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  #1  
Old 04-23-2010, 06:20 PM
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Fuel Shutoff Solenoid- How Much Vacuum?

My `83 TD wont shutoff with the key. I have vacuum from the key switch to the fuel shutoff solenoid on the IP. I measure about 3 inches of vacuum from the switch vacuum line to the shutoff with the key switch in the off position. When I connect my vacuum hand pump to the shutoff line , it takes about 5-6 inches to shut the engine down. There is no oil in the shutoff valve line and it holds the vacuum fine. I guess my question is is the vacuum from the key switch less than specs (I know it is less than what this valve needs) or is the shutoff valve requiring more vacuum than it should to shut down the engine (possible sticky or binding valve shutoff valve)? Thanks!!

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Old 04-23-2010, 07:18 PM
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Depending upon your altitude your vacuum system should be reading around 20 inches. You're way low. Test it at the pump. You probably have a leak somewhere.
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Old 04-23-2010, 07:59 PM
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i agree ,you need to check that your getting at least 20 inches of vacume from pump before going further in search.if the pump is ok then go and check the rest of system.
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Old 04-24-2010, 11:38 AM
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You are right

Thanks for the responses. You guys nailed it. I`m getting a solid 20 inches out of the pump (it should- I rebuilt it). At the taps on the line from the pump to the booster I get like 5 inches. I think the check valve in the booster line that the 2 vacuum taps come off of is clogged or bad. Thanks again.
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Old 04-24-2010, 02:11 PM
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Most of the minor vacuum lines on my '85 300D are cracked and split. ALL of mine are going to be replaced as I start working under the hood.

Vacuum hose is sure cheap too.
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Old 04-24-2010, 03:38 PM
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When I dosconnected the Brown Vac Tubing from the Vacuum Shutoff on the IP on my Car 1 month ago and hooked up a Vac Gauge I got 20 inches when the key was turned to the shutoff position.
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Old 04-24-2010, 03:45 PM
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If your Vacuum Pump is good and you have no other Vacuum Leaks:

This is the other Vacuum Switch on your Steering Wheel Lock. The hoses there could be leaking or the Switch Itself could be bad.
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Fuel Shutoff Solenoid- How Much Vacuum?-ignition-switch-x.jpg  
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Old 04-24-2010, 09:13 PM
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are you having trouble with doors locking ,hard brakes etc,maybe booster line is cracked or maybe booster is leaking off vacume,i just went through my vac system to track down leak,start with biggest suspects first then narrow down by system.it can be tedious but do a search here for vacume shuttoff there is a nice diagram there of the whole system.

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