944 S2 Stalling/Hesitating when wet

[cda951]

I pulled the O2 sensor, and I decided it was worth replacing after seeing it too. There was definitely some peeling electrical tape from at least two spots on the wiring. Now, I'm just waiting for some rain to really test it.

I _did_ go for a drive-thru car wash, which has definitely triggered this before. There were no issues. There's no rain in the forecast for at least the next week, and I've already turned off the hoses outside for winter, so I was impatient. I'm hesitant to call victory yet, but I'm cautiously optimistic.
-N

Hi Neil,

Late to this thread, but I hope you solved the issue! The fuel pump and the oxygen sensor heater power wire share the same circuit/fuse (#34), so if the deteriorated O2 sensor wiring was the issue, the only way it might affect both the fuel pump control circuit (85b) AND the main fuel pump circuit (87b) is perhaps moisture inside the oxygen sensor wiring harness is somehow causing the heater wire to momentarily short to either the oxygen sensor signal wire and/or shield ground, which would not draw current enough to blow the 15-amp fuse, but this maybe activates some sort of overcurrent protection circuitry within the DME (?). I'm trying to envision how the 85b ground signal from the DME to the fuel pump relay coil would intermittently drop out . . . .

If it were ONLY the main fuel pump power/87b dropping out, then I'd be suspecting an intermittent open or excessive voltage drop in the fuel pump power circuit, but that would likely happen wet or dry.

Let us know what you find.

[neilschelly]

Yes, it is resolved, and yes, it was the O2 sensor wiring. Sorry I forgot to update this thread. Anyway, it took many weeks of waiting for a proper rain storm to drive through, but I went for a 2-hour drive through high speed, low speed, stops, restarts, etc, and I had no issues. There wasn't a single hiccup in the whole drive.

To be clear, what I found when I was looking at the wiring diagram was that grounding out at the O2 sensor could cause the ECU's fuel pump signal to get grounded out. And that tracks with what I saw on the F9 DME relay lights. The actual DME signal to the relay is what was stopping, and the relay was stopping the main power circuit to the fuel pump because of that.

-N