Gunn's 1995 3.8L V6 to 5.0 V8 engine swap DIY and lessons learned


4th Gear Poster
Sep 22, 2023
Vehicle Details
95 T-bird with 5.0and m5r2 swap for lemons
Country flag
Gunn's 3.8L to 5.0/302 Swap DIY (Notes)

Unlike my previous 3.8L single port to splitport 5.0 swap, this DIY will have far fewer pictures because a) I didn't take as many of them and b) they simply aren't necessary because you aren't fabricating any new parts (like that a new fuel rail and the whole throttle body mess with the Windstar). Instead, this swap was more straightforward mechanically but much less straightforward electrically (since I started with an 95 chassis vs. an 89-93). I've been told that this swap is much more plug and play with an 89-93 chassis but you go with what you have.

CURRENT STATUS 3/11/2014: Engine runs and idles just fine now. For a while, I had an issue where the engine would run just fine at speed (was able to drive it on a 200mi round trip) but had a hard time idling (when warm, it would try and die if allowed to drop below 1K RPM). I tried a bunch of stuff (see below for diagnostics) but ultimately, it looks like I was having a problem with my IACV and a bad coolant temp sensor (it fell apart when I tapped it). I replaced both and the engine runs just fine -- hot or cold -- now. My last remaining issue is tracking down a small coolant leak -- it's either at my thermostat housing (most likely) or at the lower intake (less likely but also a distinct possibility).

All in all, this conversion took me 225 hours (vs ~150 for BOTH splitport iterations -- Mustang and Windstar). I would attribute a good deal of this time to my desire to rebuild the bottom end of the 5.0 though (coupled with my inexperience in this kind of conversion).

This will be a LOT easier. The only reason I didn't take my own advice here is because I have $1500 into a professionally built roll cage in my 95 chassis.
- You will be buying a 5.0 tbird anyway to cost-effectively get the tbird-specific 5.0 parts (see below)
- Many of the 5.0 tbird parts are an upgrade for a V6 car (rear axles, TL unit) so if you will be swapping them from the V8 to the V6 car anyway, why not just leave them on the car?

RECOMMENDATION 2: Whether or not you keep your existing tbird or just trade it for the 91-93 chassis, consider rebuilding your your 5.0!
- The newest 5.0 tbird block is 22 years old now and I'm willing to be that 99% of them have at least 100K mi on them. While my sample set is fairly small (2 engines), from what I can see, the 5.0 engine is pretty worn after 2 decades and 100K mi.
- Even if you are keeping the 5.0 chassis (and therefore skipping all my electrical notes), take the effort to pull the engine and refresh it. At the very least, pull the pan and check the bearing clearances with plastigauge to confirm how worn out it is. You can then either buy a slightly newer explorer motor and swap the tbird specific parts over or rebuild your existing block.
- I was shocked about the affordability of the 5.0 bits: better cam? $185. New (uprated) valve springs? $150. Reground/reman crank w/ bearings? $150. Timing chain set? $30. This even extends to transmission parts: New Flywheel? $50. Clutch Kit? $70. Starter? $30. Seriously -- this stuff is stupid cheap so if you are taking this car apart, you might as well put it back together properly.

Anyway, if you insist on swapping over a 5.0 into your car, here's a documentation of what I learned. I couldn't have done this without Dan's help (SCTbird1994) -- esp the bottom end rebuilding -- or without the advice of MadmikeyL and Rayo.

Baseline (what I Started with)
  • 1995 Ford Thunderbird 3.8L N/A Chassis
  • M5R2 manual transmission w/ 89 SC flywheel (28oz imbalance) and 89SC clutch
  • Stock Hydraulic clutch line

Parts Considerations

V8 Decision - 4.6L or 5.0: I went 5.0 simply because I had two M5R2 manual transmissions already. The other options are:
- Go with a 4.6L and make a shifter relocation bracket for the matching T45 (or whatever it is) transmission. Swap?sort=3&page=1

- Go with a 4.6L from a 91-92 4.6L out of a Panther car (Town Car/Crown Vic/Mercury Grand Marquis). As I undestand it, they are called "b-stard" blocks because they have the AOD bellhousing pattern (to match an AOD or an M5R2) vs the more common "modular" bellhousing pattern. The catch is that they are fairly rare 23 years later. You are also opening yourself up to a whole different kettle of electrical wiring madness (adapting the towncar ECU and other bits to the tbird chassis).

