Nobody ever claimed that the Z32 Nissan 300ZX Twin Turbo was a reliable vehicle. Here’s one of the reasons why.

Imagine a perfect, sunny, 70 degree day. A faint breeze caresses the air while the surrounding foliage is beginning to give way to fall’s beautiful hues. What a wonderful opportunity to take the old 300ZX out for a spin. T-tops off, sunglasses on, music locked in, and turbos spooling as you blast down the highway. The car is a mechanical beast in harmony with nature, and you’re present to orchestrate it all. “Life is good!”, you think.

Unbeknownst to you, your 300ZX has other plans in the works. This is a car that loves to build up your confidence, only to be waiting for the perfect moment to slam it straight into the ground. It’s a reality that’s bound to happen—it’s simply a matter of when.

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For me, the when happened sooner than I anticipated. It was like a light switch - one moment the engine was running freely like a thoroughbred steed, and the next it was coughing like a mid-2000s Civic that just ejected a spark plug.

I’ve replaced nearly everything on this thing, so I wondered, what could possibly be the problem now? Thankfully I found myself only two miles from home, so I limped the sickly vehicle back to the garage. It was time dive into diagnostics once again.

The Doctor Is In

Right from the get-go, I knew that the loping, rough-running symptom could only have meant that one thing: A cylinder wasn’t firing. The task at hand was to determine which one, so I started the engine up and dug deeper into the diagnostic process.

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One by one, I unplugged each coil pack to locate the non-functioning cylinder. When I pulled the coil connector off of cylinder six, the sound of the engine didn’t change. Bingo! Now I needed to figure out why the cylinder wasn’t firing.

I removed the spark plug from cylinder six and it looked brand new. It didn’t have many miles on it so that made sense. However, from a diagnostic standpoint, the plug’s observed condition didn’t matter. I needed to rule the plug and its corresponding coil pack out of the pool of potential suspects. I verified the coil’s connector was getting the correct voltage, so I knew there wasn’t a wiring issue going on. I installed the plug and coil pack in different cylinders while placing known-good components back in cylinder six. I fired the engine back up; still a misfire, and still on cylinder six. So much for hoping for an easy ignition repair.

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Next stop on the diagnostic train was the fuel system; more precisely, the fuel injector for cylinder six. Now, it’s no secret for those familiar with ‘90s Zs that the fuel injectors are a common failure point. However, I replaced the fuel injectors during the original overhaul of the car. Surely one hadn’t failed in the 3,000 miles since then.

Checking the injector’s resistance.

I hooked up the voltmeter to the suspect fuel injector, set the meter to ohms (to measure the injector’s electrical resistance), and found what I thought I might find: A reading of “1.” In voltmeter-speak, this means zero continuity through the circuit. In other words, this meant the injector was kaput. Great!

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Making An “Investment”

When I originally overhauled the car, I installed “old style” injectors. These injectors have actuator coils which are exposed to fuel flowing through the fuel rail. The actuator coils on these type of injectors tend to go bad when they come into prolonged contact with ethanol-spiked fuel. Well, I guess this situation just happened to me, and it only took 3,000 miles. Damn.

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Luckily, there are “new style” injectors on the market that guarantee that this ethanol-induced failure would no longer occur. I had no choice if I wanted long-term reliability from the car; I needed to cough up the money for these new and improved units.

Keeping in the spirit of “future proofing” the Z, I decided that I might as well install larger 740cc injectors to allow for more precise fueling and better tuneability. I also bit the bullet and elected to install a secondary mass airflow sensor so that the car’s aftermarket dual air intake system would no longer consist of a hodgepodge of vacuum lines. As it turns out, this setup had been compromising the car’s low-speed driveability.

The old dual air intake setup.

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Coming full-circle on this financial disaster, I also picked up a reprogrammed ECU chip which would allow the car’s computer to handle the new injectors and additional mass airflow sensor. I figured if I was going to dig into this engine bay again, I might as well do it right and be done with it.

(If you like videos, then you’re in luck. I made one of the repair. Check it out!)

The Teardown

I don’t know how many times I’ve torn away the upper portion of this car’s engine. Every time I’m faced with the task, I think, “Where do I even start?” There are so many vacuum hoses, coolant lines, electrical connectors, and bolts to be removed.

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I’ve found there isn’t a “most efficient” way to do it. Just be methodical, and double check that everything’s been disconnected before yanking up on the intake plenum. I’ve done alright so far by following that mindset.

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With the plenum out of the way, I could finally see the fuel rail and all six injectors that were bolted to it. In the back corner was the reason this whole event was unfolding - injector number six.

I pulled the fuel rail out of the car and sat it next to the pile of parts collecting on the garage floor. I hoped I could remember how it all went back together.

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I sat the fuel rail on the work bench and gave it a cursory look-over. From the outside you’d never guess that anything was wrong with one of the injectors.

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I proceeded to remove the old fuel injectors from the fuel rail as I wouldn’t be reusing any of them. Just when you think you’ve completely drained the fuel rail of gasoline, more spills out of some hidden cavity within. No matter how much you try to avoid it, you’ll end up smelling like gasoline during this job.

