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Registered
Join Date: Jul 2005
Location: cairns Australia
Posts: 12
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help cold starting
some help please with my 911 84 3.2L US spec carrera, the car doesn't start well, 3 or 4 cranks are needed while depressing pedal about 1/3 then it hunts before settling at 1200rpm.
Clues:- 1. The car runs 100% fine once it starts 2. Hot starts are better but not perfect 3. The head temp sensor ( old type ) checks out resistance wise 4. Idle position switches check out OK 5. Cleaned every earth / contact concerned with DME 6. Car has no catalyst in converter but has an O2 sensor (do I need it ? ) but dont think this affects start up 7. Idle valve gets its 12v and opens 3mm on ignition 8. car wont start at all with head temp sensor disconnected The only thing I can find wrong is the head temp reference voltage at Pin13 DME is 4.3V instead of 5.0v could this be enough ? any way to tweak it up ? the guy with the correct answers wins a free holiday to Australia and a night with the barmaid of his choice at the local pub ! thanks in advance guys |
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07-12-2005, 05:33 PM
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Join Date: Mar 2004
Location: S.E. Pennsylvania
Posts: 1,967
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May be the check valve on the fuel pump not allowing fuel to remain in the lines.
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The Fox Carrera |
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07-12-2005, 05:42 PM
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Location: cairns Australia
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how do I check this pls ?
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07-12-2005, 07:36 PM
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Location: S.E. Pennsylvania
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Have a friend clamp off the rubber fuel line to stop the flow of fuel on the engine side of the fuel pump, right when you turn off the engine. Wait about 20 minutes, have your friend remove the clamp and immediately try to start your car. If it starts right away, it's the check valve that's faulty.
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07-12-2005, 07:46 PM
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Join Date: Dec 2004
Location: Novato, CA
Posts: 3,064
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I'm no Motronic expert, but with CIS if the check valve is gone, it will affect hot starts, not cold starts...
ianc
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BMW 135i. Nice. Fast. But no 911... "I will tell you there is a big difference between driving money and driving blood, sweat and tears." - PorscheGuy79 |
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07-12-2005, 08:56 PM
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Join Date: Jul 2005
Location: cairns Australia
Posts: 12
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Have done the check valve test as you suggested, it fired then stopped 3 times. Not sure what we've proved here as the car didn't start well anyway. Maybe I need the fuel pressure rig to test this conclusively. The only thing that inputs the DME that I haven't tested is the air flow sensor but surely if this we're duff it wouldn't run as well as it does. Does anyone have any more ideas before I give up and take it to Porsche. Is the 4.3V critical instead of 5v does anyone know to the temp sensor ( this is on the o/p pin of the DME ) ???
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07-14-2005, 08:36 PM
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Join Date: Dec 2004
Location: Novato, CA
Posts: 3,064
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Dave,
Since I own a CIS rig and not DME, I'm afraid I'm out of my league on this one. I would suggest you do some searches here though or wait for someone to chime in. I will give 99.99% chances that the solution to your problem can be found here with a little diligence. Or, go to Porsche.  ianc
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BMW 135i. Nice. Fast. But no 911... "I will tell you there is a big difference between driving money and driving blood, sweat and tears." - PorscheGuy79 |
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07-14-2005, 10:53 PM
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Join Date: Mar 2004
Location: S.E. Pennsylvania
Posts: 1,967
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By checking the valve...it tells you whether or not fuel is remaining in the lines. If the fuel is returning past the check valve, you will crank and crank until those lines fill again and start the car.
ON the head temp sensor. you mention that it will not start at all with it disconnected. A quick test is: while engine is running, disconnect the sensor from the rail and your engine should race.
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The Fox Carrera |
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07-15-2005, 12:36 AM
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