dan_189

Hey all,

Drove for about an hour over the weekend, parked at my destination and was on a hill, I got slightly distracted and stalled - ha! fool.
Upon re-start I had quite a severe voltage drop but it did start. About an hour later though it fired up with no problem? Could this be a problem because of the stall or something more sinister?

Things of note:

- Car is 2004 C2 RoW manual with ~87,000kms (~54,000 miles)
- Starter to alternator cable has already been changed just over a year ago - this was a major issue awhile back solved with a new cable
- Battery was fully charged last weekend with my c-tek - but is definitely not new
- The ground straps I don't think are an issue as we generally don't see too many corrosion issues here in Australia.

Am I right in thinking because of the voltage drop the starter might be the culprit if the cable has already been replaced?

Thanks!

Porschetech3

First, before trying to diagnose a starter or starting circuit, test the battery using a capacitance/conductance tester (not a load tester). A capacitance/conductance tester is more accurate than a load tester. It should read at least 80% of the rated CCA.ie a 1000cca rated battery will read over 1000cca new and when below 800cca are considered needing replaced. Porsche H7's nominally are about 750cca so anything below 600cca would be considered faulty.I don't know if you have an Auto Zone over in Aussi, but here we have them and they do free battery testing using a capacity/conductance tester.(but I have my own Midtronics MC-340 tester)

After verifying/replacing battery for available power then do voltage drop testing (you probably have done this when diagnosing your cable).If voltage drop testes passes then do starter amperage draw test.

Mike Murphy

dan_189

Thanks Porschetech3 and murphyslaw1978, I did do a voltage drop test when I diagnosed the cable (because the dealership I went to diagnosed the starter) and I didn't trust them as they diagnosed a broken clutch assistance spring (heavy pedal) as a worn clutch.

However post replacing the cable over a year ago until saturday its been starting perfectly. So ill move onto testing the battery - we have a few auto places we have "autobarn" and "supercheap auto" FWIW!

How can I do a starter amperage draw test?

Interestingly I was talking to another 996 owner who has experienced something similar - difficult start post a stall when hot although I wasn't sure if it was struggling to fire or if the voltage dropped like in my case.

When I got home from the destination (same distance, very similar temp) my car sat for about 20 mins and then fired up perfectly, although maybe that was enough time to dissipate heat from what ever would have caused the voltage drop?

Only more testing will tell damn intermittent issues!

5CHN3LL

More than a few of us have had issues with heat soak and starters. In my case, replacing the starter eliminated the hot start issue.

What are the specifics of the observed severe voltage drop?

dan_189

I had the issue awhile back and the cable fixed it up until now, hopefully it doesn't persist but usually these things don't go away without some sort of intervention.

As for the noted drop there was a dive from the volt gauge further than usual on startup (one of the times its been useful) coupled by the gauge cluster illumination dimming and also the noise of the engine turning slower than usual.

All pointed to something electrical.
​​​​​I actually gave it a bit of gas (whether that does anything im not sure) but it came back to life but only just. Sounded like if it didn't kick over the first time I tried it would have just given me the ticking noise like when the battery is dead.
​​​​​​
​​​​I have a feeling it's the starter, I hope to wrong though...

Porschetech3

To measure the starter current draw you will need a meter with an inductive amp-clamp. Most standard DVOM's do not have this. You need one with a range of at least DC 300 amps. The amp-clamp clamps around the pos or neg cables and measures the current flowing through, Should be around 150 ampDC with good speed.

dan_189

Thanks for the info Porschetech3! Am I measuring the voltage the starter is pulling from the battery, so the unit gets connected to the battery positive or negative? Then taking the reading while the car is getting started?

JohnCA58

While measuring the starter draw, you will want to disable the engine so it won't start while measuring draw. such as fuel pump relay.

Porschetech3

During the starter current draw test you will not be measuring voltage, you will be measuring amperage, using Ohm's Law I=V/R..Where I= amperage, V=voltage, R=resistance...996 starter power is 1.7KW @ .082 resistance. ..12v/.082R=146amp

The current/amperage will be the same on pos and neg cables when engine is spinning (disable fuel pump so engine does not start as John suggested) IF amperage is too high (ie 200 amps) it indicates starter resistance too low OR engine is resisting turning due to mechanical resistance.

IF current/amperage is too low (ie 100amps) and starter is spinning slow it indicates starter OR cables have high resistance (voltage drop test would indicate cable resistance beforehand)

IF current/amperage is too low (ie 100 amps) and starter is spinning very fast it indicates low mechanical resistance ( low compression).

fpb111

dan_189

Thanks all, I'll let you know how I go going to start with the battery test then move onto testing the starter.

Hopefully it was just a one off but see how we go!

Porschetech3

That particular one doesn't show DC amps, but this one does.https://www.zoro.com/fluke-digital-c...25/i/G4573816/

Mike Murphy

dan_189

I had also initially thought alternator because the drive distance/time was decent and all highway and this the battery so be maintained.

Then when it started when it cooled I starting thinking maybe not but I will definitely check the voltage it's producing. I could see from the gauge it was decent when running and all auxiliaries off I do see it close if not over 14v.
​​​​​​