Electrical problem?

[MikeP]

The engine is running great! On to the next project! Lets see what you guys make of this one.
Starting with a fully-charged battery the engine starts in just 3 or 4 seconds of cranking. I'll run the engine for 10 minutes in the garage, shut it down, and the battery is too dead to start again. I barely turns over. I tried another battery. Same process same results. Tried grounding the battery strait to the block. Same thing. Now heres where it gets tricky. With the headlights on, when i hit the starter....The lights don't dim. They are as bright as they are with a full battery. Shouldn't they go out or dim completely????
I am close to replacing the positive starter wire. What do you guys think?
Its embarresing to be pushing the car down the street and trying to jump in and pop the clutch.
Thanks in advance,
I can't wait to see what you guys make of this one.
Mike

[pjv911]

Check for a hot connection on battery and starter after the problem happens and to try to crank it. Bad connections make heat because of to much resistance. Did you ever notice that a cheap set of jumper cables will get hot after use.

[adot]

Hey Mike

I dont think its the battery. Lights are still bright after 10 minutes of running.If you were draining the battery, the lights would not come on. What happens if you try starting the car hours later ?
Im betting the car starts. Im with pjv911, check for bad connections. It might be the starter. I had a bad rebuilt one. About once every two weeks, the car would not start. Hot or cold.
Yes, its embarrassing to be pushing the car down the street and trying to jump in and pop the clutch. I lived with this problem for about a year before replacing the new rebuilt starter with one from ebay.

Be very careful under the car and working on connections at the starter. DISCONNECT THE BATTERY !!!! When I replaced the starter , I connected all the wires to the new starter before bolting it in to make sure it worked( bought from ebay). Connected the disconnect battery, turned the key and the starter spun up. Bolted the starter up, reconnecting the last starter wire, remembered I forgot to disconnect the battery. Nothing happen, but it could of very easily. Still sends chills down my back thinking about that day under the car.

GoodLuck

Brett

[Efrain68912]

My experience with non-charging charging systems is that the lights will stay reasonably bright even with a dead battery.

Check the ground strap, check and clean the ground at the battery. You would be surprised at how many problems these two things cause.

Look into buying a starter relay. Made a big difference in my car.

Efrain
68 912 Coupe

[MikeP]

I've heard guys say the relay is the best way to go. What did you use? I've hear the ford relay is the simplest.

[MikeP]

Efrain,
What do you mean about a non-charging system? That is an alternator there is it not? Mine puts out .34 volts at idle, this is charging the battery isn't it? Or does it only supply enough for the car?
mike

[C. Clark]

Mike,
What was up with your engine? several post ago I remember the engine was making a whining noise and before that you thought you had a bearing problem. I wouldn't turn over... clutch or something caused the problems.
Just curious, I never heard the diffinitive reason for the problems.
Chas

[Efrain68912]

Mike-

The non-charging system is the system that Porsche graciously included on my 912. It flares up occasionally - like when I'm in the drive through at In-n-Out at 10:30 p.m. and the stereo turns off... or when I'm on a date and a turn of a key causes the solenoid to pop but no engine kickover (damn lucky I parked downhill, just popped it into gear)...

Seriously though, .34 volts sounds really low to me.

Efrain
68 912 Coupe

[wastintime]

What do you mean when you say "puts out .34 volts at idle?" Voltage isn't really an indication of whether or not your system is charging. Unless you check the battery and notice the battery is varying in its voltage output. Volts are just the amount of energy per mole of electrons. Amperage is what you should be looking at to tell if it's charging or not. Depending on the diameter of the generator it should put out different amounts, but I think both are over 30amps @ x RPMs.
Here is a stupid question, but it happened to me once, is the battery in backwards? It sounds like your battery is discharging at some point and you need to find where that is.

Andrew

[Green 912]

You have given 2 good clues that in some ways contradict each other. In one way you have described the classic hot start problem but in another you have described a charging problem. My bet from what you describe is a possible charging problem based on the installation of the second battery, successful restart and the reading of .34 volts (if correct) on the running system.

