gwertzman

My 92 911 C4 just developed a vexing electrical problem. It first surfaced when I returned to my car after a brief errand to find the car's electrical system completely dead -- no interior lights, no ignition, no nothing. Turning the key did nothing. I assumed it wasn't the battery -- i'd never heard of batteries falling utterly -- but i did open the hood to see if maybe the connector had come off the battery. Nope, the connector was still there. Mystified I returned to the cabin, and idly turned the key to the on position -- and after a few seconds was rewarded by the car returning to life. Dashboard lights lit up, the fan turned on, and I was able to start the car and drive away.

A day or so later, while driving home, the radio unexpectedly cut out for a few seconds then came back on. I was curious if this was related to the power problem I'd experiencd earlier -- and sure enough, when i got home, after i turned off the ignition, the car was once again dead. Not even power to lock the door. Since I was home, i was able to test the battery with a multimeter -- sure enough, the battery was fine. Once again, i turned the key to "on" and after a few seconds the car came back to life.

Finally, last night, it happened again -- only this time I was out in a dodgy part of town and regretted not being able to lock the doors (is there any workaround to that power lock system?) -- and more importnatly, this time turning the key to "on" for a few seconds did nothing. The car seemed completely dead. I opened the hood and fiddled with the cables on the battery, but they were all solidly attached. Thinking I'd finally need to call a tow truck, I returned to the cab and tried the key again and again and eventually after a few tries the car came to life. I was able to drive home and upon reaching home, after turning off the key the car still had power so I could lock the door.

Now i'm afraid to drive it -- not sure whether the next time i'll truly be stuck somewhere. any ideas on what this might possible be? Is this a known porsche affliction? Or do I possibly have some strange loose connection somewhere? Very interested in any ideas or suggestions on how i might troubleshoot. I'm not sure if the key has anything to do with it or not -- i'm thinking it's a coincidence that i happen to hav the key in the "on" position when a loose connection or whatever it is happens to reconnect. The strange thing about a loose connection theory, however, is that nothing in the car is moving when it's parked that might account for a loose connection reconnecting.

Thanks!!

darth

1st thing I'd do is clean the battery posts and connectors with sandpaper or equivalent, and carry around a voltmeter so that when/if it happens again measure the battery voltage while it is in this dead state at the battery. You may have an intermitten connection in one of the battery cells where one of the battery plates in one of the cells becomes physically/electrically disconnect from the other cells resulting in zero voltage at the battery terminal.

Hope this helps
Bill
90C2

Marc Shaw

Try changing the DEM relay.

Marc

J.PELLEGRINO

The dme relay would not cause problem...I would check the ground connections near the battery as well as the one between the gearbox and the chassis..I would also carefully inspect the battery cables, I have seen the cables themselves, under the insulation get very corroded and although the connections on the battery is clean, the cable will not pass any noticeable current...
Just a thought, Jerry

H964

well i had a similar problem on my old 964, it was the ignition switch.
to test it, start the car and play with the key see if it dies.

DaveK

I've also had problems with the ignition switch - I used to be able to get out of my car, lock the doors and then noticed all my ignition lights were on.

I don't know if this could prevent you from locking the doors though?

Porsche_Red

Sounds like the ignition switch to me and it would tie in with your radio issue - could be just bad connections or internals on the lock. Are US cars different - on mine I can lock the doors with the ignition key (immoboliser works but alarm doesn't engage).

J.PELLEGRINO

I am not sure that would effect the door locks with the car off and door shut....

gwertzman

thanks for the suggestions. I'm thinking it's not the keyswitch since when it's dead it's truly dead - interior lights don't work, battery forgets its presets, etc. Could a bad switch account for all those issue?

I'll definitely look into the battery suggestions.

Also, regarding the door locks, my copy of the "enthusiast's companion" seems to indicate that the doors can still lock with no power -- but that wasn't my experience. I could Unlock the door, no problem, but not lock it -- it felt like when i turn the key i'm just hitting a switch that triggers the central locking feature. am i doing something wrong? should i be twisting harder?

darth

Did you try locking the door by using the **** on the inside of the door? The door has to be shut in order to lock the door using the ****.

Hope this helps
Bill
90C2

gwertzman

So in case anyone is interested, it turns out the solution was to replace the grounding strap. Using my multimeter, I found a suspicious voltage gap between the ground terminal of the battery and the chassis. Sure enough, the grounding strap, once removed, showed significant resistance. I'm guessing corrision inside. Now that it's been replaced evreything is fixed -- and my interior lights are brighter than ever!

As for the locking - I understand that the **** works from the inside, but how does that help you lock the car when leaving it if the battery ever should die?

DaveK

I've seen a few posts about the grounding strap before.

I don't have any electrical problems (actually - I do have one, but I don't think that's the cause) - but I may stick my multimeter on mine one day just to see if it's OK.

J.PELLEGRINO

I believe the lock cylinder mechanically unlocks the door so it can be opened with the battery dead, but the lock function is handles electrically via a micro switch on the lock cylinder.

Jerry

Edgy01

Sometimes it's the clock. If it's acting up it will drain the battery. Worth checking.

Johnny-Cat

This is a good lesson, I think I will replace my ground strap even though my car is not having any symptoms like that. Good preventative maintenance there. 1991 964 C2