Q: For an M5R2, which flywheel/starter to use?
Having committed to a 5.0/302 swap, this was the first decision I had to make. I already had 28oz imbalanced flywheel bits from an early SC to use with my V6. However, the 5.0HO as found in my 93 tbird donor cars (1 for racing, 1 for spare) have a 50oz imbalance. This means that in addition to acquiring a second flywheel, I would have to pay a machinist to rebalance BOTH flywheels to 50oz... a somewhat costly option which worried me a bit as this procedure has mixed reviews. Personally, I was skeptical myself of such a procedure.
- As an alternative, it was suggested to me that I might do better in endurance racing with an early style 28oz imbalance crank (1968-80). This would allow me to re-use my existing SC flywheel but since I had two engines, this would leave me with having to find another 28oz imbalance flywheel (early model SC) and pay for resurfacing of THAT disc as well.
- My solution? Raid the F150 parts bin. MadMikey told me that several years of F150s came with both my chosen engine (5.0 w/ a 50oz) and my chosen transmission (M5R2) so it was a simple matter of picking up a new flywheel, clutch, and starter for a "1995 Ford F150 5.0 V8 RWD".

There were only two downsides of going with an F150: different starters and slightly smaller (1/2") clutch discs. However, just taking a look at the F150 clutches and flywheels I purchased, they looked plenty beefy to me. While the starters are different from the truck to the cars, these parts were all cheap. Since SC flywheels are decently valuable, I was able to sell off my old flywheel without any fuss to recoup a good amount of my new transmission needs.

Parts Acquired from Donor Tbird
You will need the following items from your tbird 5.0 as they are tbird specific:
Engine Mounts
(can also be bought here but IMO it's not cost effective -- you want the Type 6 ones: Given their age, you may have to replace the rubber bits OR make your own (see below).

High Pressure Power Steering line
The high pressure PS line from the pump to the rack is different. Either (95+ or 93) low pressure line (from the rack back to the pump reservoir) will work but I kept my chassis's low pressure line since it included a provision for an external PS cooler (or in my case, I actually plumbed in a second one for a total of TWO PS coolers. Silly yes, but hey, it's endurance racing).

UPDATE (7/4/2014): After my last track day, I got sick and tired of having the PS low pressure line leak because the line as it mounts to the reservoir had cracked so much that there was a constant dribble. Since my car is stored for months at a time between races, having it puke out all its spendy Redline PS fluid was getting annoying. The solution was to buy a new PS reservoir with a nipple that exited towards the bottom, notch my accessory bracket as needed, and run a new PS line to the PS cooler. See this thread for part # and more details.

Oil Pan
Only the tbird specific one will fit without modification. I added a deeper oil pan but considering the extra work required, it might be more trouble than it's worth (certainly for a street vehicle).

Fuel Lines
Specifically, the section from the fuel filter forward to the engine. You need longer ones to replace the stock v6 ones. WARNING: Do NOT get cut happy here. I lost my backup set to my snip happy buddy and that's probably the only part I don't have a spare of now. I also got snip happy myself and had to rebuild the return line connector. The key is to disconnect all three fuel related lines (incoming, return, and vapor line) under the car behind the fuel filter at the removable connection. Luckily, I snipped the return line so the pressure is low enough that I don't mind replacing it with hose (my ~$20 Dorman fuel line repair piece had a connector mis-match with my chassis and therefore leaked a bit under pressure. Total waste of money).

Fuel Pump
If your chassis was a V6 N/A, you will need to replace the original 60lph fuel pump with the 88lph one from the 5.0 car. Or, you can just upgrade it.

5.0 Bell Housing Bolts
I noticed that I needed to use the bellhousing bolts from the 5.0 vs. the ones I used with my 3.8L N/A. I suspect it's because the bolts on the 5.0 were SAE (7/16-14 x 2" to be exact) while the ones I used on my 3.8L N/A were metric. Take them off the donor car or if those look like crap, just buy new grade 8 hardware at your local HW store.

The main computer for the 5.0. It was supposed to work with an AOD so it doesn't mess with the transmission at all (perfect for my M5R2)

Passenger side engine bay harness
This is the harness that goes through the firewall and terminates at the ECU plug. Since the 95 car had a provision for the CCRM (the module that contains the fuel relay and the main relay), I went with the 93 harness.

