Quote:
Originally Posted by johnnyxs
The ECU does not control the fuel pump and has no direct connection with it. Fuel delivery is controlled by the ECU (DME) indirectly, by pulsing the injectors
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Actually it does - the DME relay is 2 stages. The first stage provides power to the DME itself, along with the fuel rail and the auxiliary air valve. It is activated when you hit the ignition switch.
Then there's a second stage, which controls the fuel pump. The DME is in charge of activating this stage, which is important to know. It will activate when two conditions are met: 1) the DME has to be on, obviously. and 2) the DME has to see that the engine is spinning > 200 RPM.
So if there is no +12v at the fuel rail, start by looking at the relay or the wiring. Remember, you want to look for 12v between a GROUND and one of the pins on each injector connector, not 12v between the 2 pins. If you DO have voltage between the pins and chassis ground, the DME relay first stage is good.
The +12v to the injectors is actually constant, believe it or not. The DME controls the injectors by pulsing a ground to each channel. That's why you won't see voltage BETWEEN the two injector pins unless they're supposed to be firing, and you should use a chassis ground.
Going back to the part about sensing the engine speed, check out the sensors over the bellhousing and their connectors. That's what reports the engine speed and position to the DME and if it's not working, the DME won't activate the fuel pump.