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997.2 increasingly slow starts

 
Old 05-14-2019, 04:38 PM
  #31  
dfdolan
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Thanks for suggesting this and it's a good lesson that I shouldn't trust a test that I haven't replicated a couple of times to verify. I just repeated the test to cycle on the electrical system, wait 15 seconds, turn it off, wait 10 seconds and try to start. When I tried this over the weekend it seemed to really isolate and exacerbate the slow start and the engine cranked 8-9 seconds, struggled to life, stalled, then started.

This time, it wasn't as labored and still cranked ~4 seconds but fired up without the stumbling, combustion issues that it had over the weekend with this test. So, I would say cycling on the electrical in this test really doesn't impact the issue, which sounds consistent with losing pressure between the HPFP and LPFP.
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Old 05-14-2019, 07:52 PM
  #32  
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OP, are you seeing Check Engine light, and if so have you used an OBD scan tool to check for fault codes?
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Old 05-14-2019, 09:39 PM
  #33  
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Could it be your starter?
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Old 05-15-2019, 09:43 AM
  #34  
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No warning or error lights at all.
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Old 05-15-2019, 09:45 AM
  #35  
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The starter cranks the engine like a jackhammer. There doesn't seem to be any problem with juice and effectiveness cranking the engine.
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Old 05-15-2019, 10:14 AM
  #36  
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I had a direct injected BMW 3.0 L in a 2012 model 335is that developed a slow-to-start problem. Dealer replaced all injectors under warranty, problem gone.
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Old 05-15-2019, 06:57 PM
  #37  
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Originally Posted by dfdolan View Post
No warning or error lights at all.
Have you had the car scanned for any stored fault codes? You can use a simple scan tool or a more sophisticated one like iCarsoft, Schwaben, Durametric. Have you been using any fuel injector cleaner? These DI injectors are very small and sensitive to any deposits as the tips are right there exposed to the high temps in the cylinders. Your situation's a stumper, as you say no Check Engine light. I have an '09 C2 with 41k miles and it leaps to life when asked.
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Old 05-15-2019, 08:14 PM
  #38  
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My Porsche Dealer did a lot of tests for the issue about 6 months ago when they replaced the battery because they couldn't find anything else wrong, and they did find some electrical issue that could be implicated in the slow start symptom. I was skeptical since it absolutely does not seem like any issue with the power to the starter or the starter and the car cranks like a jackhammer. It just used to start in < 1 second and over the past 1.5 years has gone to 6-7 seconds when its sat for a day or more.

I presume they scanned it in their exploration but don't really know and will be asking a lot more questions next visit. I have not done anything to clean the fuel injectors beyond all the scheduled maintenance and service.

The most likely response so far sounds like there is a slow leak allowing the connector between the HPFP and LPFP to lose prime as it sits over time. Once it starts it runs fine so both HPFP and LPFP seem like they have to be pumping just fine.
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Old 05-15-2019, 09:11 PM
  #39  
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Nah, there's no leak between fuel tank and HPFP. If there were you'd smell it. There's no "prime" between low-pressure side and the HPFP. When energized the LPFP turns on for 3 seconds then delivery rate is controlled by voltage from the DME. The LPFP supplies fuel to the HPFP at a constant 5.0 bar. Where do you live and what kind of fuel do you use? For interim my recommendation is to run some injector cleaner with next few tanks. Lots of products out there - Techron, LubriMoly, others. I use AMSOIL P.i.
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