Really don't see that many failed computers. Or problems with injectors either, except on GM products.
You WILL have very low voltage on the ground side of the injector. If you measure that wire with the injector plugged in, you'll find full battery voltage on both of them. The voltage appears on the ground wire because it's coming through the injector. The computer grounds that wire when it wants to turn the injector on.
There's more to testing an injector than the resistance tests. For that to fail, a wire inside would have to corrode or break off, which isn't likely, and the open circuit would be easy to identify. They aren't likely to short because the terminals are too far apart. Some of the adjacent coils of wire could short, and that would affect how the valve opens. If you were to watch the current waveform on an oscilloscope, you can actually see the little hump where the valve moves off its seat. That is part of the strategy of how the Engine Computer watches for a problem. That won't show up with a resistance test because the industry standard of plus or minus ten percent is okay so it can be normal to find a half ohm difference between two good injectors. The better alternative is to swap that injector with one of the other ones, then see if the fault code sets for the other cylinder.
Resistance tests also won't show up an intermittent electrical problem inside the injector. Since it is a coil of wire, it is going to develop a voltage spike when current is suddenly turned off. If some of the coils of wire are shorted out, that spike will be lower than normal. Also, if arcing has taken place inside the injector between some of the loops of wire, a carbon track will be left behind. That is conductive and will make it easier the next time for a spark to occur there. Often the injector will still open normally with 12 volts, but that spike will be partially-shorted out, and the computer will interpret that as a defect.
Feb 20, 2014 at 5:22 PM
