Modular Revolution Forums - 99-04 4v N/A into 96-98 Mustang Writeup...

Matt has posted his already, but I figured I'd post mine. I did mine in November 2004 after I blew my NPI engine. I have not edited the writeup at all, because I didn't want to lose what I was thinking at the time.

I'm getting a lot of questions regarding my 4v swap. While I don't mind the questions at all, the information I provide is a little redundant. Also, I'm getting older and as time goes by, the little details are getting harder to remember. I thought I'd start this thread to try to keep my memory in check.

My scenario is this:

I'm running an 03 Mach I 4v engine and 3650 trans in my 98 GT. The mechanical swap itself is no different than swapping engines with another 2v, so I won't cover the details. Any Haynes manual will cover the steps required. This discussion is meant only for the details required to make it run after you swap it in.

The following is a list of the intricacies one needs to be aware of when comparing my swap to your questions:
1. I'm using the 98 computer. I had all of the wiring and computer from the Mach, but I decided to stick with my computer for various reasons. One big reason is I wanted to stick with the return-style fuel system. The other major reason is the newer computer really didn't offer me a lot more for the work involved. The only thing I'd like that I can't have with my computer is a two-step. I'm using the SCT Pro Racer Package to flash the computer with the tune, so the other method for getting a two-step doesn't apply.

2. I kept the return style fuel system, because changing it over offered me nothing tangible that would outweigh the work involved.

3. I'm using the 03 4v injectors. I used these, because I sold the 42lb injectors with my supercharger. It was either the new style 24lb injectors, or my old 19lb injectors. The decision was easy.

4. I ended up using the 03 4v MAF with integrated IAT sensor.

5. I used my auto trans wiring harness to run the 5spd trans (only because I'm cheap).

6. I used the auto trans cross member, because the Mach's 5spd trans cross member wouldn't fit.

Now that the scenario is laid out, here are some of the things I needed to modify:
1. I had to splice the new injector wires into the old harness. This is fairly easy, because most of the injector wires are color coded the same between the two years. I just paid special attention to those that weren't the same.

2. I removed the knock sensors under the intake, because I couldn't use them with my computer, and they're a little sensitive anyway.

3. I had to extend the wiring harness to the two coolant temp sensors (both the coolant sensor and the temp gauge sensor). I welded a bung on the coolant down tube on the passenger side for the temp gauge sensor. O2 sensor bungs are the same thread style/count as the temp sensor, but it’s a little too thick. Right now my temp gauge is about 45 degrees too cool. If I had to do it again, I'd grind it down about 1/8 inch. I can predict where the temp is for now, but it's not quite right. That'll be fixed soon.

4. I had to change the oil pressure sending unit out for the old one (the connector is different between the years).

5. I had to ground the 3rd wire on the alternator. I grounded it to the alternator mounting bracket and it seems to be working well with no charging issues to date. I could have spliced in the Mach alternator harness, but I would have still had to ground that third wire somewhere.

6. I bought some 96-98 Cobra fuel rails to work with the return style fuel system. I bought mine from the resident parts god, Randy. I then had to bend the driver's side rail out to clear a bolt on the back of the intake. If you don't bend it out, the injectors won't line up right. They'll be pulled towards the rear of the car and will leak (just trust me on this one).

7. I also had to figure out a way to mount the fuel rails. I used some aluminum bent around the fuel rail and mounted in the stock location. Again, it seems to be working well.

8. I had to fabricate a mounting bracket for the passenger side coil pack. The driver's side mounts up with no problems using existing holes. I used some brackets from a hardware store and fabbed it up. Nothing major, but it looks stock.

9. I had to buy 96-98 Cobra plug wires. Again, I bought them from Randy. I had to get rid of the COP wires when I swapped out engine harnesses.

10. I then modified the plug covers to let the plug wires out. It isn't pretty, but function over form is what I was after.

11. I was fortunate enough to get the radiator hoses with the engine. At any rate, the hoses are completely different.

12. I had to modify the auto trans cross member to work with the 5 spd, because it was too wide to mount up to the trans. I cut a little notch out of it and it works marvelously.

13. I modified the auto trans harness to work with the 5spd. I cut the connector off of the trans range selector (little black box that goes on the detent lever). Out of that, I spliced two wires together. The two wires that need to be spliced together in order to start a 5spd with an auto trans harness are the white/pink and red/light blue wires of the old trans range sensor. I also spliced in the reverse light connector.

14. To get the speedometer right in a 96-98 car with a new VSS trans, one must use an extended range Speedcal. Once I installed that, the speedometer is fine.

15. I then flashed the computer with a tumble port tune provided by the good folks at SCT.

Edit: 16. I had a choice to make with the IAT sensor. I could either run it like the 98 with a separate sensor in the intake tube, or I could splice the wires into the Mach MAF connector. I chose to splice it into the Mach harness and use the integrated IAT. If I go to another supercharger, I'll change it back. The two wires to the IAT sensor get spliced into the two outside wires of the Mach MAF connector. It's that simple.

The bottom line is this swap is not too difficult. On a scale from 1-10, I'd give it about a 6 or so. The mechanical part is cake. If you've swapped one engine, you can do this. The most challenging part is making sure all of the wiring has been spliced correctly. If you can't read a wiring diagram, I'd recommend finding someone who can. I didn't have anything special. All I used was a Haynes manual for the diagrams. That being said, it is challenging to complete the swap and one can certainly get in over their heads quickly if they don't do some research before hand.