Rear 5.0 Axles
They are thicker than the ones that came with my 95 tbird V6. I pulled them with the spindles attached so replacement was a simple affair.

Throttle cable
It's different

Rear differential
Most 5.0s came with a traction lok unit which may be preferred if you have an open diff.
TIP: Rebuild it.

93 ignition control module
Its mounted between the airbox and the passenger side headlamp. You are looking for a small box with heat sink fins on it.

O2 Sensor extension harness
There is an 1-2' long extension cable that connects the passenger side O2 sensor to the passenger side engine bay harness. Don't forget to grab it or you will need to cut into your engine bay harness to make this sensor work.

93 tbird MAF, intake tube, and airbox.
While a 95 3.8L N/A MAF is larger, you will need a tune to make it work properly. If you (like me) are going to be stock for the initial setup, stick with the stock 93 MAF.

Optional: Radiator
Either the 91-93 radiator or the 95 radiator will mechanically fit the car so I just pressure tested all of mine and picked the best one (again, I'm trying to be frugal here for Lemons -- not all aluminum fancy pants stuff for me. A 91-93 radiator can be adapted to fit both the mount points (which are slightly different up top) and the radiator fan with some easily fabricated brackets.

Optional: electrical wiring
I harvested and sorted a good deal of the electrical wiring from my donor car -- especially the long runs that went from the dash area towards the rear of the car. This proved invaluable when I needed to make additional circuits.

Optional: battery cable
It's not very long but if your battery cables are in decent shape in the donor car, cut them out and use them for the additional grounds I cited below.

Recommended: exhaust
Technically, the 5.0 exhaust positioning (where the exhaust manifolds sit) should be compatible with the 3.8L exhaust so you should take a look at both systems and pick which one looks best.
If you want to modify the exhaust, I HIGHLY recommend contacting Mandrel Exhaust Systems. While welding will be required, MES will sell you prebent pieces cheaper than what the bends would cost you from Summit.
Here's what I built (video clips in the second thread)

Recommended: Fuel Pump Access Panel
Cut a panel from the metal floor from 93 tbird just above the fuel pump to make an access flap (see below).

Recommended: grab the Fuel Relay and its base from the trunk
You can use it for an electrical fan OR you can use it for your fuel pump (see below)

Optional: Suspension
The suspension on a 5.0 tbird IS stiffer than the ones found on a 3.8L N/A so if you haven't upgraded your 3.8L's suspension yet, you might want to look and see what your donor car came with.

Engine Internals / Upgrades To Consider / Prep Work

While it's less likely that you will need to get them ground flat like aluminum heads, your valve seats are probably pretty worn after 100K mi. A leaky valve seat was the likely cause of low compression in one cylinder on my "race" engine.

OPTIONAL: Head Upgrades
There are two options for more power on a budget
- port the e7 heads. Note: Porting Iron is a LOT more time consuming than aluminum.
- go with GT40 "3 bar" heads. Seeing what they go for on CL (~$300+) and considering how much they weigh, the only cost effective way to acquire them is to pull them yourself from a 96-early 97 Ford Explorer. You can still find them in junkyards (even after cash for clunkers killed off a bunch of them) and they seem to keep their value in case you decide to go with spendy aluminum heads in the future.
- go with GT40P heads from a 97+ Explorer: the change in how the spark plugs go into the heads will force you to add spacers (i.e.: cut off the flanges from some other exhaust manifolds) AND redo your exhaust from the manifolds on as they will be positioned farther away form the engine. Unless you are getting the GT40P heads as part of a fresher, lower mileage Explorer engine you are planning to drop in after swapping the oil pan, I'd skip it.
- If you are going to do any form of endurance racing with your 5.0, you really need to consider upgrading your valves to SS valves. I know it sucks to spend $400 on heads worth at best $300 (for GT40) or $40 (for stock E7 heads) but if you don't want valve leaks after your each and every race, you'll need them. $400 = $200 for Ferrea 5000 SS valves and $200 for labor.

Valve Springs
- Any engine you are rebuilding will have old springs. If you are already taking apart the heads to redo the valve seats, you might as well add newer springs.

- You can re-use the stock ones but if you do, you should recondition them. At the very least, buy the rebuild kits for a dollar or two each to replace the pintle caps and seats.
- Or, for a few bucks more, you can have them flow/spray pattern tested, reconditioned, and re-tested. I found Mr. Injector to be fast, affordable, and offered timely service.
- OPTION: upgraded injectors. You can also upgrade the injectors at this time because the stock injectors are close to their operational limit. However, you will need to tune the ECU if you go this route.

