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

Oh yeah.... 1973 2.0

What is the failure? Fuel pump not working, won't start fuel pump operating, etc. I understand the test you are running but not what the problem is that you're trying to solve

Hmm, I thought I did in the "What's happening is:" in original post. but I think admittedly, a long winded approach. No juice to the fuel pump (tested).

If you jumper the pin to ground like in the image below (red wire for ground, i know, i know) and your fuel pump runs with the key on then your problem is either your FI brain or the harness connecting the brain to the relay board.

The FI brains rarely die but it does happen ...

Yes indeed. that's what it does. So on that pin III of the relay board, it's cool for there to be 12V with key on then? Only reason I ask is because in the troubleshooting doc mentioned in the original post, they mention power only at 16 and 24 of the ECU. With 12V at III on the relay I then of course have 12V at 19 as well on that ECU connector. Just checking.

Dave

No! That's a ground, if that had 12V hooking it straight up to the chassis would let a lot of smoke out.

It is the ground for the fuel pump relay, which is normally controlled by the FI brain.

Exactly..... this is why I posted. Did not make sense to me but I have 12V at III on the 4 post on relay board with the key on. So looking at the schematic, III connects to 86 on the Fuel Pump relay. That's it..... so my four wire harness from those roman numbered plug that goes to the ECU is unplugged as right now 12V on III then pin 19 of the ECU cannot be good. For power to be on 86 and III it has to be either my connections under the relay board are making contact with maybe (I), which has 12V and powers the ECU OR pin 30 or 85 on the actual fuel pump relay are somehow making it's way to 86 via the relay which should not be the case....I think Funny thing is they test out on the headlights.

Im baffled but will pull the relay board tomorrow and check that out, if good I'm going to apply 12V to 30 with the relay only (in my hand) and see if power if somehow getting to 86, if not apply 12V to 85 and same test. RATS!!

Scratch that, looks like III is connected to 86, not 85 ...

Holy crap, i never noticed this, but look at 85/86 on the earlier relay boards for that same relay!

So it looks like for your car the trigger (12V) is on III and the ground is on I which is flipped from what i had on my car ('70) when i took the image of my relay board.

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?

The 12v power leading to pin III is actually on the other side of the fuel pump relay. It is not really a power circuit there it is a ground circuit that is not yet grounded
You can read it as 12v because the meter you are using draws so little current. The coil in the relay I just measured has 0.1 ohms of resistance, which when measured with very low current will make almost no change in your voltage reading. When the harness is plugged in to the relay board and the key turned on the control unit is supposed to switch the circuit to a ground and engage the relay. If you back probed pin III with the harness connected and watched the voltage it would drop to 0 when the control unit grounded it.

If you were to take a test light and with the key on and the harness unplugged and one side of your test light hooked to a ground and then touched pin III the would not light up or possibly barely glow. Not enough current can pass from terminal 85 through the relay coil to terminal 86 to light up a light. It only passes enough current to operate the coil in the relay.

Jim

Just as a follow-up I unplugged the FI harness from the relay board and measured the voltage at pin I and pin III with the key on. I measured 12.44 volts at both I and III
With the FI harness plugged in the fuel pump runs briefly when I turn the key on.

I had two bad relays on the relay board and had to swap the good ones into the right spots.

Jim

It appears to be a typo on 2nd drawing as the PCB layout is identical. I'm going by the schematic below which shows the 86 pin next to the 87 pin.

Click to view attachment

Excellent information guys, thank you. I'm just scared because the original ECU that came with the car was beat to begin with but when I tried it I never got the ground from 19 to blip III and cause the 2 seconds of Fuel Pump. Got another ECU from a source out here in the bay area and the same dang thing happened. I was beginning to think that two ECU's with the same issue was more than a coincidence. Again, testing 22 steps off Jeff's Bowlsby's web site. Each time telling me I had an ECU issue. Well my source has shipped me three more ECU's to try. I did not want to be blowing these suckers up somehow and because I was seeing that 12V at III with key on I was thinking down the harness from that III to 19 on the ECU and perhaps smoking something.

Yeah with respect to that spec being whacked the Fuel Pump Relay. I saw that and was just more confused. I'm going to also call my source today as they have a running 914 in the house and just confirm that 12V at III. Will feel so much better than plugging in these three ECU's I just got in yesterday.

As mentioned before the 12V on III is expected since you're measuring the voltage on on side of a coil where the other side is attached to 12V.

So the circuit you're measuring is this:

PIN III-----------------COIL-----------------12V

If you want to test this out, just remove the coil and measure pin III. You should get zero volts.

How did you test this? Did you ground pin III?

By saying "AKA fuel pump", you mean the fuel pump is running, correct?

Yes.... Aka was a poor way of saying ground from 19 to III to flip the fuel pump relay to send power out 78 and up to pin 13 of the cabin harness which are the wires going directly to the fuel pump.

Third ECU..... it all worked. Now I'm headed in a new direction. Doesen't start.... almost tries but no cigar. Will mess with the distributor in the morning and check everything out. Getting there.

Thanks again everyone.

Dave