Checking your injectors electrical circuits

You may have an injector fault and you wonder “Is it the wiring or is it the injector?”
Here’s an easy method to check the wiring to your injectors

injector circuit diag.JPG
12volt is constantly supplied directly to all the injectors N70 (wire MB in this wiring diag for a 1.6 Stilo MB = Brown and White)
And each injector timing is done by the ECU by supplying a path to earth
injector.JPG
An injector is a simple electrical solenoid valve which opens and closes the injector to spray fuel into the cylinder. This picture shows the actual connector on an injector which you can test for continuity using this method without actually needing to physically get at it

Just for reference here are the Italian wiring codes

N= BLACK
B= WHITE
C= ORANGE
M= BROWN
A= LIGHT BLUE
S= PINK
V= GREEN
R= RED
Z= PURPLE
G= YELLOW
H= GREY
L= BLUE

Ok Now each injector solenoid should be a closed circuit i.e. a continuous electrical path with no breaks so if we check the resistance of each circuit they should all be the same, on my 1.6 Stilo they were each 15 ohms. That's the resistance through the solenoid coil. The actual figure isn’t so important but that they should all be the same
injector D81 connector.JPG
Injector multi connector D81 just lever up catch and pull to disconnect

So with ignition switched off and a cold engine disconnect the D81 connector and using your multimeter check the resistance between the 12v supply pin and each injector pin. The 12v supply pin is easy to spot as it’s the extra large one in the centre of the 5 pins in there. Do each circuit in turn (always one probe on the 12v supply and the other on one of the other pins) and they should all be the same. No circuit at all (infinitely high resistance) or zero resistance would show a wiring fault or injector solenoid burn out.

Be clear what you’re testing here though, you are testing the integrity of the wiring circuit to the injector, the injector internal solenoid for continuity, the connection of each injector connector and the earth supply back to the D81 connector.