- All 91-93 5.0s use roller cams so this part is less likely to be worn even after 100K+ mi. Mine showed a little wear but nothing that can't be tolerated.
- Since the engine is apart though, you might want to consider a hotter cam. An e303 cam won't require a tune BUT will require newer springs to avoid valve float.
- Conversely, if you are adding new springs and the block is apart, you might as well add a new cam. Don't forget new cam bearings.

Timing Gear & Chain Set
They are cheap so if you are taking apart your engine, buy a new set.

Water Pump
This would seem obvious to replace given their cost.

RECOMMENDATION: Simplify the Engine
Remove the excess components. For my application (road racing), I didn't need a bunch of stuff so there wasn't a compelling need to figure out how to make it work.
- I don't have a heater core and furthermore, with the extra deep oil pan (see below), the 180 degree loop I was using to bypass the heater core was hitting the firewall upon installation. My solution was to cut the crossover pipe and then install it with a small stub pointing forwards (instead of backwards). This way, the fixture attached to lower intake manifold has only one provision for a temp sensor and then goes straight to the hose from the water pump.
- EGR: removed and a simulator plugged into the harness
- Smog Pump: removed. You will also need to weld a cap for the exhaust manifold.
- A/C compressor: ha! removed.
- Mechanical fan: this thing terrified me. I had no interest in getting my fingers near it. I also had to cut it off to get the WP off because it was so corroded on. Luckily, my 95 tbird has an electrical fan so all I needed to do was wire a switch and power relay for it.
- Simplify the vacuum connectors. You really only need 2 vacuum lines: one small one for the fuel pressure regulator and a larger one for the brake booster. I also hooked up the PCV valve from the lower intake manifold to the upper intake because that was easier than capping it and I ran another line from the upper intake to the nipple on the valve cover. All the other lines were capped.

NOTE: removal of both the smog pump and A/C compressor required a new routing of the belt. The instructions I found online for 5.0s was correct but the length needed was wrong. You need one that is 84.5" long

OPTIONAL: Manifolds/Header Upgrades
- Stock ones look tiny but anything better will either cost $$ or require the steering shaft to be relocated

OPTIONAL: Deeper Oil Pan
Oh man, I really made my life harder with this one. You can't really go wider b/c of the exhaust on the driver's side and the starter on the passenger so my solution was to go deeper -- 7qts to be exact over the stock 5qts. While you can fab this up yourself (provided you clean your old oilpan well so it doesn't catch on fire, you will also need a deeper oil pump pickup (relatively cheap from Summit Racing) This necessitated in notching the sub-frame and then for added peace of mind, I welded additional supports around it. This wasn't too bad b/c I already had a subframe out of the car I could notch and then test fit. Once I had the width down, I went and did it on the one still on the car. While this would have OK, the real problem here lay when I finally tried to fit the stupid engine into the car with the transmission. Even if I had unbolted the M5R2, there simply wasn't enough room to manuever the engine into position WITHOUT DROPPING THE SUBFRAME. The engine kept hitting the TOP of the transmission tunnel before the bottom end of the extra deep pan would clear the rear hump. Please note that this was after I raised the engine approx 0.5" (3 hockey pucks instead of two -- see below) over stock. To finally fit the engine, I raised the car, unbolted the rear 3 bolts on each side of the subframe, unbolted the struts from the car, and then loosened the front subframe bolts so the subframe would sag down and give me enough clearance. It was a total PITA.
Bottom Line: for a road car, I wouldn't bother with a bigger oil pan. For an endurance racing car, I probably would skip this upgrade had I known the trouble it would cause as well and figure out a way to hide an accusump (another reservoir which can supply addt'l oil on demand) in my budget (esp if I wanted to have the option of speedily swapping engines.)

