HELP! Runs perfect then just dies! (RESOLVED!)

[RF_Burns]

My coach came with a nice but not installed oak dash inlay. Since the OEM plastic one was pretty scruffy looking, I installed the oak one. Now I have
no labels on my switches. So I don't think of Main/Aux tanks, its just one tank or the other one, or more importantly front/rear tank. Whichever one
has more than 1/2 tank is the one I run on. When I get down to 1/2 tank, that's when I start looking to refuel (and I need a pee break myself
anyway).

If you haven't studied the effects of up/down hills and braking on the GMC, goto

http://bdub.net/gmcmotorhome.info/tank.html

Worst case is braking going downhill.... if you are under 3/4 tank you could easily empty the rear (main) tank into the front (Aux) tank.

We had a club member and long-time owner run out of gas coming down the hill into Watkins Glen NY. He had lots of gas, but it was all in the front
tank. He also did not have an auxiliary brake vacuum pump so he had no brakes either! The light at the bottom of the hill changed just in time for
him to roll right through.

You may want to read up on the brake vacuum pump upgrade:

http://bdub.net/gmcmotorhome.info/addens.html

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[tyler]

The linked gas tank pictures can help in multiple real world scenarios and expectations.

The other opportunity this could have presented (I think your success negates this, so for others in the future maybe) is to test the two tanks
(main/aux) switch. Common failures are the electromechanical switch fails 1) to switch or 2) to seal as it switches and you get air leakage so fuel
pump can't draw. If your configuration is stock, and you had 20 gallons in one tank, a throw of the switch would potentially validate its operation.
Congrats on victory!
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[Joe Weir]

I wonder how much this problem surfaced when new. Imagine spending the princely sums these things were fetching new, only to have it dead in the
driveway.

Would there be a forgotten GM service bulletin? Fascinated about what we constantly re-discover on these coaches as the years go by.
--
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen
guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.

 

[Jim Hupy]

It didn't happen as frequently when these Coaches were not all 40 years
old.
Think back to when you were 17 or 18. Did your back or knees respond
to changes of Barometric pressure back then? I think not. 40 year old
printed circuitry is amazingly durable, considering the number of
repetitive events they have performed in 40 years. In the BILLIONS for
sure. Stuff made today does NOT HAVE the same engineering purposes as the
stuff engineered in the 60's for use in the 70's.
There is a little touch of "planned obsolescence " in everything
around us today. This electronic "stuff" is engineered to last just a bit
longer than the contract payments do. It is intentional, by design.
Fact of life is that spark plug gaps open up with use. Plastic parts
outgas their stabilizing agents from exposure to sun and the elements. Crap
wears out.
Jim Hupy
Salem, Oregon

On Thu, Mar 12, 2020, 8:05 AM Joe Weir via Gmclist
wrote:

> I wonder how much this problem surfaced when new. Imagine spending the
> princely sums these things were fetching new, only to have it dead in the
> driveway.
>
> Would there be a forgotten GM service bulletin? Fascinated about what we
> constantly re-discover on these coaches as the years go by.
> --
> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
> Coachmen
> guys were really thinking about us second hand owners by including that
> beverage center...
> Columbia, SC.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[jim miller]

> The linked gas tank pictures can help in multiple real world scenarios and expectations.

Yes…except that those pictures are grossly incorrect and horribly misleading for two reasons.

1: In actuality the common filler tube is well ABOVE the centerline of the tanks which makes a big difference when considering which circumstances can move fuel inventory between the tanks.

2: the angles shown in the pictures are grossly exaggerated from anything a coach would ever see on the road - unless it were careening down the side of a cliff. The pictures show a tilt angle of perhaps 30 degrees when in actuality a coach would never see more than 10 degrees even in the worst possible hill climb or descent.

I wish someone would correct those pictures as they mislead many people and have been doing so for a long time.

—Jim

Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH