Non start issue- think I have found the problem!
 

New Battery
New electrical section to starter key switch
New (refurb) starter motor

old threads :http://forums.pelicanparts.com/porsche-911-technical-forum/596120-930-non-start-issue-continued.html


When cold alternator charges battery
Volts change from 12.8 volts at idle to 13.5volts

After running engine up to temps (80c) I tried to load up the fuse bank and electrical system with headlamps, turn signals and then finally A/C.
Ran all for 5 mins or so then stopped car
Let car sit for 1/2 hr

Restarted car and volts on batt terminal 12.25v dropping to 12.20v after 5 mins at idle.
With wife reving car to costant 2Krpm then 3krpm no change in voltage

When I then load up the car with headlamps and A/C volts on batt drop to 11.5v

All new fuses intact on strip.

Is there a seperate voltage regulator on these alternators? '87 930

Any other areas I can check for break in charging system?

I will let car cool and retry to see if I get charging when cold again!

I will also then try with my old battery

I hope I have it as this has been bugging the car for 6 months and I have no confidence driving it anywhere without fear of tow home!

Extra info/tests appreciated

Had an intermittent no-crank in my newly purchased '85 Carrera. Parked on slopes and hills for awhile! The intermittent cranking became somewhat permanent at one point, lending the head scratching to actual hair pulling!

So, ordered up a rebuilt starter from our hosts, and a new tranny/body ground. The ground I took out had mostly a greenish hue mixed into the fine copper threads. Before I installed the ground, I bench-tested the starter and of course, it worked great. Boy, was I excited! I then installed the ground strap, and the old starter, nothing. I have a car lift in our machine shed, a large 30x60 farm building, so working on this car is not bad. But, my excitement was somewhat dimmed!

Well, after more head scratching, I did what you did, and checked the battery voltage. 12.5 volts thru the red cable attached to the starter, 12.5 volts at the battery terminals. Hmmmm, why no crank? The starter solenoid at this voltage, activates, I can hear the 'clack' sound, small relays 'click'! The fuel pump was humming, but no start. I finally put the battery charger on the battery for an hour.

When I turned the key to the 'run' position, the HVAC system came to life! I'm liking this turning point! Must have had the system on and didn't even know it. The final twist of the key, and the engine roared to life! It's been a couple days, and I still leave the HVAC system on, and if the fans come on before crank, I feel the car will start, and it does. When at idle I get 14 volts though coming from the alternator. I also installed a push button switch to save the wear and tear on the old ignition switch. Cool upgrade, impressed the wife! I still don't trust the car at this point!

When I first had the problem, first thing I did was charge the battery, did not start. Me thinks the ground strap was the solution? Dave

Your charging system should be putting out 13.5 volts or more. I believe you have an internal voltage regulator in the alternator so now would be a good time to have the whole thing checked out.

I did clean the ground strap to chassis for the trans, but believe the trans section of the strap is inaccessible? remember this is a 930 with 915 4spd tranny.
I will jack the car again this evening to confirm this and re check voltages however, even with 12.2 volts the car was starting fine - this non start issue is very hard to replicate.

I am tempted to take the car to the P Shop and have them check the alternator as I am running out of spare time as work will soon be all consuming!

Thanks
Ben

Just fired her up again from cold with battery fully charged to 13volts.

Alternator charged to 13.8v at idle.
It let her run up to temps 80c still charging to 13.5v

Stopped and restarted engine, volts now dropped to 12.8v and falling!
Turned headlights on and volts drop to 12.5v
Stopped and started whilst warm sevreral times and volts stay at around 12.4-5v

Is there anywhere else I could test the alternator or the charging route to confirm alternator is bad?

I have dissmantled my fan to access the alternator on my Carrera, but with the intercooler and all, I may be tempted to take to the 'French wrench' to sort out now we know the route of the problem.

thanks
Ben

I am having the exact same problem and it's really starting to piss me off. I'm going to pull all the fuses and clean all the connectors in the fuse block, checking each wire along the way. I've done everything else already....

Funny you should mention that as I replaced every bullet fuse and cleaned the connections yesterday!
I even changed some of the fuses back to their original lower fuse rating as listed on the cover - I will monitor these fuses as they may have been raised for a reason.
I do not like fuses being over rated as they are designed to blow at a certain amperage for a reason!

I am also still working my way around the chassis to try and clean all of the ground attachments where possible.
regards Ben

Not sure on your setup, but the 'hidden' nut for the tranny ground strap is accessible. I used a 13mm deep socket on a small drive ratchet, barely reached it, but got it.

Thanks will attempt the ground strap - to tranny, tomorrow as ran out of time tonight.
Thanks for the info
Ben

Maybe I missed something but why don't you take the alternator to a shop and have it tested. It could be as simple as poor brushes or a failing regulator. Either could react to temperature.....

On another note - 12.5V is plenty to turn over and start the engine unless you have losses somewhere else from the battery to the starter. You should measure the voltage right at the starter motor while cranking. Then measure it at the battery. If there is more than 0.5V difference you need to check for a poor GND or loose cable at the starter or battery.

Cheers,
Ingo

Thanks Ingo for the reply, the cleaning of the ground strap was to rule out any other weaknesses in the electrical system as this electric system has been 'fiddle with' (poss aftermarket alarm, etc)

I have only just noticed the voltage drop and so wanted to know if there was any other diagnostics I could run before taking to a P shop as I have already spent $$$$$$ in diagnostics which were wrong at shops.
Pelican Parts saved my bacon with my 1st Porsche some 10 years ago (86ragtop)

The car IS restarting with 12.5-12.2v but the fact is the volts are continuing to drop.
It seems the alternator continues to charge 'when warm' IF the motor has not been restarted. If I stop and restart the engine, the alternator does not charge (according to volts tested at battery)

Once the engine dies there is not enough juice in the battery to restart/throw the solenoid

I am also not ruling out that there are/have been other gremlins in the system - like a weak ignition switch (now replaced) or dodgey extra (aftermarket) relay before one of the red fuel relays.
I may even be looking at refurbing the new (refurbed) starter motor - to rule that out of the equation

This is why I need to make the whole electrical system strong to rule out other contributing factors

---- getting there!:rolleyes:

It sounds like your alternator is only charging when cold, so I would suspect the slip ring bushes which are an easy fix either yourself or an auto electrician. Next would be the regulator having some wierd heat related fault.

Thanks for the input from NZ
- just about to employ a NZ chef this afternoon!
- I may take the car to the shop next as running out of spare time!
- Wish I had discovered this months back as I could have probably attempted it myself!
cheers
Ben