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78sc's Avatar
 
Join Date: Dec 2003
Location: Bartlesville, OK
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Backfire, then no start

Hi all,

It's been a while since I've been driving my 911 or been around these forums. Thought I'd ask you all a question as I get back into enjoying these 911's we like so much.

So, I got mine running again and had been driving it for about a week. One morning last week, I went to start it and it backfired pretty good and then would not start. If I let it sit for a couple of minutes, and tried again it would try to start but then just crank. All these attemps to start were with my foot off the gas pedal. So I took my non-fun car to work and when I got home again, all it does is crank and not even a hint of wanting to fire.

My question is, where do you guys think I should start the troubleshooting? The airbox has a pop-off valve installed. I can't see any cracks in the airbox, but I'm sure there is a lot I can't see with just the airfilter cover removed.

Thanks.

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Phil
1978 911 SC
Old 06-10-2013, 10:08 AM
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Is the pop off valve seated on its o-ring properly?
Basic tune up of ignition and check fuel pressures would be next, spark plugs fouled?
Old 06-10-2013, 10:24 AM
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Check to make sure that you are getting spark. If so then .... check for vacuum leaks etc.

I had a similar occurrence, and after the backfile got no spark, turned out the "coil" inside the distributor had failed. That is "green" wire related.

Just a thought.

Jay
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Old 06-10-2013, 10:25 AM
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Something has cracked/broken off, and now you have a big vacuum leak that is preventing the car from starting.
Old 06-10-2013, 10:27 AM
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Pop off valve or broken air box.
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Old 06-10-2013, 11:03 AM
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If you pop off valve popped completely off like mine did remove the air filter and you will see it unsecured. Clean out old glue or adhesive and mix a 2 part epoxy and reseat the valve and you should be good to go
Old 06-10-2013, 11:07 AM
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Thanks for the thoughts guys. I will go hunting for the culprit tonight.
Old 06-10-2013, 11:43 AM
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So, I checked spark, that was good. Plugs were not fouled. Couldn't find any hoses that got blown off or any cracks that might cause a vacuum leak. Then realized I couldn't hear the fuel pump. Turned out the fuse was blown. Weird! Replaced that and it started right up.
Old 06-11-2013, 08:16 AM
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Good find, and thanks for updating with your results.
Now go drive it like you stole it!
Old 06-11-2013, 08:34 AM
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arry911
 
Join Date: Nov 2011
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Quote:
Originally Posted by 78sc View Post
So, I checked spark, that was good. Plugs were not fouled. Couldn't find any hoses that got blown off or any cracks that might cause a vacuum leak. Then realized I couldn't hear the fuel pump. Turned out the fuse was blown. Weird! Replaced that and it started right up.
I had similar problem the other day turned out the fuse was corroded not even blown, Just put in new fuse and it started.
Old 06-12-2013, 07:30 AM
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Coil failure.
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Old 06-12-2013, 07:53 AM
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Quote:
Originally Posted by Jim Richards View Post
Coil failure.
Hi Jim...sorry, not quite sure what you mean.

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1978 911 SC
Old 06-12-2013, 08:46 AM
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