1.8L Engine Swap
Written by Tom Lamano
I've just completed a 1.8 engine and wiring harness swap into my 91 base model
(along with installing a FM turbo II kit) and thought I would document and share
my experiences. These observations were written down over a three month period
whenever I felt it was important to do so, so its not very
Last winter, I re-read Randy Stocker's article in Miata
Magazine and after communicating with Randy I felt confident this was a project
I could handle. I set out to find a 1.8 engine, at first considering a 1.8 out
of a 91 Ford Escort with just 5k miles. It's the same engine as Mazda's 1.8 and
the price was right. However, after calculating the cost of the parts necessary
to convert it from its front wheel drive configuration to the rear drive Miata
configuration, I felt it was no longer cost effective. I still think this is a
good source for 1.8 engines, but only if you already have another Miata 1.8
engine to cannibalize for the necessary parts. I ended up buying a 1.8 from a 95
Miata with 8k miles. I bought it from Mazda Toyota Recyclers (800-628-0918 ask
for Richard) in Oregon for a reasonable price and had it shipped to my driveway
in Charlotte, NC. The engine arrived in perfect condition, I highly recommend
Mazda Toyota Recyclers for anyone's used parts needs, I've used them many times
with no disappointments. At first, I was going to approach the swap the same way
as Randy, i.e. use my 1.6 wiring harness, ecu, and throttle body. My car was
Sebring supercharged at the time and I was going to install it on the 1.8 as
well. I began reading about the power output of Bill Cardell's FM turbo/ecu kits
and decided to sell the supercharger and get some REAL power. Bill had another
customer doing a 1.8 swap and FM turbo install so I didn't feel like the Lone
Ranger. That guy soon sold his car and stopped answering my emails so it was
Hi-O Silver after all! I ordered my FM turbo kit in mid-March, at that time, I
was going to use the 1.6 FM ecu. Bill suggested I put in a 1.8 wiring harness so
I'd be able to use his soon-to- be-available 1.8 FM ecu with built-in knock
detection and boost control along with superior sequential port fuel injection.
I took a look at the dashboard removal section of my Miata Enthusiast's Guide
and decided to take the plunge. I called Mazda Toyota Recyclers and asked about
the wiring harness from the car my 1.8 engine came from but was too late, it had
already been sold. This would come back to haunt me later, as you will see.
Luckily, I was able to track down another harness locally at R & R Sales and
Service (704-892-4869). I went over to talk to the owner Ron Young, the harness
Ron had was in a front end wrecked 95 Miata, with an unusable airbag system
(deployed bags). I planned on removing my airbag and installing a Momo
competition wheel anyway so I made a deal with Ron where I swapped him my airbag
for his 1.8 wiring harness with the condition I remove it from the wreck myself.
I practiced on my car first by removing the dashboard, it took about two hours.
I had a week's vacation scheduled the next week, and went over to Ron's place on
Monday morning. We drove over to his storage yard and flatbedded the wreck over
to the shop. It took me about and hour to remove the dashboard, and another 3
hours to remove the harness. I labelled everthing and took lots of pictures. I
also removed the dashboard harness from the wreck after determining it was going
to be required to match up to certain connectors on the main harness. I ended up
buying the 95 instrument cluster from Ron to complete the electrical package.
Here are some dashboard removal tips:
The next day, I pulled my 1.6
engine without the trasmission, which seemed easier at the time, but made
installing the 1.8 more difficult. I recommend removing the engine/trans as a
unit, those top two bellhousing bolts are a bitch to remove with the engine in
the car. The next day, I removed my 1.6 wiring harness. With the dashboard and
engine out of the car, this is an easy task. I now had the two harnesses spread
out on tables in my garage,two engines sitting on the floor, and the dashboard
sitting on my dining room table! My car would have looked more at home in a junk
yard.! I spent the following day making minor repairs to the 1.8 harness. The
headlight and sidelight connectors on the driver's side were badly damaged from
the wreck, so I spliced in the connectors from my 1.6 harness, they were the
same type. The next day, I put the 1.8 harness in my car. Most everything fit
fine with these exceptions:
- Remove the glove compartment before removing the dash, this will allow
easy access to the electrical connectors and climate control cables that need
to be disconnected.
- Remove the console and center portion of the dash which houses the climate
controls and radio. Spray some WD-40 into the sides of the eyeball vents
before pulling them out via the string or wire method.
- Disconnect the two climate control cables to the left rear and right rear
of the center section of the dash.
- Remove the lower steering column shroud, this will give you access to the
electrical connectors below the dash that have to be disconnected.
- No need to remove the steering column, just remove the two retaining bolts
and push the column down.
- Put duct tape on your directional and windshield wiper stalks so they
won't get damaged when the dash is lifted over them.
- The dash is a tight fit, you will have to exert a bit of force to free it.
- Once its free, don't immediately lift it out, be sure you've not missed
disconnecting any electrical connectors.
