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  #1  
Old 02-01-2004, 10:29 AM
1988 300sel
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small hose coming off breather to valve cover-where does it go

On a 1988 300sel there is a small hose coming off on the big hose connecting the breather housing to the valve cover. I'm a perty good mechanic and for life of me can't find where this hose connects too. Have ordered a service manuel but have not got it yet. What is this small hose for.
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  #2  
Old 02-01-2004, 12:12 PM
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Location: Southern California
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It's the fuel pressure regulator pressure referenece. It is routed to the PCV system in case the regulator ever starts to seep.

It's common for this nylon line to become brittle and break. It can be replaced or spliced with a short piece of 1/8" vacuum line hose.

Duke
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Old 02-01-2004, 12:19 PM
1988 300sel
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Duke, thanks for the reply. Where is the psv system located
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Old 02-01-2004, 01:52 PM
1988 300sel
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Hey, I found it. What this being hooked back up do to help it . It was hard to start. Will this help that?
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  #5  
Old 02-02-2004, 12:59 AM
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The PCV (positive crankcase ventilation) system draws filtered air from the air cleaner and routes it into the engine. (This PCV inlet hose also is the terminus for the small nylon pressure reference line for the fuel pressure regulator.)

The air circulates throughout the crankcase and blends with blowby gas and is then drawn out of the engine on the small PCV hose that routes to the inlet manifold. This way blowby gases are consumed in combustion. All cars sold in the US have required such systems since 1963 (1961 in CA).

A normal engine inspection (such as during a 15K of 30K mile service) should include inspecting all hoses - coolant, vacuum, PCV, and fuel.

Duke
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Old 02-02-2004, 01:16 AM
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I think it's the FPR you're looking for since you claim the small hose is attached to the big hose. The FPR is ahead of the air meter housing. The hose goes into a stub of rubber hose on the FPR. It goes in from passenger side to driver side just about horizontally. Pull the air cleaner and it'll all make sense.

Sixto
95 S420
87 300SDL
91 300SE (sold)
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Old 02-02-2004, 06:48 PM
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Quote:
Originally posted by 1988 300sel
Hey, I found it. What this being hooked back up do to help it . It was hard to start. Will this help that?
Not likely. Unfiltered air entering the breather system is the main effect, and that will not change the way the engine behaves, in the short term.

Steve
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Old 02-11-2004, 05:51 PM
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Quote:
Originally posted by Duke2.6
It's the fuel pressure regulator pressure referenece. It is routed to the PCV system in case the regulator ever starts to seep.
Duke
Aha! I saw that on my '81 280SE and thought it couldn't possibly be right. I guess it is right after all. Thanks.
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