I've done searches, but found nothing for this head scratcher.

Turning the key to the start position kills all voltage from the battery to the cockpit and starter. All lights go out and the starter never blips. Disconnecting and reconnecting negative battery lead restores voltage, but problem repeats when the key is again turned to start.

Checked so far:

- Battery condition fine.
- Engine turns by hand (not seized).
- Negative grounds good.
- Alarm system seems to be working as it should, e.g., Security light, alarm function, and key disable all OK.
- Pulled fuse on alarm.
- Disconnected alarm sub-harness.
- Alarm relay 2 OK (tested and also jumpered).
- No codes (as you would expect).
- Battery never connected in reversed polarity.
- Was running fine before car sat in storage two months.
- All fuses and fusable links OK.
- ECU connections visually OK.

Any ideas as to what would cause this immediate loss of connection to the battery when the key was turned to start, and then be reconnected when the negative lead is removed and replaced?

Things I can try next:

- Alarm system troubleshooting from FSM.
- ECU troubleshooting.
- Others?

Thanks in advance!

Mike
'87 300ZX, NA, Manual

 

Have you checked your starter yet? The solenoid could be fired by the sounds of it.

 

Thanks, Blue, good thinking. I was probably too fixated on the alarm system as the culprit.

Back to basics! I whacked on the starter/solenoid to no avail. It still may be the issue, so I'll troubleshoot it further. Thanks for the quick input.

The strange thing is, after the above whacking, I now lose power as soon as the key is turned only to on, or any light switch is thrown. This may be a function of draining the battery with my testing (now ~12.3V), or maybe it's been the battery all along.

Maybe it's a marginal cell and the battery can indicate a full charge, just not deliver a high current jolt. If so, I've wasted everyone's time. I'll try another battery and report.

Mike
'87 300ZX, NA, Manual

 

lol No harm done. but it wouldn't hurt to take your starter and your battery, possibly your alternator down to an auto parts store and have them tested to make sure their all working correctly.

 

Thanks. I tried a known good battery and I'm getting the same symptoms. My first battery checked OK at AutoZone.

On a hunch, I checked and received strong continuity between the disconnected positive and negative battery cables. As Blue thought, this may indicate a hard short in the starter (or alternator).

I'll drop and test the starter per the FSM tomorrow. The alternator is pretty new and was working fine, but I won't rule that out, and test as necessary.

Any thoughts on the continuity/short suspicions?

Thanks in advance.

Mike
'87 300ZX, NA, Manual

 

Only thing I can think of, is the starter might be seized up, or the solenoid is shorting out. or even both!

Good luck on your electrical gremlin hunt!

 

Thanks for your help and encouragement. It may take a little while, but I'll post a follow-up/problem resolved post. I've lurked the various Z31 forums over the years, and have benefitted from the knowledgeable contributors. I spend most of my time on Rennlist, bimmerforums, and ford-trucks.com, and recognize the value of the "issue resolved" posts. I try to make sure I follow-up wherever I visit.

Thanks again.

Mike
'87 300ZX, NA, Manual

 

Found two possible issues, and when they were resolved, the car cranks great with no voltage shutdown issues.

1. The starter itself. When bench tested, it seemed to crank great. Brushes, bearings, and all DVM checks per the FSM checked OK. I reassembled it and had it checked by AdvanceAuto and AutoZone. Both checked OK, however, it drew 100A which is at the upper limit of the spec. I reinstalled the starter, and when I connected it directly to the battery and manually jumped the solenoid, it cranked slowly, but (of course) did not kill the voltage as I described in my original post. I ordered a new starter, and suspect that this one was just tired or had an internal mechanical issue creating the excessive current draw.

2. Voltage drop. When I installed the new starter and connected it to the car's wiring, the voltage shutdown issue still existed. When the car's wiring was bypassed as in #1 above, the starter cranked great with no shutdown. In my original post, I stated that the grounds were good. However, in my lazy approach to jump to a solution, I only checked continuity, not voltage under load. I went through everything checking for voltage drops on the positive, negative, and key signal to solenoid paths. The ignition switch, clutch switch, connectors, fuses, positive harness, and relays checked OK. The negative body and transmission ground showed a drop of over a Volt. Not much you might think, but a smoking gun, nonetheless. I replaced the negative cables with new, and it cranks great through the car's wiring with no shutdown.

I guess the moral is, don't try to jump to a solution, and use proper troubleshooting procedures. Oh also, as they say in another one of my favorite forums... Check your f'ing grounds.

Follow this link for a good discussion on voltage drops, and check out the site as it's a pretty good general automotive repair library.

http://www.aa1car.com/library/voltage_drop_testing.htm

I still don't know what system would shut the voltage down when experiencing the above two issues, only to be reset by disconnecting and reconnecting the power to the battery. Oh well, it's fixed... and now on to another new thread about my fuel pump circuit electrical woes (to be posted shortly).

Thanks for your help.

Mike
'87 300ZX, NA, Manual