The 1.8 ecu harness is longer than the 1.6
harness since the 1.8 ecu is behind the passenger's seat on 94+ Miatas but is in
the passenger footwell on 90-93 Miatas. There is however, enough room in the
footwell cavity to coil up the excess ecu harness if your car does not have
The connectors attaching the driver's side end of the main wiring
harness to the harness going to the rear of the car were incompatible. My rear
harness expected one connector, the 95 harness had two connectors neither of
which matched my 91 connector. After consulting the wiring diagram, I determined
there were extra wires going rearward from the 95 harness that were not in my 91
rear harness. My car is a base model, practically optionless except for a/c.
These extra wires were for the driver's seat speakers, rear window defogger,
power antenna, etc. Ron Young let me remove the matching connectors from the
rear harness of his wrecked 95 and I spliced them into my car's rear harness.
The extra wires that did not match up were just taped off. Right about now
you're probably realizing how important it is to have the 1.8 wiring diagram.
IMO, it would be impossible to do this swap without it. I got away with not
buying the 1.6 wiring diagram because Mike Hayes, the service manager at
Montgomery Mazda (704-563-1510) here in Charlotte, was good enough to let me
look at their manuals . Budget in another $50 into your engine swap project and
buy the 1.8 wiring diagram. BTW, Montgomery Mazda has the best service
department I have ever used. They replaced the timing belt and front crank seal
on my early 91 (weak crank) 14k miles ago and I never had any problems with
The 1.6 a/c relays connector did not match the 1.8 wiring harness.
Sometime after 1991 (1994?), a separate small a/c harness was added to the front
of the engine compartment on the passenger side. I was able to get this harness
and relays from Mazda Toyota Recyclers. The connector going to the a/c pressure
switch did not match though, so I spliced the 1.6 connector into the newly
acquired a/c harness.
The wiring harness connector going to the coils
harness on the 1.8 engine did not match. The main wiring harness connector had 4
pins, but the coils harness connector was a 6 pin type! My wiring diagram showed
the 6 pin connector. I drove down to Montgomery Mazda and looked at the 94 and
96 wiring diagrams. It turns out, Mazda changed over to the 4 pin connector and
different coils in 4/95, so I had a wiring harness from a car built during or
after 4/95, and an engine from a car built before 4/95! Fortunately, Ron Young
let me swap my coils harness and coils with his 95 wreck. The moral here is get
your wiring harness from the same car the engine came out of.
I tried to
mount the 1.6 crank pulley on the 1.8 so I could use the 1.6 alternator, but it
wouldn't fit. My 1.6 engine is one of the early ones with the weak crank. The
later style may fit, but I ended up buying a used 1.8 alternator from another
fine recycler, Mazda Recyclers in California (916-635-5900). The 1.8 alternator
is physically larger than the 1.6 which must mean its more powerful due to more
windings. I did have to widen the alternator harness ring connector with a drill
because the mounting bolt on the 1.8 alternator is larger also. If you decide to
use a 1.6 alternator, you'll also need a 1.8 mounting bracket.
went in with help from my friend Wayne Walling. As mentioned earlier, I left the
transmission in the car when removing the 1.6. This made putting the 1.8 in very
difficult. It took us an hour to finally get it seated properly. We ended up
having to remove the driver's side motor mount to get the engine in. Mounting
the starter and tightening the bellhousing bolts was tough also. Much of this
could have been avoided by removing and installing the engine/trans as a unit.
BTW, the 1.6 starter motor mounting bracket does not line up with the hole in
the 1.8 block. It must be replaced with a 1.8 bracket. Roebuck Mazda has them
I swapped my 91 speedo, oil pressure and gas gauges into the 95
instrument cluster for these reasons:
Some of these swaps may not have been necessary, but I
really didn't feel like experimenting. I took the opportunity to clean up my
audio system wiring at this time. The place that installed my cd player 4 years
ago really butchered my factory wiring. replacing the dashboard harness allowed
me to eliminate the butchered wiring and replace it with a plug compatible Mazda
specific harness purchased from Autozone for $8.
- My 91 has a 4:30 rear end ratio, 94+ cars have a 4:10 ratio, I wanted my
speedo to be accurate.
- The 91 oil pressure gauge is more accurate than the idiot 95 gauge. BTW,
you must also swap the sending units.
- My 91 has a smaller gas tank than 94+ cars using the 91 gas gauge insured
When I installed my Momo
wheel after re-installing the dashboard, my horn would not work. I discovered
the horn wire attached to the clock spring connector behind the steering wheel
first goes to the airbag connector on the passenger side of the car. Since my
car does not have a passenger side airbag, this connector is not used therefore
the horn wire signal ends there. This connector is was not accessible with the
dashboard now reinstalled so I routed a wire directly from the horn relay in the
engine compartment to the clock spring connector horn wire. Problem
The a/c compressor is now closer to the front sway bar. I was
able to give it more clearance by loosening my JR sway bar mounts and sliding
them forward in their elongated holes. I now have 1/2 inch of clearance between
the sway bar and a/c compressor. My a/c is presently not working due to low
freon, I'm thinking about converting to R134A, someone told me you need to swap
the receiver/dryer to do it however.
