Updated 8/10/98
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 exceptions:

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 it.

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.

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 solved.

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: Here are some additional mods made during the swap: 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.


Tom Lamano