Art,
Where are you in Alabama (I was born in Troy)? You need to join the GMC
Dixielanders -- we had a rally at Noccalula Falls two weeks ago; we could
have met there!
Re: Vapor lock. I can honestly say that in 20 years of GMC ownership, all
of it while living in GA, but travelling everywhere from Key West to
Fairbanks, I've never had vapor lock. I thought I did a couple of times,
but subsequent troubleshooting found true problems. I tell you all that so
perhaps you'll consider some of my mods to be worth considering. Remember
that these occurred progressively since 30 Apr 1998. Also, ALL of it
depends upon clean fuel tanks, good filters, and new fuel lines.
My first upgrade to the fuel system was made in preparation for the trip
for which I originally bought the coach: A trip to Alaska. Anticipating
the vapor lock I'd experienced in the western mountains with other
vehicles, I installed an electric pump, immediately downstream of the
selector valve. Its output was plumbed directly to a tee at the input to
the carburetor. I would NEVER run an electric pump in series with a
mechanical pump. Two reasons for that: 1. The possibly excessive
pressure you're seeing. 2. Even more importantly, the possibility of a
failed diaphragm in the mechanical pump allowing the electric pump to fill
the crankcase with gasoline.
As it turned out, that was not a good arrangement -- I counted on the
output valve in the mechanical pump to act as a check valve for the
electric pump when it was in use. In Yellowstone NP, the top gasket on the
mechanical pump failed, allowing either pump's output to dump straight out
on the ground. Luckily I caught it early and had parts to correct it.
My most important upgrade to the GMC's fuel system was elimination of the
tank selector valve and replacement of the mechanical pump with an electric
pump for each tank, mounted immediately forward of the Aux tank and tee'd
together with check valves into the rear-to-front fuel line. That
improvement alone eliminates the ethanol-sensitive valve and provides the
needed pressurization of most of the fuel line. It should prevent most
vapor lock.
Perhaps an under-rated reason for my vapor-lock free life is the "surge
tank" I installed. That's a 12" section of 10" diameter, 1/4"+ thick
aluminum tubing with caps/mounting feet welded on each end. That tank is
equipped with a fuel inlet (fed by the selected electric pump), a fuel
outlet for a return line to the drain fitting on the Aux tank, and a fuel
outlet to the carburetor (now to the EFI's high pressure pump). It also
has a port into which the return line from the EFI's throttle body is
plumbed. That tank is mounted beneath the step riser under the driver's
seat, a free space that's protected from high temperature air by the wheel
well liner.
The surge tank provides the engine with a source of fuel which is always
purged of vapor; generally, any vapor lock in the rear-to-front line will
be evacuated before that I have had trouble with vapor lock and the generator quits if I have been
> driving for a while. I have one muffler sitting across the bottom and a
> little lower than the two mufflers that came out. Vapor lock has been a
> problem if I’m driving with the out side temperature above 85F. Living in
> Alabama that makes for problems. I been trying different things to fix the
> vapor lock. I installed a electric pump in series with the mechanical fuel
> pump. The electrical is where it will not get hot and still vapor locks.
> I turn on the electrical pump when it is needed. I do not like to run both
> pumps and fuel pressure goes up to 9 PSI. I worry about the float not
> holding 9 PSI. I heard of to many fires on these old RV’s. I checked mine
> an it seems to work fine at 9 PSI but I am not comfortable at that pressure
> although I have run some at that pressure when having vapor lock problems.
>
> Art
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
