997 slow engine cranking - Page 2 - 911/Carrera GT - PistonHeads UK

My 07 997 2S cranks over really slowly and almost fails to start but always does. I've fitted a new Bosch 80amp battery but no better. It sits on a battery trickle charger which when started after a few days it cranks over at normal speed. Go for a run and then try to start and it's really slow again. No warning lights on at all and runs perfectly. Anyone any ideas on where to start looking? Could it be a faulty alternator or is there a common reason for this?

Earth strap gets mentioned a lot, worth checking this?

I'd have fitted a bigger battery. The 100 amp/hour S5 Bosch is better.

Cranking at normal speed after charging but more slowly after running would suggest a charging issue. Have you measured the battery voltage before and after?

The +ve lead from the battery to the starter/alternator can develop in line resistance as corrosion gets into the terminals. With a voltmeter take a measurement across the battery - engine running you should see 13.5 -14.5 volts on a good system. Load the electrics - switch on interior fan, lights, heated rear window, heated seats and measure again once the engine is warm - again running you should see at least 13 volts (bring the revs up and monitor the voltage - should regulate at around 14 volts at 2500 rpm) Note the results Open the rear lid and locate the alternator (LHS of engine bay in front of the airbox as you look in) you will see a thick black cable coming out of the back of the alternator - take a voltmeter measurement from here to the lid lock (a good earth point); if the cables are bad your figures will be much higher at the alternator (the voltage drop along each of the cables should be <0.3 volt - there are three; battery to power distributor / power distributor to transmission connector / transmission connector to alternator *) Eg: Engine running, voltage at battery 13.8v Loaded, running (2500rpm) voltage at battery 13.8v Running, voltage at alternator 14.0v Happy days If you have: 12.5v 12.6v 14.5v Chances are one (or all) of the +ve cables are on their way out. You could just measure between the alternator lead and the battery +ve terminal (if you have long multimeter leads but most people don't); this will instantly tell you the volt drop (potential difference) of the cable 14v at one end and 12.5v at the other will give you a pd of 1.5v = faulty To check each section of cable, measure from one end to the other (multimeter red (+ve) connection at one end, black (-ve) at the other) the displayed voltage is the pd - you are looking for at the most 0.3v

Pope said: The +ve lead from the battery to the starter/alternator can develop in line resistance as corrosion gets into the terminals. With a voltmeter take a measurement across the battery - engine running you should see 13.5 -14.5 volts on a good system. Load the electrics - switch on interior fan, lights, heated rear window, heated seats and measure again once the engine is warm - again running you should see at least 13 volts (bring the revs up and monitor the voltage - should regulate at around 14 volts at 2500 rpm) Note the results Open the rear lid and locate the alternator (LHS of engine bay in front of the airbox as you look in) you will see a thick black cable coming out of the back of the alternator - take a voltmeter measurement from here to the lid lock (a good earth point); if the cables are bad your figures will be much higher at the alternator (the voltage drop along each of the cables should be <0.3 volt - there are three; battery to power distributor / power distributor to transmission connector / transmission connector to alternator *) Eg: Engine running, voltage at battery 13.8v Loaded, running (2500rpm) voltage at battery 13.8v Running, voltage at alternator 14.0v Happy days If you have: 12.5v 12.6v 14.5v Chances are one (or all) of the +ve cables are on their way out. You could just measure between the alternator lead and the battery +ve terminal (if you have long multimeter leads but most people don't); this will instantly tell you the volt drop (potential difference) of the cable 14v at one end and 12.5v at the other will give you a pd of 1.5v = faulty To check each section of cable, measure from one end to the other (multimeter red (+ve) connection at one end, black (-ve) at the other) the displayed voltage is the pd - you are looking for at the most 0.3v Thanks for this, very helpful reply. I'll check this as you suggest tomorrow and let you know the results.

The problem you describe is more than likely down to the poor main battery cable from alternator to starter motor then to junction box on side of gearbox... there is a fault with the crimped connection..! the cable is around £66 and fitting is roughly 4 hours. Fixed a few that did this. ok when cold and as it heats up the joint must create high resistance and can not carry the current needed to crank engine. Lifted the above from a thread, on 911uk, as I had the same problem last week, on my 997.1 turbo. Although, now I've been told, that the above applies more to the 997, but not the turbo, plus the above is an engine out job. Mine turned out to be a corroded lead and starter.

