964 Won't Start After Rain

[BlueSideUp]

Hello, I am trying to help a friend with her 964 C4. I have a lot of experience with newer Volkswagens and some experience with older 911s (valve adjustments, etc.).

Basically whenever it rains this C4 will not start. It turns over just fine and does not smell like fuel even after repeated attempts to start. Every once in a while the car will fire a cylinder or two but that's it. The car did just start to have smoke out of the exhaust and fire a cylinder consistently after the fifth time trying to start.

Once the car dries out it runs perfectly and never has any problems. From searching the archives it seems that the DME relay has been known to cause problems in these cars. Apparently this is located in the front fuse panel, where is the front fuse panel located? I would like to check it for any water.

The engine compartment looks fairly dry, the relay box on the driver's side of the compartment is completely dry inside and the relays are seated.

My friend says the car has done this for a long time and her mechanic said he can't diagnose the problem unless he can test while it is malfunctioning.

Thank you so much for your help.

[colo964]

The relay guide should be on the sticker on the fuse box. It should say "DME Relais" or some such eurotalk on it. Sorry, I'm 100 miles away from my car so can't tell you which one, exactly.

I've had trouble starting in the rain when my rotors and caps were too worn. Look at the distributor to look for burns, corrosion, and general wear. They are pretty cheap and pretty easy to change out.

Does it happen after it's been driven? I ask, because I had a problem with my C2 running at all after driving in the rain. It turned out that the O2 sensor was shorting out. Ran fine after it dried out. Just another data point.

-CKKrause

[BlueSideUp]

Excellent information. The car will not start at all after it rains. Forgive me for not having much knowledge of the car, this is the first time I've been around a 964. Where is the fuse panel?

Any ideas where the connector is for the oxygen sensor? If I disconnect a shorting oxygen sensor it should be able to start.

I also thought about checking the interior for any wetness, another thread described a problem with the DME computer being mounted under the passenger seat. Apparently the door seal was leaking and caused the computer to get wet.

[Tom W]

The DME relay is in the fuse box in the front trunk under the carpet (upper right side). The ECU (compuetr) is under the drivers seat. It would have to get pretty flooded to get wet, but the sound dampening matterial holds a ton of water when it does get wet.

[BlueSideUp]

OK I think the o2 connectors are in the relay panel on the driver's side of the engine compartment. If I remember correctly there are two connectors and two relays, any ideas which one is the oxygen sensor?

Thanks so much for your help!

[colo964]

The place an O2 sensor would most likely short is in your left rear wheel well. Sometimes the wire insulation wears out (e.g. rubbing on the tire) and when the wires get wet, they short, causing a poor start/low power situation. If that is the problem, you can unplug the sensor (remove the fan blower on the left side of the intake manifold to access the plug) and operate the car...just remember to get a working sensor come smog check time.

[BlueSideUp]

OK I am gone on a trip and she is trying to start the car again. This might be kind of difficult but can you describe in easy terms how to access the plug for the sensor? I know there are the two plugs in the relay box but I gather the o2 plug is somewhere further forward along the sidewall.

Hopefully I can describe the plug position before the starter gets burned out

[Tom W]

The easiest way to guarantee the right plug is to trace the wire from the sensor in the Catalytic converter. You pull the wheel and may want to remove the fender liner. I don't have the Workshop manuals handy (at work) and the PET isn't clear on routing.

[AFJuvat]

Make sure that the distributor and\or coils aren't getting wet. Seems to happen to some 964\993. Water leaks through the tail and soaks teh dizzy.

AFJuvat