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Porsche 911 Carrera 4S: 2009 911 c4s. have had long problem

2009 911 c4s. have...
2009 911 c4s. have had long problem with starting. sometimes when you turn the key nothing happens. sometimes, you have to turn the key several times before it starts and then when it starts, it dies immediately and takes several tries to get started. the dealership has replaced fuel pumps and recently the clutch switch during the 4 year service. now, instead of just not starting when the key is turned, the trunk has now opened twice. in the past, after each oil change/service, the mpg indicator has started high and worked its way down. this time, it started low and is working its way up for the first time. dealership says they can't even find a problem.
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Answered in 18 hours by:
10/23/2013
Matt
Matt, Engineer - BEng Hons
Category: Porsche
Satisfied Customers: 22,243
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello

This could be a wiring issue and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensors

Throttle position sensor

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Also replace the spark plugs if any of them fail this checklist:

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

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 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

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Customer reply replied 4 years ago

car is under warranty and dealership changed spark plugs during the 4 year service. there has not ever been a check engine light and the dealership said that there were no stored fault codes in the DME. If I take it back to them, they will again check for fault codes. they don't seem to be able to get the car to fail while it's there.

Hello Brian

one of the reasons for checking the electrical connections is that you can have bad connection or a poor earth that will offset a sensor signal but not enough to make it flag as a fault


So its well worth running through the connections as I've mentioned and I'd also ensure that the smaller wiring loom earth points ( ring terminals) that are bolted to the engine block are in good condition
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Customer reply replied 4 years ago

ran the car back over to the dealership. they have checked everything on your list and checked the car for faults again with no luck. any other suggestions?

Hello Brian

just to confirm the engine cranks / turns over OK?
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Customer reply replied 4 years ago


yes, it is cranking fine at the moment. intermittent starting problems.

Hello Brian

Intermittent faults like this can be very hard to track down as you've found, what I'd suggest is to replace the ECU relay and fuse with new items as I've known relays to stick and fuses to have cracks which only give issues once things are warm

both of these are only a few dollars

also if you can catch it when the problem occurs then 1st check for spark by removing one of the spark plugs and plug it back into its coil and rest it on the metal of the engine ( DO NOT hold it on place by hand) then have your assistant turn the engine over whilst you watch the plug. It should give a fat blue spark at regular intervals.

If not then check that there's power to the coil pack using a meter. If there’s 12V at the pack but no spark then check the ECU power supply (fuse and relay) and also the connections to the crankshaft speed sensor.


If there is a spark and its still not starting then its likely that the ECU isn't opening the fuel injectors, 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 you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel
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Customer reply replied 4 years ago

i just had spark plugs changed and problem occurred both before and after. right after changing, problem was worse for a few days and hood opened twice and then got better. also, my 'mpg' indicator normally starts high after an oil change and works its way down. this time, it started low and worked its way up for the very first time. they did calibrate my fuel gauge and maybe that's why??

Hello Brian

I don't think the plugs are the issue, more likely that the issue is with the ECU (engine control unit) or a sensor thats preventing the ECU from functioning correctly

hence my suggestions of above to try and locate the issue

I wouldn't worry about the hood opening or the mileage gauge as these are secondary to the main issue

As I said your best bet is to try and investigate the issue when it occurs
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Customer reply replied 4 years ago

unfortunately, i'm not a mechanic and i have to take the car to the dealership and when it gets there, they can't seem to replicate the problem. thanks for your help.

Hello Brian

whereabouts in the country are you? As I'll try and locate a specialist as you always get better service from an independent and far better value for money
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Customer reply replied 4 years ago

i'm in memphis, tn. car is still under warranty, so no charges for this work. i have another independent here i used to use, XXXXX XXXXX.

Hello Brian

If the car is still under warranty then I'd see if you could get them to replace the engine bay wiring loom
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Customer reply replied 4 years ago

after they hooked up the car again looking for faults, i now have developed a new problem--the lumbar support in the seat keeps filling up when i'm not driving. still sounds live an electrical problem to me.

Hello Brian

OK these quite random electrical issues ( hood opening , lumbar support moving ) coupled with trouble starting now makes me think that there may be an issue with the BCM ( body control module) as this also controls the immobilser function - which may be cutting in and out

I'd ask the dealer if they can run a diagnostic on this aspect and point out body control issues you've been having
Matt
Matt, Engineer - BEng Hons
Category: Porsche
Satisfied Customers: 22,243
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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