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Date:         Thu, 26 Sep 2002 19:53:18 +0000
Reply-To:     Jfp w/3 WBXs <jfp7@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jfp w/3 WBXs <jfp7@HOTMAIL.COM>
Subject:      Hard hot restarting
Comments: To: jstric01@CS.FIU.EDU
Content-Type: text/plain; format=flowed

Hi Jeff,

I'm certainly no 2.0L aircooled expert as my expertise lies with my 3 2.1L WBXs(for which Stan Wilder thinks I'm an idiot - but that's another story...). However all Bosch fuel injection systems function the same in the following areas:

Upon shut down a one-way check valve closes in the fuel pump outlet.

The fuel pressure regulator lacking vacuum, closes completely.

This action traps fuel under pressure behind the fuel injectors.

This function is called "residual pressure" retention and is designed into the fuel system to counter vapor lock during hot engine restarts.

When a hot engine is shut down, a substantial "heat surge" occurs in the engine compartment.

The residual pressure retention function counters the chance of a hot restart vapor lock by raising the gasoline's boiling point. Almost all cooling systems operate at peak temps above 212*F using trapped system pressure to raise the coolant boiling point.

If the required residual pressure is not held for 30 to 90 minutes, a vapor lock and a labored hot hard restart will occur. over time it's OK for the residual pressure to bleed off as the engine heat soak also bleeds off.

Check the fuel pressure per the Bentley and then shut the engine down and monitor the residual pressure. 1.5 bar to 2 bar would be good.

Also be aware that if the residual pressure is lost in a short time, it may not be a leaking fuel pump outlet check valve or pressure regulator. It could also be a leaking injector which would "wash down" the cylinder walls weakening the piston ring oil seal and causing a compression test to indicate low compression values................

Regards, John

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