If it won’t crank, check the battery voltage both with just the lights on and when attempting to crank the motor with the lights on. If same when cranking as not, suspect the starter connections and leads, if it drops considerably when you attempt to crank, recharge or replace the battery, start the car and test the charging voltage with the car running. It should be about 14.5 at 3000RPM or so. If you are starting out with a charged battery, leave the volt meter on the battery and see if the voltage is (1) not going up to 14.5V with the car running at more than idle and (2) dropping continuously as the car is running. Both would indicate a problem in the charging system. If you have nether symptom then move on the hot start testing. If you have charging problems then it will require more testing on your part in order to give direction on where to look.

If the car will not crank when hot regardless of battery charge, start with all the connections from the battery to the starter and all on the starter as well (ground strap too) clean and tighten as you go. If you still have the problem with hot cranking then check the starter and its bendix.

Not on the top of the list but another thing to check is the ignition switch. I have seen Ig. switches get hot and fail as they get old and on a 912 it will be old. If you have the problem, just reach under and see if it is hot and if so push on the back and wiggle it some and see if it will work. The backing plate on the Ig. switch has a bundle of connections on it and it can loosen and make intermittent and weak connections.

Amp output from the generator will vary widely depending on the load placed against it but the voltage will vary little. In order to charge a 12-volt battery you must overcome the batteries internal resistance. To do so in an automotive battery you need to put more than 13.4 Volts against it in order to induce current flow into the battery. A generator that is responding to the regulator correctly and capable of charging the battery will produce greater than 13.5 Volts and normally 14.5 Volts regardless of load.

Don’t start replacing things without knowing what is wrong first. That is the best way to introduce a second problem, and having 2 related problems will make each very hard to find.



Kurt

[MikeP]

Thanks for all the input guys, looks like i have a few things to check on tomorrow.

C Clark, this thing has been one problem after another. Since i bought this car unoperable and have never owner or worked on a porchse, I have had no base line to compare to. A tight spot when turning the engine over by hand was my first delima. Pulling the engine out (again) I pulled her apart down to the case (again), couldn't find anything wrong. Put when i put her back together the tight spot was gone. I believe it was the clutch dragging. When I first pulled it out and cranked it over i noticed the clutch fork pulsating in and out. Neverless the problem is gone. Next the high pitch noise. I just went away one day! Very bizar! Could never determine where it was coming from. And it would go away when accelerating with or without a load. Very odd. Next the Carbs have been the focus of most my time. I've rebuilt them and have them synched, but still missfires at high throttle. Could be timing...its just hard to work on it when i can only get one start out of her between charges. The Starting problem has always existed, i'm just getting to it now. I've bought a brand new battery and new cable and am going to try to see if it makes a difference.

Kurt and Andrew, Thanks for the electronic suggestions. No My battery isn't in backwards. Nothing would work then. I need to pull out that old principles of electricity book from college. I'll do a few more tests and let you guys know what i come up with. I agree, that the battery is discharging somehow. Possibly a short somewhere?

Excuse all the gspelling error i hope you get the point I'm not going to double check...I'm to excited to get out to the garage!!
thanks again mike

[C. Clark]

Mike,
Thanks for the update, I as you, am learning as I go. I've worked on many cars but never a Porsche, the learning curve has been interesting and to say the least. Thank goodness for this site, it's has made fixing many things much easier do to the extreme level of experience available here.
I would bet the problems you are having is connection related. My car was stored for 5 years when I a aquired it. The electrical stuff was wierd, most problems were cured by cleaning connectors and the fuses and contact points throughly. Older Porsches remind me a little of old Jags, and their electrial is infamous.
Good luck with the car,
Chas

[wastintime]

