1972 1.7 - Fuel pump not starting when key is turned, Problem with fuel pump Options

[itsmagic]

My 1972 1.7 914 recently decided to not start. I quickly noticed that the fuel pump is not running briefly like it should after the ignition key is turned. I verified that the relays on the relay board (Master, Fuel Pump, Blower) are all good by trying them on the headlight motors. I then verified that the two fuses on the relay board are good. Next, I popped the cap on the fuel pump relay and pressed it... the fuel pump runs when I do this. (The car will then start and run for a few seconds if I start it). Sooooo, I am at a loss... The fuel pump is fine, relay board is fine, relays are fine... what could be causing the fuel pump to not activate? Thank you for any advice. Wayne

[Chris Pincetich]

I AM GOING THROUGH THE EXACT SAME THING as Wayne, who started this thread. (IMG:style_emoticons/default/sad.gif)

I thought it was a bad relay board, and have tried several other boards without finding my fix (Thanks Bruce for sending them!).

I just learned about and tried the exposed relay test, and it did work, which means my relay board should be fine. With the relay innards exposed, I turned the key in the ignition to ON then pressed the relay and the fuel pump started running. I have also cleaned all the relay connections on the board, cleaned the relays, tried several working relays, and bending the relay prongs for a tighter fit. Still no power to the fuel pump! (IMG:style_emoticons/default/dry.gif)

Does this mean it's time to swap out and try a new ECU brain??

I've been driving the 914 for over a week with the fuel pump wired directly to the battery. I have to unhook the battery every time I park.

Is using a modified relay, one that is "always on," a bad idea for a temporary fix??

Seems like it would be the same thing as I have now (pump always on when car is going) but would mean I don't have to unhook the battery every time (and I could use the OEM pump electrical connection/wiring).

Thanks in advance for more advice and tips (IMG:style_emoticons/default/beerchug.gif)

[jcd914]

I thought it was a bad relay board, and have tried several other boards without finding my fix (Thanks Bruce for sending them!).
I just learned about and tried the exposed relay test, and it did work, which means my relay board should be fine. With the relay innards exposed, I turned the key in the ignition to ON then pressed the relay and the fuel pump started running.

The "exposed relay test" does not mean the relay board is good, it only verifies the power circuit to the relay and power circuit out to the fuel pump are good. But considering you have tried a number of relay boards, yours it probably not the cause.

Does this mean it's time to swap out and try a new ECU brain??

It means it is time to test and determine if the ECU is trying to operate the fuel pump relay.
Using the diagram and info Tom posted you need to verify the fuel pump relay get power to the 85 terminal and then check to see if the ECU grounds terminal 86. If you don't have those at the relay socket then move and test at the next connection in the circuit.

I've been driving the 914 for over a week with the fuel pump wired directly to the battery. I have to unhook the battery every time I park.

Bad idea. Fuel pumps are controlled by relays or modules for safety. In an accident or if you had a fuel line burst you could have trouble getting to the battery to disconnect it. And if you had a fuel leak, that little spark you get at the battery when you disconnect it, could be the spark the sets your car on fire.

Is using a modified relay, one that is "always on," a bad idea for a temporary fix??
Seems like it would be the same thing as I have now (pump always on when car is going) but would mean I don't have to unhook the battery every time (and I could use the OEM pump electrical connection/wiring).

Yes, bad idea. It would be very similar to what you have now, which is why it is a bad idea.

I worked with a mechanic that constantly drill in to me "Test, don't guess". Diagnose the fault in the circuit and then you can determine the best fix. Tom's info should help.

As was said, ECU's don't fail often but they do fail but IMHO the FI harness is probably a more likely culprit.

Jim