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1,641 Posts
4 to 8 Swap Parts List
87-93 Mustang

V-8 Engine
Manual or Automatic Transmission
A Complete V-8 Exhaust System will be required. (Tailpipes are different for the LX and the GT).
Fuel Lines (from Fuel Filter to the Fuel Connection at the right Front Framerail). (The 4 Banger is on the left Framerail).
Brake Lines (the ones that run underneath the car on the right side) with Connector (above differential). The 4 Bangers are on the left (drivers) side.
2 Brake line Brackets. (These are found at the front brakes where the hard lines connect to the soft lines). (They are different for the two cars).
8.8 Complete Rear End with Sway Bar. (No need to change the upper or lower control arms as they are the same).
Drive Shaft ALL are interchangeable EXCEPT those from a 2.3 Automatic (throw those away). From the 2.3 with the 5 Speed can be used but have a "balancer" at the front yoke.
Front Brake Assemblies (Spindles, Dust Shields, Rotors and ALL hardware). NOTE: There is NO need to change the Lower Control Arms. They are identical for the 4 bangers and the V-8 Mustangs! (I don't give a damn what you have been told! I just did this swap on my 1992 4 Banger on June 1 2012) and had some 5.0 Lower Control Arms sitting in my garage too so I compared them, they are indeed identical! And by the way, the "K" Members are indentical as well! some say an INCH Difference, BS! To top all of that, the Ball Joints are the same too (I put new ones on and checked the part numbers for the 4 banger & the 5.0).
Front Coil Springs
Computer Wiring Harness (EFI Harness AKA Mass Air Harness). These are Year Specific! One from a 89 will also convert the 87-88 5.0 Speed Density to Mass Air. 1990 is a one year Specific. 91 through Mid 92 and then Mid 92 through 93 with the Fuel Relay under the MAM (Mass Air Meter).
(O2) Oxygen Sensor Wiring Harness (also Specific for the AOD or the T-5 5 Speed).
Additional Thermactor Switches (fit on the backside of the Right Shock Tower) with related Vacuum Lines. (not always required).
Headlight Wiring Harness (or Extend the Connections to the Alternator), (NOT Recommended).
Front Sway Bar (the 4 banger one is smaller)
Evaporator Coil for A/C (fits in front of radiator) (Larger Version is for a V-8)
Radiator. The 4 Banger one is the same but I recommend using a 3 row Radiator. Stock is only a 2 row in the 5.0 or 2.3.
Power Steering High pressure Line (or the Sensor can be removed from the 2.3 version and a Pipe Plug used).
Master Vacuum Manifold (located on firewall near brake booster).
Sticker showing serpentine belt routing
Coil Cover (or the appropriate Stickers).
A Vacuum Cannister must be added to the front right fender well area (between the fender & the plastic fender well). (Do this at the same time as when changing the Fuel & Brake Lines).
The Throttle Cable must be changed (the 2.3 is too short and of a different design).
The Cruise Control Cable that connects to the Throttle Body must be changed. (for the same reason as the throttle cable).
The Tachometer must be changed to that from a V-8 (all other gauges will be fine).

Fuel Tanks and Fuel Pumps are Identicle. (no changes needed).
Add Hangers for the Dual Exhaust on the Right side of the car. (They are already there for the Left Side on the 2.3 cars).
Add Quad Shock Brackets to the Rear Framerails.

Now if anyone needs more information on this subject or parts, e-mail me direct at; [email protected]
Don't waste my time asking me for Parts & Prices if you have no intent to buy, just ask the damn question and don't waste my time, PLEASE! I WILL ANSWER YOUR QUESTION. All I ask is that you don't waste my time.

Thank You All (and the Corral)

Recently added to OUR Corral:
1994 Mustang GT Convertible: Red Exterior Black/Gray Interior
1995 Mustang GT: Red Exterior Black Interior with Gray Seats

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1,641 Posts
Differences in EFI Harnesses for the 87-93 FOX

This ought to explain it !

87-89 (EXCLUDING California Mustangs, which in 1988, were MASS AIR), are Speed Density. To Convert these to Mass Air, you "have to have" an EFI Harness from a 1989 Mustang or one from a California 1988, ONLY! The only other option is to buy a Painless Wiring Harness. NOTE: The 1988 Calif. MAM "Plug" is OBLONG but can be converted to the OVAL Shape with the Newer (oval) Connector.

Now, from here on in, this information is for the purpose of Converting a 4 Banger Mustang (I DO NOT CARE If it is a COUPE, HATCHBACK or a CONVERTIBLE)! AND, I could CARE LESS "What You Have Been Told"! I've done HUNDREDS of these Conversions MYSELF and "I" have been doing so for the past 20 plus Years!

87-89 Use a 1989 EFI Harness. How do you tell? It will have the Round Gray and Round Black Connectors near the Brake Booster BUT, NO WHITE Connectors anywhere on this Harness (other than the big White 10 Pin Connector). It will also have the MAM (Mass Air Meter) Connector on it.
NOTE: If you find a Harness that does NOT have the MAM Connector on it, it is "most likely" a Speed Density Harness.

1990 is a "one year only" Harness. How do you tell? It will have the Round Gray and Round Black Connectors (just like the 87-89) near the Brake Booster, but WITH 2 Little White Connectors (for Air Bag Sensors) on the Harness near the MAM. Build Date of the car will be LATE 89 or within 1990.
NOTE: NO, you cannot use this harness on a 87-89!

91 through Mid 1992. How do you tell? It will have a Brown Connector near the Brake Booster. Due to Factory "Overlap", look also for the Fuel Pump Relay that will be a Black/Green "BOX" under the Drivers Seat. If it is not there, you have a Mid 92 through 93 Harness.

Mid 92 through all of 1993. How do you tell? Look for the Brown Connector near the Brake Booster but also Confirm that it Does NOT have the Black/Green "BOX" under the Drivers Seat. Also, Confirm that there ARE 2 Black "Boxes/Relays" by/near the MAM.

QUESTIONS? Feel free to e-mail me at [email protected] Don't bother trying to make it sound like you want to buy something. I don't care, tell me what you want to do, and or confirm.
YES, I have ALL of the Harnesses that you will need and/or Information! I just ask that you do not waste my time.

OK, I just flipped through a lot of the responses prior to this post and find that people are trying to Mix N Match Wiring Harnesses.
I'll make this really simple.
If you want to do a job and do it right, use the Right Harnesses! If you have a 1990, use 1990 Harnesses. If you have a 1993, use 1993 Harnesses.
When doing ANY Conversion, is is NOT Necessary to change the Dash Harness as long as you use the MATCHING Year Harness/es!
Got questions about this, and I know some of you do, feel free to e-mail me. [email protected] 23 + Years of experience doing STOCK Parts Conversions of all types.

Doing an AOD to T-5 Swap? There are a couple of Wiring changes that need to be made but you still DO NOT need to change the Dash Harness!

Doing A 4 TO 8 SWAP? See my 4 to 8 Swap Parts List 87-93 Mustang on page 7.


· Premium Member
1,641 Posts
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?


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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