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Matt, Engineer - BEng Hons
Category: Porsche
Satisfied Customers: 21991
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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996 cranks, but won't start...I tried a spare key that's

Customer Question

996 cranks, but won't start...I tried a spare key that's new/never used, still won't start. it turns over for as long as key is engaged, but won't stay started...
JA: Can you turn the steering wheel at all? And what about the key? Is it worn or damaged?
Customer: yes, I can turn the steering wheel as normal..I had to have a new key made 4 years ago after wife lost my spare. I keep that "new" unused key in my desk drawer, it's never used, basically brand new.
JA: What is the model/year of your Porsche?
Customer: 2001 996 Carrera 2
JA: Are you fixing your Carrera yourself? What have you tried so far?
Customer: it just happened 2 hours ago. I drove it to the dog park, then when I was ready to come home, it wouldn't start...No, not trying to fix on my own.
JA: Anything else you want the mechanic to know before I connect you?
Customer: oh, I have a mechanic, if it comes that...Rennen performance in Tampa...
Submitted: 1 month ago.
Category: Porsche
Customer: replied 1 month ago.
Due to hurricane here in Tampa, premium octane fuel wasn't available, and 2 days ago, I filled up with low octane gas...could that be the problem? battery seems fine/engine cranks when I turn the key, but it just won't fully start.
Customer: replied 1 month ago.
this has never happened before, I've had the car since 2010.
Expert:  Matt replied 1 month ago.


I doubt the low octane gas is the reason why it won't start

1st check for spark by removing one of the spark plugs and plug it back into its lead 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 (at the other end of the plug lead) 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 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

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

Expert:  Matt replied 26 days ago.

do you still need help?
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