Kandlhoft

Hello Rennlisters,

I have an 85 32V project 928 I've been trying to diagnose a no start issue. I'm checking the voltage at the fuel pump, which when the battery is connected, starts out at 2 volts and over the span of five minutes works it way up to 9.5V and hovers at that voltage. The fuel pump relay on the CE panel was really well wedged into the socket, but once removed there was little corrosion on the relay pins. I also ensured the fuel pump fuse looked good and didn't have corrosion either. I cleaned the contacts on the CE panel with Deoxit, jumped pins 30 and 87 on the panel and tested voltage... with the battery hooked up, same slow climbing voltage deal. The battery at its terminals measures 13V. Any idea of what may be going on?

Here is a short 1 min youtube I made showing the issue -
Thanks!

GregBBRD

1. Replace that original battery ground strap with a new one from Porsche. (Factory strap, only....no one's idea of a "better/cheaper" strap.
The original ground straps are source of many issues.
(We keep multiples of these in stock, at all times.)

2. If #1 doesn't fix your problem, leave the red wire from your voltmeter hooked up to the red wire that goes to the pump.
Remove the black wire from your voltmeter from the black wire to the pump and hook it up directly to the battery.

This will tell you if you have a funky ground on the black wire to the pump, or if the problem is from the power source.

Kandlhoft

Thanks Greg! I just tested the black ground directly against battery and it still has the climbing voltage?

Kandlhoft

I removed the plastic sheathing from the grounding strap and it looks good! Not really any corrosion.

GregBBRD

And it's a soldered ground strap.
That's not the problem.

GregBBRD

OK.

I'm assuming that you have the fuel pump relay jumpered (30 to 87) while doing this?

If so, go to the relay/fuse board and see what the voltage is on the connector that plugs into the board and goes to the pump.

Kandlhoft

Correct, I had 87 and 30 jumped on the CE board for the fuel pump relay. Between 87 and 30 I am getting a consistent 10.5 Volts.

Alan

I'm confused - is the fuel pump connected? or removed when doing this? What is the voltage on your jumper between 30/87 on the fuel pump relay (wrt ground on the console power outlet)? same as fuel pump reading? [was this the consistent 10.5V?]
if the pump was removed/disconnected repeat with it connected. If not try directly powering the fuel pump from the battery (with a fuse) - will it run?

Test the fuse electrically (ohms) - try replacing it too, and evaluate again after testing.

With ignition on measure the voltage from the -ve battery lug to the ground point that the battery ground strap attaches to (the bolt/wing-bolt) - do this while flexing the battery strap by hand (use the 2V scale for this measurement).
With jumper in place measure the voltage from the -ve battery lug to the ground of the fuel pump (case)

Overall - I'd expect it is most likely an issue with the fuse first - it is situated after the relay - or a ground issue somewhere (especially if the pump is still connected when you saw this).

Alan

Kandlhoft

I found the issue! Bad ground wire on the connector for the fuel pump. The protective plastic boot was hardened solid. I ended up cutting it off. Thanks for all the help and suggestions! Voltage tests normal now.

SwayBar

Nice find!