air cleaner sensor leaks

J

jack christensen1

New member
Mar 30, 2008
264
0
0
I'm tracking down vacuum leaks on my 455.

The flap that allows warm air from the manifold to get to the carb and help during startup is controlled by a sensor mounted in the air cleaner assy.

I found that the sensor seems to work properly in that when the engine is cold, vacuum passes to the flap controller and operates it causing warm air
to enter the engine. What I also found was that when the sensor warms up it does cause the flap to release as it should, but the sensor then leaks
vacuum when it's warm. It's not a whole lot, but more than I would have expected. I would expect it seal off the vacuum. Is this usual or is the
sensor bad?
--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
 
If it were me, I would render the thermactor inactive in the wide open
position and eliminate the vacuum line and potential leak. We use these
coaches pretty much in the summer season, so that air cleaner flap is of
little value. Jwiwd.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

I'm tracking down vacuum leaks on my 455.

The flap that allows warm air from the manifold to get to the carb and help
during startup is controlled by a sensor mounted in the air cleaner assy.

I found that the sensor seems to work properly in that when the engine is
cold, vacuum passes to the flap controller and operates it causing warm air
to enter the engine. What I also found was that when the sensor warms up
it does cause the flap to release as it should, but the sensor then leaks
vacuum when it's warm. It's not a whole lot, but more than I would have
expected. I would expect it seal off the vacuum. Is this usual or is the
sensor bad?
--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Jim, he's in Cal. and has a 76. It needs to work (at least look like it) every 2 years for our bi-annual emissions check.
Wish I could have made it to Paso to meet all of y'all.


> If it were me, I would render the thermactor inactive in the wide open
> position and eliminate the vacuum line and potential leak. We use these
> coaches pretty much in the summer season, so that air cleaner flap is of
> little value. Jwiwd.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>

>
> I'm tracking down vacuum leaks on my 455.
>
> The flap that allows warm air from the manifold to get to the carb and help
> during startup is controlled by a sensor mounted in the air cleaner assy.
>
>
> I found that the sensor seems to work properly in that when the engine is
> cold, vacuum passes to the flap controller and operates it causing warm air
> to enter the engine. What I also found was that when the sensor warms up
> it does cause the flap to release as it should, but the sensor then leaks
> vacuum when it's warm. It's not a whole lot, but more than I would have
> expected. I would expect it seal off the vacuum. Is this usual or is the
> sensor bad?
> --
> Jack Christensen - K6ROW,
> '76 Glenbrook/Clasco - "The Silver Bullet",
> Sebastopol, CA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Patti & Jerry Burt
73 Gmc 26' Canyon Lands -
77 Palm Beach
Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers
 
Jim, I doubt it is supposed to leak. If you need one I've got one I'll send you.
--
Patti & Jerry Burt
73 Gmc 26' Canyon Lands -
77 Palm Beach
Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers
 
Sorry you live in California. I didn't think about emissions testing there.
If it was so equipped and sold as a California vehicle, then it has to be
in place and functional when emissions testing is performed. DON'T KNOW
ABOUT FIVE MINUTES LATER. 'EH'. I've been hanging out with some Canadians
lately.
Jim Hupy
Salem, Or ( we don't have emissions testing in this airshed, but, do in
Portland and Medford)

Jim, he's in Cal. and has a 76. It needs to work (at least look like it)
every 2 years for our bi-annual emissions check.
Wish I could have made it to Paso to meet all of y'all.

> If it were me, I would render the thermactor inactive in the wide open
> position and eliminate the vacuum line and potential leak. We use these
> coaches pretty much in the summer season, so that air cleaner flap is of
> little value. Jwiwd.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>

>
> I'm tracking down vacuum leaks on my 455.
>
> The flap that allows warm air from the manifold to get to the carb and
help
> during startup is controlled by a sensor mounted in the air cleaner assy.
>
>
> I found that the sensor seems to work properly in that when the engine is
> cold, vacuum passes to the flap controller and operates it causing warm
air
> to enter the engine. What I also found was that when the sensor warms up
> it does cause the flap to release as it should, but the sensor then leaks
> vacuum when it's warm. It's not a whole lot, but more than I would have
> expected. I would expect it seal off the vacuum. Is this usual or is
the
> sensor bad?
> --
> Jack Christensen - K6ROW,
> '76 Glenbrook/Clasco - "The Silver Bullet",
> Sebastopol, CA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Patti & Jerry Burt
73 Gmc 26' Canyon Lands -
77 Palm Beach
Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Thanks all,
I like Jim's suggestion. I've never had anyone during the smog check do more than look to see if the hose to the manifold was present. No test of
the device. I'm devious enough to make it look like everything is OK.
--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
 
The stove defaults to no vacuum - closed. A simple fix.

> Thanks all,
> I like Jim's suggestion. I've never had anyone during the smog check do more than look to see if the hose to the manifold was present. No test
> of the device. I'm devious enough to make it look like everything is OK.

--
Patti & Jerry Burt
73 Gmc 26' Canyon Lands -
77 Palm Beach
Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers
 
You mean a fix about the size of a BB? :-)

Ken H.

> The stove defaults to no vacuum - closed. A simple fix.
>
>

> > Thanks all,
> > I like Jim's suggestion. I've never had anyone during the smog check do
> more than look to see if the hose to the manifold was present. No test
> > of the device. I'm devious enough to make it look like everything is OK.
>
>
> --
> Patti & Jerry Burt
> 73 Gmc 26' Canyon Lands -
> 77 Palm Beach
> Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Yup!
Jim Hupy

> You mean a fix about the size of a BB? :-)
>
> Ken H.
>
>

>
> > The stove defaults to no vacuum - closed. A simple fix.
> >
> >

> > > Thanks all,
> > > I like Jim's suggestion. I've never had anyone during the smog check
> do
> > more than look to see if the hose to the manifold was present. No test
> > > of the device. I'm devious enough to make it look like everything is
> OK.
> >
> >
> > --
> > Patti & Jerry Burt
> > 73 Gmc 26' Canyon Lands -
> > 77 Palm Beach
> > Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Wrong. No vacuum signal is open by return spring (cold air)
Vacuum moves the door against spring tension to closed (hot air from manifold stove)
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
The way I see it, the stove is open when supplying heat. So, I would suggest closed when vacuum is removed. It's all good.
Either way, Jack, kill the vacuum and you're good.

> Wrong. No vacuum signal is open by return spring (cold air)
> Vacuum moves the door against spring tension to closed (hot air from manifold stove)

--
Patti & Jerry Burt
73 Gmc 26' Canyon Lands -
77 Palm Beach
Members: FMCA - GMCMI - GMCWS - Pacific Cruisers - 49ers
 
Jack, for the CA smog test the vacuum motor and temp sensor is just a visual inspection. My vacuum motor leaked so I blocked the vacuum source so
that there was always cold air to the intake. On our trip to Alaska there were some cold mornings where it would take awhile to warm up so I decided
to repair the system. I replaced the vacuum motor and the temp sensor so it works as designed. When the temp sensor is warm and the vacuum motor is in
cold air intake position the temp sensor does leak a small amount of air into the vacuum source. There is a restriction in temp sensor to limit the
air flow and because the sensor is in an area of lower pressure the amount of vacuum loss is insignificant.
--
1977 Palm Beach
TZE167V100274
 
You must log in or register to reply here.
Get your shine on at www.cruzingear.co
GMCMI Fall 2026 Rally

Share this page

Share this page
Top Bottom
Back