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  #1   IP: 138.207.177.95
Old 07-05-2021, 05:54 PM
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Great Results So Far with Vapor Purge Line

I plumbed in a return line from the fuel pump output back to the tank. It runs through a valve that is just *barely* cracked.
So far so good - fuel pressure is rock steady
What used to happen after a long time running on a hot day is the fuel pressure would get erratic, dropping to 0 or close and bouncing back up to 4. On rare occasion fuel would quit feeding altogether
One odd side effect is the engine is a lot easier to start. I think the carb primes a lot faster now.
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Old 07-05-2021, 06:39 PM
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Joe-
Assuming a Facet pump...
Have you noticed any difference in the temp of the pump?
Maybe running cooler?

(Neil knows where this is going)
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Old 07-05-2021, 07:09 PM
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I did not measure the before and after temp. I am assuming it is at least a little bit cooler. If I cracked the valve more it would probably be a lot cooler.
edit - My buddies old 67 Corvette has this same system with a tiny drilled hole to meter the return fuel.

Last edited by joe_db; 07-05-2021 at 07:14 PM.
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Old 07-23-2021, 07:48 AM
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Update - still no sign at all of vapor lock and the engine remains easier to start
My theory on starting is with my habit of running the fuel out at the end of the day, the vapor return allows the carb to prime again much easier.

I am thinking the fuel pump will also live a longer life being kept a bit cooler.
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  #5   IP: 138.207.177.95
Old 09-10-2021, 08:58 AM
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Still working well. We ran for several hours at 100% power and not a hint of fuel pressure fluctuations. I wish I had done this years ago!

* general hint, many "A4 problems" are not specific to the A4, many a diesel has fuel feed problems and exhaust problems too
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