got stranded .... |
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got stranded .... |
dax1969 |
Apr 17 2023, 09:13 AM
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#1
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Member Group: Members Posts: 366 Joined: 10-March 14 From: belgium Member No.: 17,103 Region Association: None |
Hi guys,
Got stranded yesterday with my 1974 2.0 fi... no buzz fm the fuel pump. Saturday the car started and ran great, only thing I did to the car that day is that I took my steering wheel off as it was a few teeth off center. Used a impact gun to remove and install the big nut (no idea if this has something to do with my issue). Perhaps I had to be more gentle ... Before I left on sunday morning I turned the key and heard no buzz fm the fuel pump... tried again and there was the buzz and the car started right up. Went to fill up the car and no issues with starting. After a 50 km drive I parked the car and when I came back again no start/no buzz fm the fuel pump. Started switching the relays, even with the ones fm the headlights... no buzz/no start. Switched fuses on the relay board (that's why you see the white in the position of the blue and vice versa)... still nothing. Called roadassistance and luckily an older gentlemen showed up. He took his voltmeter and said he could get the car started if he jumpered the relays - see picture. The car indeed started right up and I headed the 50 km back home with no issue. Disconnected the jumper ofcourse as the pump otherwise kept working. So where to start fm here... I have the file "porsche 914 fuel pump troubleshooting" but did not go through yet. I just keep wondering what could cause my issue. The questions I have are the following : 1. Can the removal/reinstalling of the steeringwheel cause this issue (perhaps the connection of the switch came loose ? Pinched a wire so no ground ? 2. Ignition switch was replaced about a year ago (Porsche one, not chinese crap). If an ignition switch fails, does the car crank or nothing at all ? Trying to figure out if I have a switch failure. 3. My fuel pump has a slight "humm" for a while (assumed it was resonance with the bottom plate (fuel pump is located near the rack) but can a fuel pump go bad "half" ? I mean can she fail on giving the familiar buzz at start up but still run when relays are jumpered ? 4. Relay board itself was replaced a year ago with a rebuild one fm Bruce Stone Some advice I received on facebook 1. splitting/widening the relay pins (did this in the past but perhaps have to do it again) - fyi ordered new relays anyway 2. bad CHT sensor ? But once the car starts with the jumpered relays, the car runs fine. Overruled by other members in the meantime Any suggestions are welcome... thks Krgds Dax |
Spoke |
Apr 17 2023, 11:36 AM
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#2
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Jerry Group: Members Posts: 6,992 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
Here's another schematic view of the relay board. Your guy jumped relay K74 (ECU power supply) and K75 relay (Fuel pump). So 2 relays were jumped. K74 provides 12V power to the ECU on Pin 1 of the FI power connector also power to K75 on pin 85.
Follow K74 pin 85 back to the connector to cabin and you see it connects to pin 8 which is from the ignition switch. w/o 12V on pin 8, the power supply relay doesn't work and neither will the fuel pump. Since your car didn't start up, you don't know if the power supply relay didn't get power from the ignition switch, or it's contacts were not making good connections, or if just the fuel pump relay didn't pull in or has bad contacts. When the problem happens the only audible feedback you get is the fuel pump not running. You can't hear the ECU running or not. Since your guy shorted 2 relays, you don't know which relay was causing the issue. Likely only one relay caused the issue. You can try bending the relay leads out a bit but if the issue is in the wiring or ignition switch, you still have an issue. Until you solve the issue, you should carry those little jumpers with you and your voltmeter. If it happens again, check for voltage from the ignition switch by measuring from the 8A fuse (which also is connected to the cabin connector pin 8) to chassis. If you have voltage on the 8A fuse, then try jumping just one of the relays at a time to see which one is not functioning. You may also want to reseat the cabin connector (make sure not to get off by one pin) and the FI power connector. About the impact tool on the steering column, it may not have done anything or it did. Large vibrations anywhere near wiring/connectors/fuses is not good. Attached thumbnail(s) |
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