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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22735
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a porsche s cayenne 2008 with 4.8 engine The problem

Customer Question

I have a porsche s cayenne 2008 with 4.8 engine
The problem im having now is that it will not start.
What happened before was that the car started having trouble starting from the first time i had to try 4-7 times berofe it would start. Eventually it got worse and my starter motor died.
Bought a new starter and fitted in.
Now it will not start at all. It cranks and wont start.
Got it diagnosed and had camshaft sensor and crankshaft sensor faults. Replaced both of them still not starting and keeps on coming back with the crankshaft and camshaft sensor faults.
Ive checked the spark plugs there are no sparks at all.
I have read everywhere about it and cant find out what is wrong with it. The other problem is that im from UK and i drove with my porsche to ukraine and it broke down in ukraine and now i cannot find a place who would say that they know what is wro g with it and they can fix it they all want to have a look at it but not promising to fix it or at least giving me the max price what could it cost. As these guys are smart as soon as they hear or see its a porsche cayenne the only thing comes to their mind is that we can empty his pockets.
Could you please help me find out what the actual problem is do that i can find a garage that can fix it.
Submitted: 8 months ago.
Category: Car
Expert:  Nicola-mod replied 8 months ago.
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Customer: replied 8 months ago.
Yes i can still wait
Expert:  Nicola-mod replied 8 months ago.
We will continue to look for a Professional to assist you.
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Expert:  Matt replied 8 months ago.


OK as you've already replaced the cam and crank sensors the next thing is to check if the ECU has electrical power with the ignition on

if you use a voltmeter in the engine bay fusebox to check if there's 12V on the ECU fuse

if you have ECU power but still no spark then follow the wiring loom back from the crank sensor and check it for damage and corroded connections between the sensor and the ECU

and if this is OK then the best test is to disconnect the ECU and also measure the continuity between the ECU socket and the sensor connection

if the continuity is there, then we're into a replacement ECU

Customer: replied 8 months ago.
Thanks for coming back
I've got it to the garage they checked the ecu and the wiring for the crankkshaft it is all good
Expert:  Matt replied 8 months ago.



so the ECU has power and the wiring between the ECU and sensor checks out OK?

so if this is true then ideally the next step would be to plug in a scan tool thats capable of monitoring and check to see if the crank speed signal is coming in during cranking

if it is and the ECU still isn't sparking I'd next check to see if the injectors are clicking so checking to see if the ECU is trying to fire that side

if the injectors are not triggering then I'd say either the ECU has a fault or the security system is preventing the start

however if this was the case normally the engine wouldn't crank / turn over either

Expert:  Matt replied 8 months ago.

do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Customer: replied 8 months ago.
My problem still hasn't been solved Matt
Expert:  Matt replied 8 months ago.


have you had a chance to see if a crank signal is making it back to the ECU as I've suggested ?

Customer: replied 8 months ago.
HiYes there is a signal going to and from ecu
Expert:  Matt replied 8 months ago.

Ok so if there's crank speed coming into the ECU

and you can communicate with the ECU to view this then the ECU must also be powering up as well

so the next step is to check if its injecting

if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If you remove the filler cap to the fuel tank and listen inside while your assistant flicks the ignition you should hear it clearly
If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V.
You should be getting around 3 bar measured at the injector rail check to see if the plugs are getting wet indicating fuel is flowing – if not and the injectors are opening then there’s a problem with the pump or the filter or even the pressure regulator

Could also be incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will never add the 'cold start' extra fuel required if the car starts OK when warm then I 'd look into changing the sensor.

Customer: replied 8 months ago.
Mate you are coming up with complatley different answers
You sound like you haven't even read what I've ben writing in the description
Expert:  Matt replied 8 months ago.


Ok to summarize then

there's no sparks

there is ECU power

there is a crank speed signal

there's no injector signal?

does the fuel pump run?

If these too are not present then I'd say that either there's a wiring fault or the ECU is faulty