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Old 07-08-2017, 10:30 PM   #1
ericn1300
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92 Bravada vapor locking

Sylvester, our 1992 Bravada, has been known for vapor locks in the fuel rail when using E-85 gas on hot days, especially after a short stop on a hot engine.

My daughter knows better and only uses non-ethanol fuel in the summer but today she called me for a no start condition on a cold start. It was sitting in full sun at 105 degrees and 6% humidity, so really not that cold of a start, just the first start of the day.

I had her rock the key from off to run position for a count of three a few times without cranking the engine and that broke the vapor lock.
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Old 07-09-2017, 09:40 AM   #2
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Re: 92 Bravada vapor locking

I'm a bit confused over the correlation drawn between temperature and vapor lock with ethanol and gasoline. It may be a coincidence you have noticed, but the numbers don't really support it.

By the pure physics, ethanol has a lower vapor pressure than gasoline at any liquid temperature below 206F (97C). Further, ethanol had a higher vaporization temperature than gasoline. That's a primary reason that ethanol blends do not vaporize as well as gasoline in cold temperatures. There is a 1994 US EPA study (and white paper) on the evaporation of gasoline and ethanol blends. It makes for interesting reading, and may explain the symptoms you might be experiencing.

If the fuel system is sealed as it is supposed to be (no pressure leaks) the phenomenon should not occur. The pressure control for the EVAP canister and secondary pressure relief of the filler cap should maintain sufficient pressure to prevent vapor lock. That should be checked out. In the interim, running the fuel pump prime cycle several times before starting should purge the lines and fuel rails of vapor and charge them with liquid fuel.
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Old 07-09-2017, 12:42 PM   #3
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Re: 92 Bravada vapor locking

Agree with Blue....no such thing as vapor lock on a fuel injected engine....

YOU ARE NOT SUPPOSE TO BE USING E-85 FUEL
....ONLY "Flex" designated engines are...
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Old 07-09-2017, 08:26 PM   #4
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Re: 92 Bravada vapor locking

Quote:
Originally Posted by ericn1300 View Post
Sylvester, our 1992 Bravada, has been known for vapor locks in the fuel rail when using E-85 gas on hot days, especially after a short stop on a hot engine.

My daughter knows better and only uses non-ethanol fuel in the summer but today she called me for a no start condition on a cold start. It was sitting in full sun at 105 degrees and 6% humidity, so really not that cold of a start, just the first start of the day.

I had her rock the key from off to run position for a count of three a few times without cranking the engine and that broke the vapor lock.
Very good trick, letting the fuel pump prime the system. I've done that when putting my '92 in service so it'll start easier, when the weather cools off.
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