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Pedal Faster
2,658 Posts
Discussion Starter #1
Well I think I have a good deal on a low miles '98 Mark VIII whose power and drivetrain I can have. Last December I swapped in a '93 5.0, basically took every bit of wiring from under the dash to the front of the car, plugged it all in, made a couple of small modifications, and dropped the new motor in (I also converted to automatic temp control at the same time, I'm trying to find time for a writeup on that). That motor turned out to be kind of a turd, has a bunch of miles on it, runs well but is down on power (haven't had the heart to do a compression test). If someone could kind of go down the list and offer a little insight, that'd be cool (sorry if this has been discussed ad-nauseam, just point me to a thread if you don't want to write much).

Anyway, I've got this new DOHC 4.6 lined up and I have a few basic questions about swapping it in to my '90. Starting at the rear: I have an 8.8 trac-loc rear with 3.08s and discs that I pulled from the '93 (have the whole subframe, actually) and will be putting that in my car before I swap to the dual cam motor. I'll have access to the Mark VIII's rear, but it's safe to assume that is an open rear because of the traction control, right?

I'll be using the Mark VIII fuel tank and pump, as well as the exhaust. Any difference between Mark VIII tanks and others? I will be using the Mark tank instead of mine because I have the old style MN-12 tank where the exhaust hooks all the way over to the side of the car.

Transmission crossmember. Is there a difference between my AOD cross member and the 4R70W? If I have to use the Lincoln cross member, will it bolt up to the Tbird without modification?

Motor mounts: just use the Mark VIII mounts, yes?

A couple of wiring questions: I know that I will have to adapt some wiring, no problem there (will pick up a Mark VIII EVTM), but what about PATS? The Mark has its ignition switch and key, so that will still be fine, do I just stick the Mark VIII ignition switch up under the dash with the key in it, or ??? Will the Mark VIII ignition switch work in the Tbird column by any chance?

Also, I am going to use my '90 gauge cluster. I will wire that myself of course, but I would like to know if the tach out and speedo sensor out will work with my gauge cluster.

Also, since I won't have airbags, ABS, traction control (built in to the ABS controller?), no info center, any of that stuff, is that going to make the ECM unhappy, or is all of that stuff "output only"?

Any other thoughts? Sites I should look at? Threads I should look at? Discussion of the pitfalls of going to a mod motor in the pre-'94 Birds?

Thanks in advance, folks.

3,902 Posts
If I went with DOHC, I would probably use a SOHC 4.6 bird ECM and harness (can be easily adapted to DOHC engine, minus knock sensors but oh well). All I know for sure is that my 97 mark uses the SCIL module behind the glovebox to determine if the proper key is being used. Seems like it would be a pain to retain the PATS system and wire it into a car that didnt have it . Of course, I have never done a V8 swap into a 6 cyl car, much less a pre-94 one.
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