Summary of Other Parts I Acquired based on my Decision Points Outlined Above
- 1995 F150 5.0 starter
- 1995 F150 5.0 clutch
- 1995 F150 5.0 flywheel
- New valve springs
- New camshaft & bearings (if desired)
- Reman/reground crank (if your existing crank is worn, a reman crank may be cheaper than getting your own reground. I bought a few from Autozone with free sihpping and just picked the best one -- aka the one with the smallest oversize bearings)
- O-ring for the PS pump (larger ring from kit, Dorman #82540)
- 1995 Ford shop manual & EVTM -- I couldn't have finished this project without these manuals
- 1993 Ford shop manual & EVTM -- you can buy both books for $10-15 on eBay
- Hockey Pucks & Grade-8 hardware (see below) for Engine Mounts: 1/2"-13 bolts, nuts, and lock washers. 3.5" long for 2 pucks, 4.5" long for 3 pucks
- Clutch line from hydraulic shop
- Shorter accessory belt: 84.5" (#845K6)
- Gasket kit
- Optional: thermostat housing (these are aluminum and mine actually broke when I unbolted it)
- Optional: New rear disc rotors & pads
- Optional: additional 00, 0, or 2 gauge battery cable for beefy grounds/power cables. You can buy battery cable lugs that crimp on from your local auto parts shop
Now that all the parts decisions were made, here's the summary of what you need to do assuming you have an 5.0 engine ready to install and an empty engine bay in your chosen chassis.

* As stated above, take apart your 5.0 engine. You might as well as you will be pulling it out anyway and parts are stupid cheap.

* Once you have the engine rebuilt, mate the engine to the transmission w/ the flywheel & clutch. I noticed that I had to re-use the 5.0 bellhousing to block bolts.

OPTIONAL: I have no idea why the disconnect for the hydraulic clutch line is INSIDE the bellhousing of the stupid transmission. While you have the line disconnected, take it to a hydraulic shop and have them make one in braided stainless steel for you with a disconnect in the middle of the line. While you are at it, you might as well make it slightly longer for ease of installation (I think mine is 3' long). These lines cost me $50 to have made (and $25 for a second disconnect-to-clutch segment for my 2nd engine).

* Install the starters.
NOTE: I'd like to point out two problems here:
1) First, my chosen starts had problems seating flush with the scatter shield. Now, I don't know if I used the 3.8L scattershield or the one that came with the 5.0. All I know is that since I found this issue AFTER I had mated the engines together (one was already in the car), I decided to use an angle grinder and grind away at the lip of the starter to make it so it could sit flush. Had I found the issue before the engine and transmission were together, I would have just made the hole in the scattershield slightly larger with a dremel (the positioning of the starter is handled by its two mount points -- not the scattershield).
2) The second issue I encountered I found much later: make sure the starter is properly grounded. I encountered some problems with the starter not being able to sink enough current through the ground wires and the solution was to run a dedicated 2ga ground from the battery straight to one of the starter's mount bolts. Problem solved.

OPTIONAL: consider making your own engine mounts and install them on your engine. I don't know about you but I had some serious objections to engine mounts at $30/side. Instead, I had a friend give me some of his old hockey pucks. I bought some fender washers, some locking washers, and most importantly, Grade 8 1/2"-13 bolts and matching nuts. If you want your engine to sit slightly lower than stock, go with 3.5" bolts and use 2 hockey pucks per side. If you want it to sit slightly higher than stock (ex: to help with the oil pan clearance b/c you don't want it to stick out below the subframe, use 4.5" long bolts and 3 hockey pucks/side. Drill a hole down the center of the pucks, add a fender washer to distribute flexing force, and bolt everything together. Quick and easy super stuff pucks. Now I understand that some folks have torn up hockey pucks in circle track racing and have gone to solid pipe/based mounts instead but I suspect the lateral motion is much more severe in circle track racing than in road racing.

* Clean the subframe area. You might as well get all the grime off as there won't be a better time to clean it. This will also allow you to more easily detect leaks. Notch the subframe and weld supports if you plan on using a deeper pan.

* Install the 5.0 fuel lines from just before the fuel filter

* Pull the exhaust. I found it easier to cut the hangers and re-weld them on but that requires a welder.

OPTIONAL: Your exhaust manifold studs are probably quite crusty; mine were so bad that I couldn't really tell what nuts i needed. The solution is to use a tap & die set w/ cutting oil to clean up the M10x1.5 threads.

* Drop the fuel tank and replace the fuel pump. As stated above, you'll need a bigger one. Go with the OE one from the 5.0 or just replace it with an upgraded one.

OPTIONAL: it's always a pain to replace the fuel pump so I fabricated up an access panel using a flap I cut off from the donor car.

* Replace the rear axles (recommended) and diff (if desired).

OPTIONAL: take a look at your rear brakes. If you haven't done anything with them for a while, now's a good time to replace the pads/rotors

* Replace the high pressure power steering line. I needed a new teflon gasket ring. Boil the ring and slip it on. You will want to do this BEFORE putting the engine in.

