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We received a form regarding a rare GSL-SE that requires some TLC and an engine rebuild due to its starting issues, rough running, stalling, and overall unreliability.
Or does it?
We like to lead with a proper compression test on most of our customer cars (unless the engine is physically damaged internally).
Why? Because this is the best way to know how the internals are. Compression is best when apex / side seals are properly clearanced, carbon deposits minimal with good oil control rings. The only better way is to tear the engine down and properly inspect / measure.
What did we find? The engine compression was down, plugs were fouled along with high levels of carbon build up (after we put our HD scope into the combustion chambers.
These vintage Mazda Rotaries often endure long periods of inactivity, which can result in a host of corrosive consequences. Rust and degradation never seem to rest, even when everything else does..
Because the compression numbers were consistently low, we decided to use (a tried and true) procedure to restore compression without taking the motor apart. The majority of engines we see will not benefit from this, however, after building / racing rotary engines for years, once in a while, it is our first preferred method to restore compression.
We were able to get the compression back up after 4 cycles (using the right solvents/lubricants) and the numbers were all over 120psi. Next, we got the car running with fresh plugs, fuel and testing of the ignition system. With the engine running, we can see that it is running rich, the idle is hunting up / down and it soon stalls with spark plugs fouling.
Now, what is next?
Back to the diagnosis. From here we get out the data sheets and go through wiring diagrams checking for proper operation. The first and obvious find is the lack of a working O2 sensor in the exhaust system and the air temperature sensor is broken. This car, originally from New Jersey had been modified with a header / exhaust system. Further inspection shows that the header is past its useful life and needs replacement along with needing a working O2 sensor. A car with these symptoms may run adequately at sea level, however here at our altitude, proper fuel / air ratios are critical for smooth operation
Pull the intake, remove all of the components on the top of the engine to further our inspection /. findings.
Now, we take the ultrasonic up to temperature and clean the intake system, fuel injectors and six port actuator system. Running rich means that carbon build up is going to be high. With all these components clean, we inspect, clean, and test for operation. With a new header / O2 sensor and pressure tube for activating the secondary ports, the car has a better chance to work properly.
Moving forward, we proceed with upgrading the cooling system by installing a Koyorad radiator with higher capacity and efficiency, along with a larger oil cooler equipped with -10AN stainless steel braided lines..
Having full fabrication skills is necessary for building a proper oil cooler mount. Location of the oil cooler is critical for getting air to pass through.
Now that we have the motor running better, the next is to see how it runs at temperature. One thing noticed is the engine is still running rich with new O2 / IAT sensor, further inspection, the coolant temperature sensor isn't working properly, it remains at high ohms telling the computer that the engine coolant temperature is near zero degrees.
This means that the car still thinks the engine is cold and needs to warm up. Because the coolant sensor is no longer available, time to find an alternative and install (checking / repairing wiring harness).
The car now starts right up, idles correctly and pulls hard to redline.
These cars are getting rare and need proper care to bring back to life.
Expertise is crucial in situations like this. By investing time in accurately diagnosing the issue, we were able to determine that the owner's car didn't require a completely rebuilt engine. Instead, it needed to be repaired in the correct manner, with a thorough diagnosis and the replacement or repair of only the necessary components..
Customer came to the shop for the test drive. After having the car here in Colorado for many years, it now gives him the smiles desired and is ready for carving up canyon roads and the occasional track days at High Plains Raceway.