Corrado Fuel Injection: A Different Digifant

Gear case (3)The very first 1990 Corrado fuel injection system on the G60 1.8 Liter engine had a different fuel injection system than the second year. It was a Digifant system that powered all 4 injectors through a single pair of wires. The 1991 Corrado fuel injection system had injectors that fired sequentially, and thus a 5 wire setup. Both models had possible issues with wires deteriorating right at the injector connector. The first system would strand the car, the second system would turn it into a 3 cylinder.

The G60 Corrado fuel injection system was not a good candidate for the regular MAF sensor to measure intake volume, so the fuel mapping was based on a quartz crystal type Manifold Absolute Pressure (MAP) sensor inside the ECU. Occasionally, the hose to the Engine Control Unit (ECU), or assembly inside the ECU, would leak and throw off the readings. The engines that received inadequate oil changes and thus worn down, would capillary oil droplets from the worn engine’s PCV system up inside the vacuum/pressure hose to the ECU and radically slow down the response time of the MAP sensor. This resulted in acceleration lags and poor mileage. The quartz crystal knock sensor would fry off its insulation just like any other Digifant equipped motor. Seepage from the supercharger hoses would deteriorate the oil cooler hoses until many of them burst.

Many customers installed power chips in their ECU’s, and since the EPROM chip was in a socket and could be changed easily, they could buy a couple of different programs and play around. Some even bought race fuel and would change chips just for a weekend of fun. With all the available modifications, Corrados were frequently way over 200 ponies. Some got way over 300 ponies. The G60 engine became a record breaker for horsepower per liter standards.

Sometimes a power loss during acceleration would occur due to a lean condition. There were several possible culprits. The above mentioned MAP system failures were one. Air leaks were another. A stranger cause comes from a fuel injection grounding issue. The ground behind the battery would get corroded, likely from battery acid. This could cause the ECU to falsely identify the signal from the oxygen sensor as being above the system’s nominal .5 Volt ECU output, as the actual ECU oxygen sensor output voltage would register as lower than .45 Volts at the oxygen sensor. The ECU output voltage would measure .5 volts at the body, but only .45 volts or less at the engine. The resultant oxygen sensor sine wave would then average too low, and then drive the mixture perpetually lean. This made for poor acceleration and lean misfire under power. To recap, a corroded fuel injection ground would cause the system to run lean. A tough problem to catch. Welcome to the Corrado fuel injection system.

Gear case (3)