Philster

If cold cranks are consistently much stronger than hot cranks, it is a cable issue.

That's it. Anyone being presented with this problem --- Indy, dealer, Joe Shmo -- needs that driven into their head.

Example: Cold crank and it's fine.... run for 45 minutes til real hot, and it barely cranks (say, when you get home just before parking it for the night, shut it off, then attempt to restart and it is weak), then you come out the next morning to a strong cranking engine... that is the cable.

The alternator issue and a weakened battery would not result in this outcome again and again.

A cable that won't let full juice flow to the starter because the cable is hot is in need of an upgraded cable.

If you had just ONE example, where one crank was strong and the next was weak... and you looked at the problem in just that narrow bubble, the conclusion is usually a battery going south. However, a consistently strong/strongish crank on cold startups and consistent weak cranks on hot startups calls out the cable as the issue.

EDIT: I just had a thread on this. I tightened things as per the bulletin and the problem is mitigated. My hot starts are slightly weaker than cold starts. I'm losing something to the heat/cable, but not enough to go bonkers just yet.

motopix

Cable, starter or crank/flywheel position sensor are your three choices. Make sure whomever tests it, does so when the car is hot. If mine cools down for 20 minutes, it's starts a tiny bit slowly but nothing like the slow, stuttering start after a 5 minute heat soak while filling up for gas.

CP911

Thanks guys. I'm going to take it for a spin now that it has been sitting overnight and will observe cranking behavior again. Already have an appointment with the local indy shop for this Friday morning to have it diagnosed professionally. Let's hope I can get the issue resolved sooner or later. Not having confidence that my new car will even start is a really sucky way to enter Porsche ownership.

motopix

I know it sucks but at least take heart in that no matter how much mine has slowly ground to a start, it's always started.

But already putting money into a new toy is never fun - unless it's for shiney go-fast parts.

DC911S

Got that right, as I've put off having my high flow cats put on to get that damn starter cable fixed. I've ignored it too long. Time to get'er done. I hoping to get Porsche of Tyson's to see if Porsche NA will give me some break on this repair, since its a known problem. One a side note, I found a thread on another forum where the guy took off the airbox, plenum, and TB...then unbolted the wire from the starter....then used a big crimper to ...well crimp it down much tighter....and it solved his problem. I'm wondering of trying that but using a torch and good solder with resin flux would fix it. The problem seems to be the crimp that holds the wire to the connector jiggy that then bolts to the starter...is not tight enough and gets corroded. That of course makes more resistance....which all EE's know then draws more current....and heat makes it worse....more resistance, more heat,...

Ericson38

EE here-


Lets say a new battery pulls down nominally to 10.5 volts while cranking the starter, which is pulling 250 amps turning the flywheel.

That initial 2 volt drop (from 12.5v) is due to the internal resistance of the battery itself. Vdrop = I x R, so battery internal resistance is around 0.008 ohms (8 milliohms). The lower the better. Batteries warm up under heavy discharge.

So the starter internal resistance (including that from back EMF of the rotating motor) ideally is E/I or 10.5 v / 250 a = 0.042 ohms (42 milliohms), assuming the cable has 0 ohms loss, for a moment.

If the high resistance lug connection on the cable is even 0.042 ohm (the same as the starter equivalent DC resistance when at cranking speed), that will drop the current flow through starter armature to half what it was, ideally, disregarding any other lump serial resistor elements.

Of the 11.75 volts that would have been available at the starter solenoid (0.008 ohms x 125 amps), now only 5.87 volts will be available there, and the other 5.87 volts will be dropped (could be measured with a meter) across the high resistance defective lug. The heat at the lug (5.87 v at 125 amps) is significant (733 watts), and will in time melt the insulation around that end of the cable.

Plus, hot wire resistance is higher than cold wire resistance (temp coef is positive), so it is a self feeding problem, the longer the engine is cranked in this condition.

Same problem occurs on the Westy Camper, so I just bought another (AutoZone) red battery connector lead (lugs on both ends), and run it in parallel to the stock one. Probably can't run a lead parallel to the existing one in the 911 easily, but haven't looked at it either.

DC911S

EE here too, so very good summary. Yes, I have no ides if the crimped connector on the starter can even come off the cable and there is no room to add a second one. IF it comes off, I would clean the whole thing with a dremel wire tool and use good solder with god flux to solder it in. I HATE crimp connections even more that those ****ty snap-lock wire spiltter connectors too. It a cheap way to do things.

Devil Boy

I replaced my cable and it did not improve my slow cranking. I already had the new and improved cable too. Replaced the starter and it fixed the problem. Just something to consider.

https://rennlist.com/forums/997-foru...l#post11346593

DC911S

Yes, I may have them do the starter and cable. All at once.

CP911

Excellent. Thank you! What year is your 997 though? I noticed you already had the new style cable, so hoping my 2007 will have it too.

Is it possible that it's not the starter or cable, but simply a bad connection at the contact/lead? Just thinking it might have been you brushing the leads and reconnecting them properly for better electrical conductivity that really did the trick...

DC911S

It's not the cable per sa, it's the crimped connector on the cable that bolts to the starter. It's not properly crimped on. One guy re crimped it and that seemed to fix it. I'll find the thread on another site.

Devil Boy

2006. Previous owner had the new cable installed under warranty for slow cranking years ago. I also replaced the cable because the general consensus on the forum was that the cable is always the culprit. I can confirm 100% that the leads were clean and tight when I installed the new cable and it did not improve the slow crank when the engine was hot. Replacing the starter fixed the problem.

Hot rod guys with small block chevys and headers that are closely spaced to their starters have the same issues with heat soaking and slow cranking. Our starters sit there cooking on top of the engine for the past 8+ years, after a while they go bad. It's gonna happen.

CP911

Well, you've inspired me to swap out my own starter and cable. This morning I took it to the local indy shop (European Performance in Raleigh) who specializes in Porsche and BMW and I was not feeling like they were being straightforward enough with me. I explained what the issue likely was and all they could tell me is they charge an hourly rate of $99 to diagnose. They said, "Sometimes it takes an hour or two, sometimes three or four." Wasn't having any of that. In my opinion, they should have some clear idea of how long it would take to measure a few voltages with a DMM near the starter, but what do I know?

I can get a new OEM starter for $250 or I can get a remanufactured one from O'Reilly's for less than $150. New cable is $100. So $250-$350 max for the parts I need. Definitely seems like the way to go!

Thanks again for the DIY tutorial and for taking the time to comment. I'm still relatively new to the forum, but liking this place more and more each day.

DC911S

Getting a new cable installed at Porsche of Tysons...for about 1200 or so. I asked them to contact Porsche of NA to see if they will help pay for it. Never hurts to ask......

CP911

$1200? Good Lord. Hey, if you have the money to live around Tysons Corner! (Assuming you are talking about VA...)