Just want a confirmation on power at relay (4-pin) #1 and #3 Options

[Downerman]

So just to be clear. With the Key on.... On the white four connector (Pulled off) on the relay board, Pins I and III. I have 12V+ which means I'm carrying and confirmed 12V+ at the ECU plug on pins 16 and 24 from white 4 connector pin I . In addition Pin 19 on the ECU also has 12V+ from white 4 connector pin III - WITH KEY ON.

Whats happening is I'm not getting a ground from pin 19 ECU back to 4 wire connector on relay board, number III, to pin 86 of the fuel pump relay, as to flip the relay and give me that 2 second pop of the fuel pump. If I take a small wire on the fuel pump relay #86 and ground it I have power on main cabin connector/Relay board pin 13...AKA fuel pump. All relays tested (headlight trick). Using one of the docs on Jeff's site "Porsche 914 Fuel Pump Troubleshooting" and I fail #12 which tells me I have a faulty ECU. Mine was beat... car was a basket case and now fully restored. Got a used one and same issue. Continuity is perfect everywhere - New Bowsley wiring harness (Engine area). I will spare your the other 21 steps but I pass them all except power to the dang Fuel Pump....cuz #87 never get's the signal from III

Here's #12:
12 Test: ECU control circuit
Key off:Test continuity from Pin III on white 4 pin connector plug at Relay Board to ground (white plug harness un plugged from Relay Board. ECU harness plugged into ECU).
Key on: Continuity to ground for 1.5 seconds = good ECU control cuircuit.
Key on: No continuity to ground for 1.5 seconds = faulty ECU control cuircuit
(The ECU grounds Pin III of the white 4 pin connector on the Relay Board to run the fuel pump for 1.5 sec. at key on)

I'm just trying to understand why I have 12V on III with key on. Which means 12V to pin 19 ECU and I don't want to fry something.

Dave

[jcd914]

Actually you are chasing a problem that doesn't exist, 12v at pin III with key on and the plug removed is not a problem.

When you turn on the key the power supply relay closes and allows battery power to go to the fuel pump relay terminals 30 and 85. Then when terminal 86 is grounded the fuel pump relay engages and allows power from terminal 30 to go to terminal 87 and the fuel pump.

In the fuel pump relay, terminal 85 is connected to terminal 86 via the engagement coil of the relay. So if there is battery power (12v) at terminal 85 there has to be power at terminal 86. It is this 12v power at terminal 86 that the control unit grounds to engage the fuel pump relay. The relay itself won't flow enough current to cause any issue (probably milliamps). If you were using an old school analog voltmeter it probably wouldn't read 12 because the meter would have consumed most of the current flowing through the relay.

Have you verified that power from terminal I on the relay board is getting to the FI control unit?

Good luck
Jim

[Downerman]

Actually you are chasing a problem that doesn't exist, 12v at pin III with key on and the plug removed is not a problem.

When you turn on the key the power supply relay closes and allows battery power to go to the fuel pump relay terminals 30 and 85. Then when terminal 86 is grounded the fuel pump relay engages and allows power from terminal 30 to go to terminal 87 and the fuel pump.

In the fuel pump relay, terminal 85 is connected to terminal 86 via the engagement coil of the relay. So if there is battery power (12v) at terminal 85 there has to be power at terminal 86. It is this 12v power at terminal 86 that the control unit grounds to engage the fuel pump relay. The relay itself won't flow enough current to cause any issue (probably milliamps). If you were using an old school analog voltmeter it probably wouldn't read 12 because the meter would have consumed most of the current flowing through the relay.

Have you verified that power from terminal I on the relay board is getting to the FI control unit?

Good luck
Jim

Yes.... pins 16 and 24 on ECU. so your saying at key on I should have 12V on III and 12V on (I)? Maybe I'm just daff which sometimes I do amaze myself but if I have 12V at III and 19 on ECU sends a ground signal over to III that there would not be some issues?