* Install the engine, transmission, and driveshaft.

* Connect the power steering lines

* If you left off the upper intake manifold to make installation easier, now's a good time to put it on.

* Re-attach your exhaust.

What you should have left is an engine that is mechanically in place but isn't hooked up electrically. Now, let's tackle the electrical items.


About the Electrical Harnesses:

- I kept the 95 chassis's driver side engine bay harness intact (the one that goes to the headlights and the ABS underneath the driver's side fender and terminates in a big round connector at the firewall) and the dash harness intact.
- I kept the driver's side engine bay harness because ABS on the 95 car is a standalone system (no involvement with the ECU) and could therefore be maintained even with the V8 swap.
- I kept the 95 chassis's dash harness because it was functionally identical to 93's harness. Had I opted for one of the donor car's digital gauge cluster though, I would have needed to modify/replace the dash harness. However, this was worth more to me as money than for the "oooh, digital dash" effects.

* Connect the two grounds that came with the engine: one should be on the passenger side and goes to one of the timing indicator mount points and the other goes from the driver's side to near the oil pressure sender.

PROBLEM: IF YOU STARTED WITH A V6, YOU'LL NEED MORE GROUNDS! After we figured out all the electrical communications connections required, we experienced all sorts of electrical gremlins. The starter would have a hard time turning over the engine (sometimes it would rotate a few revolutions and other times it wouldn't move more than 1/4" despite having the plugs out, oil primed everywhere inside the engine, and a fresh battery. The reason was because my starter wasn't grounded enough to sink all the current it needed (a V8, especially a fresh one, draws far more power than the V6 needed). The actual fix was to run a second 2ga cable from the battery to the body and a dedicated 2ga cable from the battery to one of the starter's mounting points. Once those were in place, the starter had no problems spinning the engine.

* I ditched the stock oil pressure sender in favor of my oil

* Replace the chassis's passenger side engine bay harness (the one with the ECU plug) with the one from the 5.0 donor car. - You will notice that the donor car's engine bay harness has no provision for the CCRM (the module just behind the headlight that integrates relays for the cooling fan, PCM, fuel pump, and A/C compressor clutch). Ditch the chassis's CCRM.

* Install the 93 ECU.

* Wire up a fuel relay + switch for the fuel pump. The EVTM is especially helpful here. For a street car, you will want the control wire to be hot when ignition is turned on so grab one at the ingition switch. For a track car, I have this wired to a switch. Control power goes to a switch when when sent to ground activates the fuel pump circuit. In my car, I already had a switch that brought the wire that originally went to the fuel shutoff inertial switch so I just rewired that to a relay. Power came from two dedicated lines I ran from the power junction box.

* If you went with an electrical fan, wire up a relay + switch for the fan. Ideally, I would have it deactivate itself above a certain speed but wiring in some kind of aftermarket vehicle speed sensor is going to take a little more work. I'm putting that on the future projects list. For now, it's a manual High Speed only fan.

* Hook up the driver's side O2 sensor to the engine harness.

* There are two coolant temp sensors on the coolant crossover pipe that goes to the heater core. The single wire one is for the HVAC system and the two wire one is for the ECU to tell it when the engine is up to temp. You only need the later one if you don't have an HVAC system. I also had a third temp sensor for my aftermarket water temp sensor. One problem I encountered was that the ECU temp sensor got in the way of the distributor cap when you cut down the coolant crossover pipe an mount it backwards (with the outlet aimed at the water pump). THe solution I found was to put the aftermarket temp in this position and screw the ECU temp gauge into the thermostat housing.


* On the Passenger side engine bay harness:
- Connect the engine harnesses two plugs to the passenger side engine bay harness.
- hook up the passenger side O2 sensor. Note: there is a 1-2' extension harness that connects between the passenger side engine bay harness and the sensor itself.
- Connect the 93 ignition control module to the harness. I had to drill a new mount point on the side of the wheel well's inner fender.
- Connect the MAF to the harness

* At the ECU plug, there is an input signal that tells it that the fuel pump is active. Without this signal, the ECU will NOT attempt to tell the ignition coil to fire. Obviously, you want this to happen so you need to feed pin 8 on the ECU plug 12V.

