INTERMITT. ENGINE MISS OR LOSS POWER-REPLACE FUEL INJECTOR

Affected: 1989-90 GRAND AM AND GRAND PRIX MODELS W/2.3L

A concern of intermittent engine miss on one cylinder or loss of power may be caused by an injector that has a decreased electrical resistance value.

On the 1989 and 1990 Quad 4 engine, the injectors are fired in pairs, see Service Bulletin 89-6-48 issued 5/89. The ECM transistors that control the firing of the injectors are current limiting. That is to say, the current in the circuit can peak to 4 amps then is reduced to 1 amp. This feature is referred to as "peak and hold".

If the electrical resistance value of an injector decreases as little as 0.4 ohms, (using ohms law) the injector will consume excess current from the ECM and leave little to drive the adjacent injector with the proper electrical resistance value. The cylinder with the good injector stops operating while the cylinder having the injector with decreased electrical resistance continues to operate. In other words, the injector in the "Dead" cylinder is good and the injector in the "live" cylinder is faulty.

The suggested diagnostic procedure is to make a list of the injectors driven by the same ECM terminal as the affected cylinder. Cylinders 1 and 4 are paired and so are cylinders 2 and 3. Measure the resistance of those injectors. Substitute the injector having the lowest electrical resistance with a "known good" part. Then re-evaluate the driveability concern.

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