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On Porsche #15
Join Date: Sep 2015
Location: SF Bay Area
Posts: 5
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Constantly Needing Primed
I'm a long time viewer, but just recently signed up. I'm having an issue that I was hoping someone here might be able to shed some light on a solution, or tips to get things in motion.
I have a 1974 911, with a 1981 3.0. The car starts fine, and runs great first thing in the morning with no issues. BUT...Let's say I start it up, drive to the store miles away, that's when things go awry. It seems that once the engine is warm it just turns over, but doesn't want to start. I have discovered that if I pull off the air filter lid and prime it, the car starts right up again. Additional symptoms that are pointing me towards my guess; not all the time, but on occasion, when I'm above 4k rpm it sputters. For a 81 3.0 it also seems that it doesn't have all of the horsepower it should (or maybe it just seems that way because I'm comparing it to my 480hp Dinan BMW). Sound familiar to anyone? Facts: Cold starts fine Warms starts require priming Occasional Pop at high RPMs What I was thinking: Maybe the fuel pump Any help would be appreciated. |
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09-27-2015, 08:27 AM
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Registered
Join Date: Jul 2001
Location: mt. vernon Wa. USA
Posts: 8,740
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[B]Current projects: 69-911.5, Previous:73 911X (off to SanFrancisco/racing in Germany).77 911S (NY), 71E (France/Corsica), 66-912 ( France), 1970 914X (Wisconsin) 76 911S roller..off to Florida/Germany RGruppe #669 http://www.x-faktory.com/ |
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09-27-2015, 08:38 AM
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Join Date: Aug 2013
Posts: 2,123
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The comparison to the Dinan BMW is not quite apples to apples…the warm start issue could be the fuel accumulator or possibly a check valve if that model has one. I had similar symptoms in my 930. I had the check valve and accumulator replaced. Got start issue went away.
Lots of more knowledgeable folks will likely chime in… Good luck. |
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09-27-2015, 08:44 AM
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ROW '78 911 Targa
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First thing you will need is a good CIS fuel pressure gauge set up.
Then you can begin to troubleshoot properly. You need system pressure, cold pressure, Warm pressure and residual pressure readings at a minimum to determine what is going on. Read the CIS for Dummies thread for sure. Post your results of the tests and help will come your way. The last thing you want to do is start throwing parts at it blindly. CIS Troubleshooting for Dummies
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Dennis Euro 1978 SC Targa, SSI's, Dansk 2/1, PMO ITBs, Electric A/C Need a New Wiring Harness? PM or e-mail me. Search for "harnesses" in the classifieds. Last edited by timmy2; 09-27-2015 at 08:56 AM.. |
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09-27-2015, 08:51 AM
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Registered
Join Date: May 2004
Location: Lake Cle Elum - Eastern WA.
Posts: 8,417
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My 73.5 has an engine from a 3.0 with CIS. When I had this exact problem, a new fuel accumulator from PELICAN PARTS solved my problem.
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Bob S. 73.5 911T 1969 911T Coo' pay (one owner) 1960 Mercedes 190SL 1962 XKE Roadster (sold) - 13 motorcycles |
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09-27-2015, 08:52 AM
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Sounds like you're loosing residual fuel pressure. You will need a pressure gauge to trouble shoot the problem.
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Pete 79 911SC RoW "Tornadoes come out of frikkin nowhere. One minute everything is all sunshine and puppies the next thing you know you've got flying cows".- Stomachmonkey |
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09-27-2015, 08:54 AM
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Registered
Join Date: Dec 1999
Location: Novato, CA
Posts: 4,740
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Loosing prime when the engine is warm and the 4k sputter are two different issues that need to be dealt with individually.
Let's start with the prime issue. What your symptoms are pointing to is a lack of prime from the cold start valve which makes you do it manually. You need to find out why you are not getting the cold start valve working during that critical warm period. After your sort that out, work on the sputter issue...one thing at a time! Cheers, Joe |
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09-27-2015, 10:49 AM
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ROW '78 911 Targa
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CSV doesn't fire unless car is cold. When warm restart is troublesome, it is usually due to residual pressure concerns. Let's get some test results before steering in different directions....
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Dennis Euro 1978 SC Targa, SSI's, Dansk 2/1, PMO ITBs, Electric A/C Need a New Wiring Harness? PM or e-mail me. Search for "harnesses" in the classifieds. |
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09-27-2015, 03:23 PM
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Registered
Join Date: Dec 1999
Location: Novato, CA
Posts: 4,740
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Thermal/time switch is stamped 45 degrees C which is actually quite warm to the touch for a cold engine IMHO. The popular misconception is that the cold start valve only operates on a stone cold engine.
Last edited by stlrj; 09-29-2015 at 08:38 AM.. |
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09-28-2015, 05:04 AM
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Heinz
1979 Porsche 911SC