With the fuel rail relieved of the old injectors, I had arrived at the final disassembly point. It was time to take inventory of the new parts.

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Parts Special

Ordering a set of injectors, a mass air flow sensor, a translator unit, an ECU chip, and some spark plugs was not exactly a modest outlay of funds. So when the parts arrived in a package no bigger than a shoe box, I was a little disappointed. I wanted the money spent to be represented by something much more substantial! Alright, so maybe that’s a bit adolescent. Regardless, inside this relatively small box was just what I needed to make my car work correctly again.

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Before throwing the new parts into the car, I took some time to analyze them. I enjoy spotting the differences and improvements over the old parts’ designs.

Okay, enough science. Daylight was burning and it was time to get this complicated thing back together.

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Assembly Line

The first item on the reassembly checklist was to install the new injectors into the fuel rail. I slipped new o-rings over the injector bodies, applied a thin layer of oil over the o-rings, and popped the injectors into the fuel rail.

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With the new injectors secured to the fuel rail, I flipped the rail over and fitted some new rail-to-intake manifold insulator seals.

With the new insulator seals installed, it was time to fit the fuel rail back to the engine. I then offered up a new plenum gasket to the intake manifold.

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Before proceeding on to the hellscape of reinstalling the intake plenum, I decided to rest my mind a bit by doing an easy job first: Fitting up the new mass air flow sensor and translator unit.

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The installation of the secondary mass air flow sensor and the translator unit was as easy as they come. The translator’s harness simply hooked up to the original mass air flow sensor’s connector. Job done!

Now commenced the painfully slow and frustrating process of reinstalling the intake plenum. Removing the thing is a breeze compared to putting back in. There are numerous hoses that need to be slipped onto the plenum’s vacuum ports at the exact same time. Once the plenum is seated, there is no room or maneuverability to attach the hoses after the fact. Then comes the numerous branches of wiring harness that must be routed just so. Good times all around.

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If you look closely, you’ll find there are less vacuum lines present compared to before.

With my patience wearing thin, the plenum finally fell into place. What an ordeal! The final piece to the puzzle was to install the new ECU chip. This was my first-ever attempt at installing an ECU chip and I was a little nervous. The pins protruding from the chip which slot into the ECU are thin and fragile. It would be really easy to screw this up.

Hey look, it has a name!

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With the cover plate removed from the ECU, I saw the circuit board where the old chip was located. I gently pried the old chip from the circuit board. The chip slowly released its grasp and I let out a huge sigh; I was halfway done.

I knew that the directional orientation of the chip was critical. The semi-circular cutout in the chip needed to point toward the red LED. I aligned the chip pins with ECU’s ports. Applying a light amount of downward pressure, the chip slid into place. Just like that, the ECU was now ready to handle the new injectors and additional mass air flow sensor. Hooray for plug-and-play ‘90s technology!

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The Figures

740cc injectors, adapter kit & ECU chip: $998.00

Iridium spark plugs: $50.00

Mass air flow sensor & translator: $375.00

Plenum gasket & miscellaneous parts: $54.69

Labor hours: 16

Repair Total: $1,477.69


Unearthed Performance

Yes, I know. Holy crap, right? The Nissan 300ZX Twin Turbo is not an inexpensive car to put right. All that remained was to start the car up and see if I noticed any improvement.

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Turning the key to the “ON” position, I heard the fuel pump begin to power up. As the pump’s sound dropped from a high-pitch whine to a low-volume hum, I knew that the fuel system was now fully primed. I rotated the key to “START” and the engine stumbled briefly then coughed into life.

While the car warming up, I poked around in the engine bay to check for coolant leaks. I must be getting better at this because there were none to be found. Result! The V6 had settled into a satisfyingly-smooth idle. I was excited to get this thing out on the road.

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Backing out of the driveway and heading down the street, immediately I could tell a difference in the car’s low speed engine response. Gone was the rough climb in engine speed from lower RPM as well as the delay from the throttle pedal. That additional mass air flow sensor was working some magic.

Of course, the improvements in low speed driving were only part of picture. The new injectors, and the ECU tune that came with them, would be most felt when giving the engine the beans. Rolling onto the highway on-ramp, I let her rip.

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This car has always been quick. It’s never had a problem pinning you to the back of your seat when grabbing a generous helping of throttle. But, somehow, it’s even quicker now. There’s a tremendous power improvement through the mid-range. The biggest improvement, however, is felt at the very top of the tachometer. Previously, the car’s peak power would trail off after around 6,000 RPM. Now, this thing surges all the way to the 6,500 RPM redline - it just begs you to take it there. Without question, I am satisfied with this newfound performance.

Here I go again; swooning into the confidence-inspiring grasps of this car’s persona. It’s building me up just to let me down again. But you know what? I don’t even care. The Z is running great and I’m poised to enjoy it while it lasts. No one ever claimed these cars were reliable, but with the new parts I’ve just thrown in, I’ve given this ‘90s techno-marvel one less reason to complain.