Here are some other points to
Here are some observations from my FM turbo installation:
- Buy the engine and all the parts necessary to do the swap at the same
time, going back to the recycler later will be more expensive.
- Buy the wiring diagram manual for the year car your 1.8 engine and wiring
harness came out of.
- Be sure the engine and wiring harnesses came out of the same donor car.
- Give yourself plenty of time to do the swap, I did it over a period of
three months mainly because I was waiting for my turbo to be delivered.
- Pull the 1.6 engine/trans as a unit, it will be much easier to work on it
out of the car and will make installing the 1.8 a LOT easier.
- Buy only Mazda radiator and heater hoses. They're pre-formed to the
correct shape, will not kink, and take up the least amount of room.
- Label and bag everything and take lots of pictures.
- Most, if not all the electrical connectors in the wiring harnesses are
different, thus making it very easy to connect everything correctly.
Here are some
additional mods made during the swap:
- No need to cut off your stock fuel injector connectors. They come apart
very easily by first removing the white plastic retaining clip with a small
screw driver, then pushing the metal connectors out the back while raising the
tiny plastic tab holding each connector in place. Place some shrink tubing
over each metal connector and push them directly onto your 560 cc injectors
using needle-nose pliers. The fit will be very tight.
- My air filter did not extend completely into the cold air duct, I drilled
two new mounting holes for the duct further to the right to allow the air
filter to extend fully into the duct. Access is limited from below to thread
the nuts onto the mounting bolts. Try gluing the nuts to your middle finger
with contact cement to help you reach the bolts from underneath. I've used
this technique in many situations where there is no room for two fingers much
less two hands. Putting some on the tip of your screwdrivers to help start
screws in tight quarters works great also.
- I filed a slot in my ecu housing for the keypad cable so the cover can be
screwed on completely without damaging the cable. Since the housing is
aluminum,it only took five minutes.
- All the exhaust manifold nuts are accessible with a standard 14 mm wrench
from above and below despite what the instructions say. I think they were
originally written for the 1.6 kit and modified for the 1.8 kit.
- My cold air duct hits the hood when its closed, I put a piece of vinyl
door edge trim on the duct edge to protect the powder coating.
- My tach does not work. Bill says its because the ecu was designed for 94
and early 95 engines. The coils having changed in 4/95 (see above). Link is
working on a fix. Bill Lackey has gotten around the problem by designing and
building his own driver circuit.
- I have a backfire in the intake when turning the key on after leaving the
car overnight, Its scary, but Bill says its harmless and Link is working on a
fix. I mounted a fire extinquisher on my Hard Dog sport diagonal bar just in
- My car smokes occasionally after a spirited run, probably due to not
enough slope in the turbo oil return line. I'm going to put a 90 degree
fitting in the line after it exits the turbo to increase the slope.
- I haven't done any ecu tuning yet because of the inoperative tach, but my
a/f gauge reads rich all the time, even at idle.
On the evening
of July 8, 1998, I put in Mobil-1 and coolant, connected the battery, reloaded
the default values into the FM ecu and turned the key. The engine started on the
FIRST crank! We took the car off the jackstands and drove around the
neighborhood (sans hood). That's about it, its been on the road ever since (with
hood). This was the most involved automotive project I've ever attempted, but it
was not difficult. Being just a hobbyist mechanic it was slow going at times.
I'd probably starve if I had to make my living as a mechanic. I hope this helps
anyone else who might be considering a 1.8 swap; if I can do it so can you. I'll
be out on the interstate trolling for Porsches, but feel free to contact me if
you have any questions.
- Installed a Moss oil cooler to the right of the passenger side grill area,
in an inverted postion. This required shortening the oil lines going to the
cooler and using 90 degree BPS fittings. I got the fittings from B.A.T. in
Florida, they advertise in Grassroots Motorsports. I also had to fabricate a
- Replaced my radiator with a two row automatic unit, cost $125 locally.
- Installed a FM kevlar clutch and have just over 900 miles on it now. It
engages close to the floorboards and has a little stronger pedal feel than the
centerforce it replaced. I haven't done any hard starts with it yet.
- Installed a FM turbo exhaust and hi flow cat, very high quality and good
- Installed a Cannon rear suspension brace. Initially it interfered with the
turbo exhaust but I was able to clear it by bending the exhaust system
- Installed a Hard Dog sport rollbar with diagonal and harness bars. The
hardest part of this job was cutting the interior trim pieces to fit around
- Installed a Greddy strut tower brace. Earlier versions of this bar may
have been poorly made, but mine is very good. I did have to polish the end
links on my bench grinder polishing wheel however. I also painted the mounting
brackets silver to better match my car. The bar costs $100, and is well worth
it for looks alone.
- Had my cam cover polished locally, cost just $50.