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72T won't start when hot?
Hello All,
Just wanted to reach out to the forum to see if this is common or if its happened to anyone before? Every once and awhile after a spirited drive for about a half hr or so I shut the car off for some reason (today it was to fuel up) and then when I try starting her and she won't. It turns over alright but just does not start. I then open up the engine lid and wait about 1/2 hr till she cools off and she starts right up again! What gives?? tx in advance, Joe |
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08-02-2015, 09:21 AM
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Off hand, sounds like classic case of 'vapor lock.' Is this car
'stock,' or are there fuel system mods?
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John Original Owner 1973 911T. Webers, SSI, SAW & Polybronze, Carrera chain tensioners, 'A' calipers |
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08-02-2015, 09:47 AM
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Have you tried a shot of ether/kwik start in this situation? Direct into the intake(s). Then crank.
If no start, with the ether, consider a failing coil or connections including the infamous green wire. Heat does weird things.
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1983/3.6, backdate to long hood 2012 ML350 3.0 Turbo Diesel |
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08-02-2015, 10:28 AM
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Missing spark or fuel.... as others said if a squirt of starter fluid or brake cleaner helps its vapor lock.
Another possibility is the engine heat causes the Bosch CDI to fail when the temperature spikes in the engine bay right after shutdown. Ingo
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1974 Targa 3.6, 2001 C4 (sold), 2019 GT3RS, 2000 ML430 I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs Porsche "Hammer" or Porsche PST2, PIWIS III - I can help!! How about a NoBadDays DualChip for 964 or '95 993 |
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08-02-2015, 10:35 AM
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Thank you guys,
The car is basically stock with no fuel mods to my knowledge. It does have a MSD ignition mod though. Could that be the issue?? Kind regards, Joe |
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08-03-2015, 06:18 AM
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What I would do then is get it hot and have an engine
timing light handy. If it does not start, check to see if you have a decent spark. If you have spark, it's your fuel, or lack of it. You say the car is stock... Do you have Mechanical Fuel Injection? I never had a fuel supply issue with my MFI 1973 911T, but then I only ran MFI for about 8 years...
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John Original Owner 1973 911T. Webers, SSI, SAW & Polybronze, Carrera chain tensioners, 'A' calipers |
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08-03-2015, 07:25 AM
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Hi John,
Yes it's MFI. Starts right up when cold though. I will try some of the suggestions. thank you all. |
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08-03-2015, 03:49 PM
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If its MFI then make sure the cold start solenoid is operating correctly (ie, not at all once the engine is warm) Easy enough to slip the wire off the solenoid for a few trial starts.
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1972 911T Coupe with a '73E MFI engine and 'S' pistons 10 year resto mostly completed, in original Albert Blue. ***If only I didn't know now what I didn't know then*** |
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08-03-2015, 11:47 PM
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Like stated above, use ether as a test, I bet it starts.
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72 911 Although it is done at the moment, it will never be finished. |
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08-04-2015, 04:25 AM
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Join Date: May 2007
Location: Redmond, Washington
Posts: 47
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I have had the exact same problem with my 72T. I attribute it to vapor lock. It really became a problem when I would run into the store for a few minutes and come back out and it would not start. I addressed it by running an extra circuit to the fuel pump. When I turn the car off for a short time, I turn the fuel pump on and keep the circuit pressurized. This extra pressure stops the fuel from vaporizing. I haven't figured out a permanent fix yet.
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08-04-2015, 05:44 PM
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Da cab
1974 Porsche 911 Targa 3.6
1972 Porsche 911T
Tobluforu
