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Old 09-06-2013, 11:20 PM   #1
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Default 4.9L hissing noise after engine shut off?

Hey guys I have a 1983 F150 with 4.9L. Sometimes when I shut off my engine it will make this hissing noise. I have no a/c hooked up so it can't be that. The weird thing is though, when I shut off the engine, the engine turns over one more time and then a hissing noise will follow... Any thoughts on this?
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Old 09-07-2013, 01:03 AM   #2
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Mine does it too. Dunno why. But it dont hurt anything.
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Old 09-07-2013, 12:32 PM   #3
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I have always heard the term "dieseling" when a gas engine runs just a tad after ignition is turned off. Something with the timing is off a bit. Probably retarded a hair. As your motor rotates, it builds compression and still creates a little vacuum. Your probably hearing all the leak down with the key off. Because its not firing and sending it through the exhaust as normal.
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Old 09-08-2013, 05:17 PM   #4
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My 85 bronco does that. It has a 302 FI and I tracked it down brake booster vacuum lines. I replaced alot of the parts and hoes. Still does it.
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Old 09-09-2013, 06:00 PM   #5
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Check for vacuum leaks. If there are none when was your last tune up? It could be timing. I just resolved this issue on my 83 f150 300 with a tune up. I knew the timing was right and there weren't any vacuum leaks though.
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Old 09-09-2013, 11:25 PM   #6
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ya its dieseling, usually caused by overheating and or too advanced timing. check ur timing and check ur coolant/thermostat. did u put special plugs in it like the tri tipped ones? if so, go back to basic, check ur fuel, have you changed grade/brand or started using an additive?
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Old 09-09-2013, 11:27 PM   #7
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its called dieseling cause the motor is still running, only its pure heat and compression that's igniting the fuel, just like in a diesel engine
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Old 09-09-2013, 11:27 PM
 
 
 
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