Hi folks hope someone can shed some light on this headache I have. was told ECU on car was faulty as car has misfire on cylinder 4 despite replacement injector. got the ECU sent away for diagnostics and repair, was informed by the chaps doing the diagnostics nothing wrong with ECU. ECU came back put it in car and now misfire cylinder 1 and 4, seems to be no pulse signal from ECU, but could someone who is an expert authority on ECUs explain if it possible for this to happen ie signal to 2 injectors present and 2 absent, if so what would cause this?

BTW car is volvo s40 v50 2.0 diesel it is a siemens ECU unit

Thanks in advance people :)

I don't know Volvo ecu but in other ecu, yes is possible. The injectors are often in two banks. eg bank 1 injector 2 & 4, bank 2 injector 1 & 3. With the right tools it should be possible to test injector output from ecu and follow it through wiring harness.

Hey

1. unplug injector and measure power supply on injector connector (ignition on)
- one pin should have 12 volts, if not check relay, fuse and wiring resistance
- if it has got distinctly less than 12Volts check wiring resistance to ground
2. unplug ECU and measure resistance and resistance to ground of the other pin (ignition off)
- wire resistance = 0 ohms
- resistance to ground = open line
- if not replace harness / fix shortcut

if there is still a problem, get a scope and ask again!
best luck!

note: often 2 injectors have a common power supply!

happened to me on a passat 1.6 siemens ecu also, but one injector only, in this case was the injector driver IC on the ecu board