Mike,
I hope the new battery works for you, if not it's at least a good way to test something. Check the voltage of the battery once you install it, and if it won't start again and you think the battery is dead then check again. A healthy fully charged battery should put out 12.6-13 volts and should be considered discharged around 12.39(70% charged) volts. If it falls below 12v then it's less than 25% charged. If it isn't charged, then you can check the charging system, and then look for a discharge.
I actually wouldn't dismiss the battery position. Just becuase I had someone install a battery in my car once and it started doing the exact same thing you're describing. It took about fiftteen minutes for the battery to drain completely. As it turned out the problem was that the battery was in backwards. Since it's a negative ground system the battery will work if it's in backwards, and shouldn't be able to harm the regulator, but will discharge constantly.
Good Luck

Andrew

[MikeP]

Chas,
Yes this Site is great! Its helped a bunch. But listen to this bit of luck. I'm on a test drive. I stall it at a stop sign two blocks from home. Battery wont start it so here i am pushing the thing down the street and a guy yells from his window "Hold on, I'll give you a hand" He comes out and tells me he builds these things for a living(refering to the porsche). He owns a custom porsche shop and has a race team...what luck! AND he volunteered his time to help me out tuning her up...Boy am I lucky or what? What are the chances?
mike

[MikeP]

Andrew, wouldn't the starter turn in the oposite direction if the battery was in backwards? I'm pretty sure i have it in right. The negative is grounded strait to the body...right? and the positive runs down strait to the starter...right?

[wastintime]

Mike,
The direction of the battery just governs the flow of electricity into and out of the battery (sort of, and basically)... electricity is always trying to flow out of the anode and towards the cathode and so reversing the battery is obviously going to affect how it flows. It's a bit more complicated in positive grounded cars like jags because you can end up destroying your electrical system with it in backwards. You probably do have it in correctly, I was just making the suggestion hoping you'd luck out and that was all that was wrong. Yes, the negative terminal grounds directly to the front body of the car. And the positive wires run back to the starter.

Andrew

[jac912]

Just a tip to add to the above ....with engine running you should be able to disconnect the battery as the generator supplies the coil.
If the engine cuts out it was running off the battery only. Cause could be gen. polarity, regulator, or connection from regulator to starter which returns charge to battery. Generator light could be a seperate issue. Good luck!

[MikeP]

Today i tried a little more trouble shooting. Heres what i did:

Took the following readings:

New battery full charge disconnected 12.90 vdc
connected ignition off 12.78
connected ignition on 12.47
Egine running at idle 12.26
Generator at idle measured across D+/D- 12.60
Engine off after 5 min run, at battery 13.10
At the starter durring starting 11.10

This seems right on to me, everything is close to where it should be(i think).

Where does the DF come into play? There is .39 vdc from it to ground at idle and increases with rpms.

12 vdc across DF/D+ at an idle but as the rpm increases the voltage decreases. WHY?

The next test i started and ran for 5 minutes. Shutdown. Was unable to start again. Tried installing fresh battery, with same result. No start.

All the connections are good and clean. To try and eliminate possibility of high resistance in ground or hot lead, I used one battery for ignition power and one for starting, wired directly to the starter, with a new clean cable.

It seems like she just won't start when warm. The starter is new, but possibly lacking power somehow. I have a big bore kit, does the higher compression require a bigger starter? Or do i have this hot starting problem you guys talk about?? The engine is hardly hot though, after five minutes how hot can it get??

So what do you guys make of this?

[adot]

MikeP

Try touching a new wire to the starter solenoid control terminal from the new battery( yellow wire on solenoid, i think). Please be careful doing this, if the cars in gear, starter starts, it might kill you.

Maybe a bad new starter ( rebuilt ?)

GoodLuck

Brett

[pjv911]

I am 95% sure that a 911 starter from 74? and up is a direct bolt in and has 50% more cranking torque. I bolted a 77` 911 2.7 starter directely to my car. The starter is also a little heavier.
Thats just a suggestion if you change it again as I am not suggesting that the starter is the problem although maybe it is.

Also Did you feel the pos- neg wires for excessive heat ?