headlight harness from a 90 isn't compatiable with an 87. Compatiability for the headlight harness is 87-89 and 90-93.
 

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Discussion Starter #11
you can make the wrong headlight harness work if you still have the old 4cyl harness from the car. All you have to do is clip one of the pigtails off and put the one on from the 4cyl harness. You will see which one it is when you try to hook it up. both have the same colored wires, but they have a different stype of pigtail. jUst make sure you do it right and solder the connections and use shrink wrap.
 

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use the 88-89 mass air harness for your 87. just lengthen the alternator wires & use proper crimp connectors or solder the connections. this is what i did on my 4 cyl conversion car years ago & its still that way today. it took me maybe 15 minutes to install new wiring harness & computer!
 

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regarding the fuelpump relay fiasco, is there a way to add the relay without having to rip that entire body harness out? i'm stuck in the middle of a 88GT mass air car to 93 4-banger swap. i've got power to the dash and all, but no FP, obviously. i tried pulling the carpet up, saw that the relay was all part of that long-ass harness, and rolled the carpet back over it. is there any way to just add the relay in somewhere?
 

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Windchime88 said:
regarding the fuelpump relay fiasco, is there a way to add the relay without having to rip that entire body harness out? i'm stuck in the middle of a 88GT mass air car to 93 4-banger swap. i've got power to the dash and all, but no FP, obviously. i tried pulling the carpet up, saw that the relay was all part of that long-ass harness, and rolled the carpet back over it. is there any way to just add the relay in somewhere?

just get the correct harness and plug it in. Finished.
you will need one from a 93
 

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easier said than done. i need to get this thing running YESTERDAY, so trying to find a 93 harness is not in the works. is there a way to add a relay inline? does anyone know the colors for the wires that i can match them up?
 

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Windchime88 said:
easier said than done. i need to get this thing running YESTERDAY, so trying to find a 93 harness is not in the works. is there a way to add a relay inline? does anyone know the colors for the wires that i can match them up?
well, get some schematics, wire and a relay. start reading the schematics, and by the time you figure it out and actually do it you could have ordered the correct harness and installed it several times over, without the hassle and headache.


.... but yes, it can be added. but it isn't worth the trouble.
 

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nevermind. i just said 'f' it and yanked the gt harness. at least it runs now.

so, my addition to this thread:

-if switching years, make sure to keep the ENTIRE donor car until you've got the new one running. makes it easier to get everything together without having to hunt little things down.
-if doing a manual conversion, dont even waste time trying to take it out around the column. i wasted a good hour and a half just staring at the assembly trying to figure out how to snake it out. jank the column- it's only like 5 bolts/nuts and a couple connectors. with the column out, you can see ecactly how the thing comes out, and easier for fat-handed people such as myself to get the quadrant together.
-dont expect to have it done in a weekend. weekend projects always turn into weeklong projects.
-replace the throttle cable while the column is out. the 4 banger one will reach the throttlebody, but there's no way to hold it down. and its a PITA to replace with the upper on and the dash in.
 

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FOUR cylINDER to V8 swap

I have searched, and have not found a good write up on this.... if i am wrong, post a link.... I have a 90 gt that the motor is out of, and being rebuilt. I came into possesion of a 89 lx-4cl that is straight as an arrow, and i want to swap all the stuff from my gt into it. How involved is this? What all needs to be swapped, and what can stay? Any help would be great. I am starting this weekend.....:) :)
 

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do a search for posts by me about 5 months ago.. maybe later...

Anyway, with a parts car right there you could proly bang it out in a solid hard working weekend with a few friends....

List of Parts

Engine, Engine wiring harness/ecm, Headlight harness ( or extend 4cyl one so that the alternator. wires reach where the stock v8 alt. mounts), 8cyl tranni( can use 4 cyl T-5 with a different pilot bearing, but I wouldnt if you have a parts car and one available), Fuel lines, and brake lines run up opposite sides on 4cyl and 8cyl cars so your going to need those ( this includes the junction block where the rear flex line mounts on the body), Master Cylinder, font calipers/rotors/spindles/flex lines/brackets to mount flex lines to body, front struts (all brake parts besides lines are recommended... but you really should do it), new springs all around, 4cyl springs feel a little soft with a nice v8 under them, 8.8 rearend (not needed, but recommended for the power increase/ limited slip 2 wheel burnouts), new gauge cluster with v8 tach.. otherwise it reads double..... v8 bell housing, clutch cable(if going stick), throttle cable, heater hoses, radiator hoses, new fan.... thats all I can think of now... but there might be more, post questions if you need too.
 
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