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j_cst_10

04-13-2022 02:31 PM

Exhaust flapper

1 Attachment(s)

Hey guys, I have a question. I just purchased an 85 K2500 GMC with the factory 350 and noticed it has the exhaust flapper/close off to aid in warm up on the passenger side still attached.

There looks like a vacuum diaphragm that pulls the flapper however I have no hose going to it. Or is some sort of spring that loosens up when heated sort of like a choke on a carb?

Which way allows the exhaust to freely flow? Pulled in or resting?

truckin 79

04-13-2022 05:35 PM

Re: Exhaust flapper

When vacuum is applied flapper is closed, the vacuum hose usually runs from a thermal vacuum switch. No vacuum and the flapper is open so it is fine without a vacuum hose hooked up to it.

j_cst_10

04-14-2022 08:30 AM

Re: Exhaust flapper

Thanks for the reply. I figured it wouldn't make a whole lot of sense for it to close at zero vacuum such as a wide open throttle scenario, but wanted to make sure I wasn't missing anything.

Loco83

04-15-2022 07:18 PM

Re: Exhaust flapper

1 Attachment(s)

Don't know if this will help, this is the diagram off my 83 305 showing the EFE valve vacuum line. :smoke:

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