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OK, 2005 cayenne turbo. intermittent problem with starting. had independent Porsche mechanic replace the battery, alternator, starter and starter relay about 9 months ago. very intermittent problem which happens about once every 3-4 months. seems to be more pronounced in very hot weather (90-100 plus degrees Fahrenheit).

 

when it happens the engine simply will not crank at all. in spite of that I will still have radio, horn, power windows, AC, etc, full electric.

 

in the past I have simply used a Rockford battery jump starter (given to me by the mechanic) and this starts it right up. today, I parked in a multilevel  parking structure at a mall and the outside ambient temp was over 100 degrees. I parked with another vehicle in front of me, as well as 1 vehicle to each side. not much air circulation. temp inside the parking structure exceeded that of outside I am sure. the Rockford, unlike past times, would not immediately start the engine. I almost called AAA roadside assitance.  fortunately, after about 6 tries with the Rockford, I was able to start the car.

 

drove the car from that 100 degree climate for about an hour to an 80 degree climate. parked it outside. turned it off. wanted to test starting it; she started right up without hesitation. repeated this several times with no issues.

 

anybody have any ideas about this intermittent ghost in my machine? I really love this vehicle and I'm willing to consider replacing additional parts if necessary (ignition assembly, etc).

 

other than this intermittent problem, this car with 175K miles runs fantastic.

 

any and all thoughts are appreciated. thank you.

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Just a hint because happens with me in a similar way.  Extreme temperatures making the wires in the car very soft and after almost 12 years some look very briggle like in my car. I would recommend to check the wire system inside the fuse box in engine compartment and everything inside the engine bay. 

Briggle wiring and very hot temps: the wiring which is maybe without proper isolation is getting very very soft and touching any ground or something else. 

Just an idea.

 

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I appreciate your advice and will act upon it to have my mechanic check the wiring. it does make sense that extreme heat could cause a brittle or partially non-insulated wire to ground out against another wire or metal part. the car is a 2005 so 12 years old. 

 

however, why is the Rockford portable battery starter able to jump start the car when the car will not crank on its own when the ignition key is turned? I guess it could be a wire from the starter relay to the battery such that when the key is turned the relay "sees" no battery, and when the Rockford is put in place now there is a battery?

 

does anyone know the electrical path as relates to starting the cayenne? I sure don't.

 

is it that electricity flows from the ignition key to the battery to the starter relay to the starter?

 

I do believe that ekstroemtj may have the right idea about this problem being faulty wiring inasmuch as the major components (starter, battery, starter relay and alternator) have all been replaced. the wiring has not been replaced.

 

thanks for your feedback ekstroemtj. once again, I welcome and appreciate any and all comments/ideas from others as well.

 

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2 hours ago, mrzeus2012 said:

I appreciate your advice and will act upon it to have my mechanic check the wiring. it does make sense that extreme heat could cause a brittle or partially non-insulated wire to ground out against another wire or metal part. the car is a 2005 so 12 years old. 

 

however, why is the Rockford portable battery starter able to jump start the car when the car will not crank on its own when the ignition key is turned? I guess it could be a wire from the starter relay to the battery such that when the key is turned the relay "sees" no battery, and when the Rockford is put in place now there is a battery?

 

does anyone know the electrical path as relates to starting the cayenne? I sure don't.

 

is it that electricity flows from the ignition key to the battery to the starter relay to the starter?

 

I do believe that ekstroemtj may have the right idea about this problem being faulty wiring inasmuch as the major components (starter, battery, starter relay and alternator) have all been replaced. the wiring has not been replaced.

 

thanks for your feedback ekstroemtj. once again, I welcome and appreciate any and all comments/ideas from others as well.

 

Check the earth strap from battery to the chassis in front of the drivers seat. High resistance or corrosion causing high resistance in that cable can cause no starts, the cable may feel warm when the car is running also. Check the positive cable as well! 

When you use a spare battery for jumping you by pass that cables high resistance to an extent.

Another possible common issue is temperature sensor or crank shaft position sensor fault(seen a lot on other vw models).

The other alternatives is a long list of wiring and components which could be failing under high heat conditions. Good luck with your search hope you find it. 

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the mechanic had suggested replacing the grounding strap (which is what I believe you are referring to as the earth strap). is this something that is under the carpet just in front of the driver's seat?

 

thanks for your input, much appreciated.

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7 hours ago, mrzeus2012 said:

the mechanic had suggested replacing the grounding strap (which is what I believe you are referring to as the earth strap). is this something that is under the carpet just in front of the driver's seat?

 

thanks for your input, much appreciated.

Yep. 

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getting back to this post as per the suggestions of one on the mechanics that has been working on this vehicle for many months. I am now assured this intermittent starting problem is totally fixed. I did receive an unlimited mileage 2 year warranty on the entire starting system from the owner mechanic when I picked up the car today.

 

2 additional problems were found which has now corrected the intermittent starting problem that I previously experienced.

 

first was a cracked PC board next to the fuse block.

 

the second, perhaps bigger problem was the connector wires located between the 2 firewalls. as I understand it, a bolt had come loose causing the wires to arc. as I understand it, this loose wiring connection resulted in a voltage drop from approximately 12 volts to 3 volts , which is definitely not enough to crank the starter.

 

so, my odyssey as relates to this intermittent starting problem involved the following:

replacing the battery

replacing the starter and starter relay

replacing the alternator

cleaning the battery grounding strap

replacing the PC board at the fuse block

and rewiring or fixing up the wiring located between the engine firewall and cabin firewall

 

perhaps the best thing that happened to finally locate this ghost in the machine was for the car to totally fail without any ability to jump start it. I think this may have provided the mechanics with an opportunity to hone in on the problem and isolate the 2 problems that resulted in this starting problem. of course a lot of expensive process of elimination was incurred along the way with the replacement of some pretty expensive parts which may or may not have been necessary.

 

hope this is helpful should anyone else encounter an intermittent starting problem with their Cayenne.

 

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I had a similar problem many years back with a turbo diesel engine on a different vehicle.   When cold it would always crank, but when hot on occasions it was absolutely dead.  Did all the usual on earth straps, battery and its connections and starter motor.

 

I eventually found the problem.  It was the solenoid spade connector on the starter motor.  When hot the female part of the spade connector was expanding and losing its "clench" on the male spade.  As a result there was insufficient connectivity to energise the solenoid.  The problem was solved by closing the female connector with a pliers.  The problem never re-occurred.

 

Glad you solved your problem, but the source was not dissimilar to mine. 

 

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you solved this problem for a lot less dollars than it cost me. I guess that's the price one pays when one is not mechanically inclined and dependent upon the expertise of mechanics. 

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