1987 Carrera 3.2 Completely Dead On Key Start

[SpiderCider]

Alright folks, here's a head scratcher for all of you. My 1987 3.2 has sprouted some electrical gremlins out of no where. All the auxiliaries work and when I turn the ignition on all the dummy lights and gauges come to life. But as soon as I turn the key to the start position, everything dies. No lights, no power locks, nothing. If I disconnect and reconnect the battery, or if I let the car sit over night, everything comes back to life. Sometimes the car starts without any issue. Last night it didn't and is now sitting in a parking lot. My guess is that there is a bad relay somewhere and it must be close to the battery as it shuts down everything in the car. Has anyone ever had something similar happen or any ideas on what might be the cause? Is there a relay that I should go after?

[Green6]

First thing I would check is to make sure the battery terminals are clean and snug. Also check the main chassis ground near the battery. When you disconnect the battery are you pulling the negative terminal off, or do you have a disconnect switch? If you have a switch check the connections to that also.

[SpiderCider]

Green, the battery is good and connections are solid. I've been removing the ground cable each time.

[SpyderMike]

The thing I did not like about my car (a 1985) was the fact that most of the power was routed through the ignition switch and then was branched off from there to the fuse block where different taps from the ignition switch powered buses on the block. All that power going through the switch.

Here is a post I made about that switch:

understanding the ignition switch

Now see that in the START position, both buses 15 and 50 are affected. 50 just powers the start circuit, but 15 is used for gauges and the like and could give the symptomos that you are seeing. It could be your ignition switch electrical side.

Do you have to wait overnight for the recovery?

Mike

[SpiderCider]

The plot thickens. I went to try and start the car tonight. The cabin lights would come on, but I couldn't even get the gauges and dummy lights to come on. So I hooked up the jumper cables and suddenly power! I tried to start it got about a half crank before everything died again. Seems like my battery is dead. I'll let it sit on the trickle charger for a day or two and then see if I can get the car started. I find it odd that the car wouldn't start with jumper cables hooked up...

[Driven97]

If you're SURE the battery and grounds are ok, any chance of an old aftermarket alarm / kill switch lurking in the car somewhere?

[cabmandone]

Originally Posted by SpiderCider

The plot thickens. I went to try and start the car tonight. The cabin lights would come on, but I couldn't even get the gauges and dummy lights to come on. So I hooked up the jumper cables and suddenly power! I tried to start it got about a half crank before everything died again. Seems like my battery is dead. I'll let it sit on the trickle charger for a day or two and then see if I can get the car started. I find it odd that the car wouldn't start with jumper cables hooked up...

A dead battery normally won't fire off unless given a chance to build up even with jumpers on. I'd question if you don't have a dead short in your battery. How old is it?

BTW, have you checked all ground locations and cleaned? You have 1 up by the battery, 1 from the trans to chassis under the car should fasten on the passenger side floorboard under the car and then the grounds to the intake runner. I'd make sure you check them all. I've read posts where the ground cable from the trans to chassis got frayed and caused issues.

[al lkosmal]

Check the ground strap between the trans and chassis....under the car. Remove it and clean all of the connections. A way to check is this is you problem is to hook your jumper cables together to form a long jumper and hook one end to the chassis ground point the battery is hooked to and the other clipped to the tranny case by the starter...I.E you are supplying a direct path to ground. If your 911 starts right up...replace the crusty ground strap.

regards,
al

[porschenut]

Your battery is not dead. If it were, how would lights and accessories work? Try a new DME relay.

[cabmandone]

Originally Posted by porschenut

Your battery is not dead. If it were, how would lights and accessories work? Try a new DME relay.

I don't see how changing the relay that actuates the fuel pump is going to fix the problem. His car isn't cranking occasionally. The DME relay has nothing to do with the car cranking, now firing is a whole different thing. You can crank your car all day long without a DME relay installed, it just will not fire.

Ever see a battery that you could turn your headlights on with yet couldn't crank the car? I have.

[ischmitz]

sometimes a simple Digital Multimeter helps.....they can be had for less than 10$ at your FLAPS or on evil bay.

Measure the battery voltage by touching both lead poles while an assistant cranks. If the voltage drops to below 8V you know what's going on. The starter has some pretty nasty power demands and a battery that might appear perfectly fine when powering just some lights might be brought to its knees when the starter wants to draw 50 Amps or more.

Further, when you say you hooked up jumper cables you need to let us know exactly what you connected where. Let's assume you had another battery/car supply +12V to the battery of your 911 while it was installed in the car. If with that scenario you still had issues starting you might have an issue from the battery to the rest of the car and the starter in particular. As others said there is a ground wire from the battery directly to the chassis. All other consumers (starter, lights, etc.) itself have one wire going to chassis for GND. And the engine/transmission has a braided line (ground strap that ensures good electrical connection to the chassis. The positive big wire goes directly from the battery to the starter relay and on to the alternator. Other lines go to the fuse panel.

Ingo

[wwest]

Very rarely I have encountered a broken bus inside the battery...

Battery works fine for light loads but DEAD for starter level loads.

Wiggle the post, internal connection goes bad? Good?

[shbop]

I know you said you checked the grounds, but double check the chassis side of the battery ground strap. Just went through a similar deal. Had the exact symptoms you describe. I'd double check the ground strap from the trans to the chassis as well.

[porschenut]

Originally Posted by cabmando

Ever see a battery that you could turn your headlights on with yet couldn't crank the car? I have.

I have too, but that just indicates a weak battery, not a dead one. Important distinction.

[rick-l]

I had two sears diehard batteries that died hard like this. Turn the key and it was lights out, dead, walk home.

[SpiderCider]

After letting the battery sit all night on the trickle charger, the car started right away. I checked the voltage while running and had 13.8V at the battery. All the dummy lights came on too before cranking. So the alternator seems to be working fine. I'll check the ground straps in the daylight. But now my guess would be a short somewhere that is draining the battery when the car is parked. Thank you all for the help so far!!

[cabmandone]

Originally Posted by porschenut

I have too, but that just indicates a weak battery, not a dead one. Important distinction.

As I understand, it can also indicate a dead cell. There's enough voltage to turn on lights but not enough amperage under load to crank the car. That's why when you bring the battery to a car parts place they put it under a "load test" because the voltage shows good but the amperage is too low.

[cabmandone]

Originally Posted by SpiderCider

After letting the battery sit all night on the trickle charger, the car started right away. I checked the voltage while running and had 13.8V at the battery. All the dummy lights came on too before cranking. So the alternator seems to be working fine. I'll check the ground straps in the daylight. But now my guess would be a short somewhere that is draining the battery when the car is parked. Thank you all for the help so far!!

If you do some searching here, I know I've seen a thread on running down a battery draw. You use a amp probe to see what amperage is being drawn from the battery with the key off. IIRC there should be a very slight draw from the clock and the ECM but I don't recall the exact figures. Maybe Ingo can chime in here.

[ischmitz]

Check convenience lights (trunk, glovebox) and any car stereo or amp that doesn't turn off. Finally a leaking alternator diode can cause that, too even if the system charges fine

[ganun]

+1 what ischmitz PLUS ......On my 87, after experiencing a dead battery if the car sat for a week or two, by luck, in a dark and quiet garage not only did I see a faint spark while connecting the battery terminal but heard the faint click of a relay.
A relay hidden behind the drivers side trunk hinge was clicking when the battery was connected.
It was the Fensterheber Relay that stays on. I just pulled it since its about 100 bucks and it's for convenience.