1996 Mazda Miata With A Partially Installed Engine.
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This 1996 Mazda Miata showed up in the middle of an engine installation after the previous shop had run into issues they could not get to the bottom of and therefore could not complete the job.
Situations like this are common. Even very experienced shops can find themselves in situations outside their abilities because each vehicle out there requires mountains of specialized knowledge. This shop was very competent, but simply did not know Miatas that well. Once we got under the hood it was clear the install was far from done. The car needed a TPS, both coolant sensors, bleed the clutch, correct the engine misalignment, install the intake manifold brace, source and install the correct exhaust manifold and downpipe, along with various ground straps, wiring, and hoses had to be installed. Once the various loose ends were tied up, we could address the elephant in the room.
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Roll With The Punches.
In the process of sourcing a good, used motor it seems the previous shop found a low mileage engine from overseas. Most likely from the JDM side of things. This is a perfectly viable solution, but they unfortunately made the mistake of buying a 1.6l engine.
The 1996 Mazda Miata originally came with a 1.8L from the BP family of Mazda engines. This is commonly called the BPE8 in reference to the head design, but the engine is technically a BP-ZE. The engine was offered in the Miata from 1994-1997. The 1990-1993 Miatas came with a 1.6L engine called the B6ZE. It's from the B6 family of engines.
While smaller, the 1.6L engine is still an option. Old 1.6L and 1.8L engines from 1990-1997 generation cars swap back and forth relatively easily. However, it's not that simple this time. Upon investigation, we noticed that this 1.6L was not running the same hall effect ignition sensor as all 1990-1997 Mazda Miatas in the U.S.A. It looks like we have a bit of a wild card going on here, and we're beginning to see why the other shop gave up. Let's take a look.
The 1996 Mazda Miata originally came with a 1.8L from the BP family of Mazda engines. This is commonly called the BPE8 in reference to the head design, but the engine is technically a BP-ZE. The engine was offered in the Miata from 1994-1997. The 1990-1993 Miatas came with a 1.6L engine called the B6ZE. It's from the B6 family of engines.
While smaller, the 1.6L engine is still an option. Old 1.6L and 1.8L engines from 1990-1997 generation cars swap back and forth relatively easily. However, it's not that simple this time. Upon investigation, we noticed that this 1.6L was not running the same hall effect ignition sensor as all 1990-1997 Mazda Miatas in the U.S.A. It looks like we have a bit of a wild card going on here, and we're beginning to see why the other shop gave up. Let's take a look.
 When we look at a shot of the engine bay on 1992 1.6L Miata parked outside our shop, we can see there's no ignition sensors on the front of the engine.
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While at the back of the engine we have a combined crank and cam angle sensor. This sensor uses either a magnetic or optical signal based off a shutter wheel inside to let the ECU know the position of the crank and the cam shafts while operating. The new engine is different.
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We CAN see two ignition sensors on the front of this engine. The badge means its officially JDM. It's a 1.6l from a later model NB Miata. Fun fact. Using Google translate we can see this badge recommends changing the timing belt at 100k kilometers, or about 60k miles. American Miatas of this generation (1999-2005) will tell you to chance them every 100k miles. That's a lot more miles. Older Miatas also say change your belt at 60k miles. Ignore the updated maintenance on American cars. It a way to make projected maintenance costs cheaper when manufacturers are selling new cars. Change timing belts at 60k miles.
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Time To Up The Ante
The 1.6L engine now installed in this car is not like an early 1.6l engine in several ways. The key difference for our situation is that it has different cam shafts. We might normally consider taking the intake cam shaft out of an older Miata and installing it in this engine. That would let us run the original CAS sensor seen in earlier Miatas. However, the cam profiles would be different, and the old cam shaft uses hydraulic lifters. The modern 1.6l currently installed uses mechanical lifters. We could go to the trouble of changing out the cam shaft and replacing the hydraulic lifters with mechanical ones, but we don't know the consequences of running a cam shaft with a different profile with the stock ECU and we don't know the consequences of running mechanical lifters on half the engine. Chances are we would run into more issues. It seems more straight forward, and ultimately cheaper, to simply install a programmable computer that can handle the engine we already have. The owner has plans to maybe run a turbo in the future anyway, and he would need a programmable ECU to do that properly.
Enter The Megasquirt
Megasquirt is always the answer. Follow along in the gallery for this part of the process.
Never That Simple
So that's it, right? We've installed a programmable ECU capable of running either ignition sensor system, we've correctly modified the wiring, and we've installed the new sensors. It should fire right up? Yes, it should. It doesn't. It sounds like the timing is off, but mechanical timing has been verified and compression also looks nice and healthy. It's something else. Let's take a look.
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Even though the car does officially crank up and run, the cranking process is extremely long, and the car struggles to fire up. The crank signal has been strengthened and cleaned up, but it needs more help.
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It's not really clear why the signal is so dirty. The wiring is good, it has additional noise shielding beyond even what the factory used, the method of wiring up the sensors is sound, and the noise filtering should take care of the rest. As a last step, a different trigger wheel is installed on the crank. Instead of only 4 individually spaced sensor teeth, this wheel has 36 teeth and a gap the size of two teeth. It's 36-2. With this final addition to the installation, we have full cranking success.
This more refined trigger wheel gives much more even and clear signal inputs to the ECU. Another advantage of a programmable ECU is the ability to add and change things like this as needed. If we were relying on the stock ECU, we would have been stuck with nothing left to try.
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Finally Done. What Did We Learn?
This car is finally running, but it still needs to go to a tuner for a real dyno tune, drive-ability tune, etc. One older cars, once you start getting even a little outside the norm on modifications, it's a great idea to invest in a programmable ECU. This ECU should be capable of handling a turbo or a different engine in the future, and helps keep older cars like this up and running. It can be an investment, but it's typically worth it.