If the voltage regulator on the alternator is failing, that can cause the alternator output to drop after 10-15 mins running as it gets warm. What does the voltmeter in the car read?

There isn't one.

I have 12.7v at battery with engine off, 14.9v idling with no load and 14.6v with both heated seats and all lights on. To me that shows the alternator is working correctly but I know nothing about electrics so over to you guys (and girls).

But what happens to the voltage when the cables and alternator have absorbed heat from the engine? This was when the alternator output on my 996 dropped as low as 10.5v.

I've been for a long'ish run to warm up engine fully. On return it reads 13.2v engine off. 14.6v engine on no load 14.3 engine on full load (lights/seats) Left for 10 mins readings are almost identical.

It's the wiring loom as mentioned by ralleman above. Porsche supply a heavy duty replacement to solve this common problem. A local independent near me has replaced quite a few of these on early 997's and it always cures the slow cranking issue.

I have noticed the same issue however I am starting to wonder if it's just a tight engine, I also find if I don't start the car for 2-3 weeks the cranking is very slow almost to the point of where I think the battery is flat. If however I crank it for 2/3 seconds and then wait for 20/30 seconds and try again it cranks a full speed. guess it could be a cable issue between the starter and main terminal but to me it feels like the engine is really tight as the lights flicker etc on the first initial crank and I know the battery is fully charged and new from the trickle charger.

Crazy4557 said: I've been for a long'ish run to warm up engine fully. On return it reads 13.2v engine off. 14.6v engine on no load 14.3 engine on full load (lights/seats) Left for 10 mins readings are almost identical. Well, for me your charging system and leads sound about right and you have either a dying starter or an earth issue. The rear lead test is the one that will ultimately give you the +ve lead diagnosis - the alternator output and its difference from the battery figure but 14.3 loaded, warm for me is a test pass. Measure the pd from the engine to earth during cranking (the higher the voltage the worse the earth condition - usually highlighted during high load conditions like pulling serious amps when turning a starter); ideally less than 0.5-0.6v; any more and your earth leads or connections are suspect. If the earth is OK you are probably looking at a starter that is beginning to lose efficiency - more heat and noise than spinning nicely.

http://www.911uk.com/viewtopic.php?t=107528

I had exactly the same issue. Slow cranking when the engine was hot. It was the Earth lead.

I had same symptoms on a Mezger turbo 997, it was the starter motor.

As it's under warranty the dealer's taking it back and assures me the starter motor's to blame and will be changing that. A few people have mentioned this as a potential culprit so I'm happy to see what the result is. When it returns I'll let you know how I get on.

So... What happened? Assuming it was the starter motor as you didn't have time to post since the fix worked - hopefully too busy enjoying the car ;-) I have the same issue with my Mezgar 997tt. From reading these threads, it is either the starter motor or the earth cable. However, it does seem to be very prone to dropping charge. I have no bought a trickle charger but surely I should not be faced with a flat battery after a few weeks standing? Anyone know how many volts the starter motor uses to start the engine in say four cranks?

The same diagnosis applies; if the voltages are correct at the battery when the system is 'hot' then the +ve cables are generally okay. The -ve cable can be tested - but rarely fails. 997 turbo/GT cars have a different cable arrangement over the NA cars and seem less susceptible to the cable issues from experience. Get the battery tested - if that passes fine then the starter motor is likely the culprit - do you also get the occasional 'click' instead of cranking as expected??

Hello everyone, I just bought my first 911 997. The car seems to have a slow start vs. other 997s that I have tested. I did a very short video to demonstrate exactly how much time does it take between it starts cranking and the engine going back to live (which is I think 2 seconds, 2-3 cranks...?). Here is the vid: https://youtu.be/xcGyZve3Iws Based on the above comments and other posts that I have seen on the topic, I cannot figure out whether its a matter of "they all do that" of if there is something that needs to be fixed. Would appreciate any support! Thanks in advance. Nuno

Sounds totally normal; if anything reasonably quick cranking for a 997.

Thanks for the feedback Will!

Willwors said: Sounds totally normal; if anything reasonably quick cranking for a 997. Agreed, mine was much slower until I had the starter motor changed. Sounds just like yours, maybe slightly slower (new battery + starter motor)

Thanks LPAK. Mine does have a brand new battery with higher than standard capacity so this may help. I guess I am too used to "normal" modern cars that you just press the button and they fire up. Best Nuno