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 organized.
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
- 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
- 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 ABS.
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.
The 1.8 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 for $11.
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 remember:
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
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
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 case.
- 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
- 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 mounting bracket.
- 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
- 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.