What regulates the voltage to injectors?

[vas deferens]

I wuz wunderin what regulates the voltage to the injectors?....the TDC?......RPM sensor?.......DME?......anyone out there in cyber automotive pergatory know?.....If there is no voltage firing the injector I would like to know where the fasted, cheapest, and simplest place to look would be......ciao

[Mrmerlin]

Originally posted by vas deferens:
I wuz wunderin what regulates the voltage to the injectors?....the TDC?......RPM sensor?.......DME?......anyone out there in cyber automotive pergatory know?.....If there is no voltage firing the injector I would like to know where the fasted, cheapest, and simplest place to look would be......ciao

The DME is responsibly for the timing of the injectors if your not getting any voltage then I would look at 1 the engine ground for the injector harness in the rear of the cyl head , 2 the DME relay or fuel pump relay, also look to see if there are any other corroded relays in your panel just pull them out and reinstall (if it is not indicated in the fuse panel as a DME relay)3 if all looks good then check the engine speed sensors and remove them and clean em 4 get another DME box and plug it in to see if you get voltage........Stan

[Kaos]

I'm not exactly sure how the 944 injectors are rigged up, but I know that ALL modern cars use what is called a "low side driver" to run the injectors from the processor.

What this means is that the control of the injectors is performed when the processor grounds the low voltage side of the injector. So, the hot side of the injector (+12V supply) is always hot, regardless of the current firing status of the injector.

When the injector is not firing, the processor internally uses what is called a "pull up resistor" which creates +12V on either side of the injector (for a net 0 voltage).

Because of this system, a noid light is required to determine if the wiring to each injector is OK. You can buy one of these noid lights from your garden variety parts store for about $5. Just unplug your injector, plug the noid light in, and crank the engine. If the noid light blinks, then the wiring is OK. Check all of the injectors. If none of the injector wires are causing the light to blink, then there is probably something else wrong, like a bad relay, or a completely smoked processor.