* Finally, there is one last plug that you will need to hook up: C156. This connector is not the same between the 93 passenger side engine bay harness an the 95 chassis so it stumped us for a while. Near as we can figure it, this plug connects the passenger side engine bay harness (and therefore the ECU) to the ignition module. There are 6 wires but they weren't well documented. I acquired the proper plug to mate to the 95 chassis from the 95 passenger side engine bay harness.
- Yellow passes through to existing connector 156 on 95 chassis
- Black passes through connector to 95 harness
- Red/Light Green passes through connector to 95 harness (12V from harness to ignition coil)
- 2 Black/Light Green wires to ground
- R gets 12V power (goes to 2 pins on the PCM - 37 & 57; I believe this is to power iton)

* 93 Tbird Tachometer in 95 Tbird gauge cluster (it just plugs in). I re-used the 95tbird gauge cluster b/c it includes stuff that is chassis specific (like the ABS light) that doesn't exist with the 93 tbird's gauge cluster.

* UPDATE 2015: I found out in 2015 that my alternator circuit wasn't charging because of a mismatch in my gauge cluster vs the signal expected at the alternator (the 95 gauge cluster which I need for ABS does NOT have an alternator malfunction light whereas the 93 car does so the 93 alternator expects it).
- Basically, the alternator needed a 12V signal going through an incandescent malfunction light to tell it to start charging. Without it, the alt won't charge the battery and the car will die a slow death (it will run on battery power alone + whatever additional current trickles out of the alternator) but it won't be happy.
- The solution is to NOT use an LED for the alternator malfunction light (will limit the current too much) but instead, you need to wire a 12V signal into the Alternator control harness AND install two voltmeters (one at the battery and one at the alternator output). Any difference in voltage (if it's running below 14V when the car is on), tells you there's an issue with the battery, alternator, or both.
The voltmeters I bought:

TIP: As you can see, several of these new adaptation circuits require 12V power from the power junction box. I originally had all of these add on circuits attached to the hot side of the power junction box (left side of the 175Amp fuse) but that bolt was getting overloaded (too many o-ring connectors on it to effectively screw on the nute. The solution was that I went ahead and made my own power junction using one of the 93 tbird starters (has a big bolt and adequately isolates itself from ground). All of the extra circuits now connect there and this whole mess is in a plastic box I bolted down in the area previously occupied by my battery.

Before Starting the Engine:
- Prime the oil pump by using a drill. I took a 1/4" drive 1/4" sized socket, ground it down as thin as possible, and jbwelded it to a long 1/4" extension I got as part of a kit from Harbor Freight. Spin it up and make sure that your oil pressure isn't excessive (a proper oil pressure gauge helps here) before attempting to start the car.

- Find TDC and insert the distributor so you are close.
- Pull the spark out connector (on the passenger side engine bay harness near where it pops out of the firewall).
- Set timing
- Burp out any air and Break in the engine if needed

Surprisingly enough, once I had the extra ground lines installed and once i had timing set, both the hard to crank and the the hot start issue (where the engine wouldn't start if it was warm) disappeared. I had no CELs (except for the "check gauges" light which I promptly disabled at the cluster) so this car runs spendidly.

If you are dumb enough to follow my path into 5.0 upgrade madness, here's a map.

Diagnostic Tips: Things to Test if Your Car isn't Idling Properly

* IACV: see if the engine runs any differently with the IACV plugged in or unplugged. I had to replace mine despite cleaning.

* MAF: clean it with MAF cleaner. Mine was filthy.
UPDATE 2017: Even if you think your MAF is a good one, if you are experiencing bucking/surging at partial throttle even after you have cleaned the MAF, try replacing it. We kept trying to diagnose a bucking/surging issue which prevented the car from being easily driven in the pits at pit speeds (but no problems at idle or at WOT on the track) and on a lark we tried the backup MAF. All issues went away. Bottom Line: Just because you cleaned your MAF and it's not throwing CEL does NOT mean your MAF is still good.

* Check for Vacuum Leaks: with a naturally aspirated engine, you can learn a lot with a simple vacuum tester (available for free loan from Autozone's Loan-a-Tool program). BTW: Besides looking for vacuum leaks, you can also test to see if you have too restrictive an exhaust system.

With the throttle body blocked off and the ignition coil + fuel pump disabled, I could test to see if I had any intake gasket leaks by seeing if bumping the starter will generate vacuum. This URL has a ton of other 302 engine specific vacuum tests to try:

Similar threads