Vapor lock feedback

L

lw8000

Member
Jul 30, 2012
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Hello all:
I was looking for some additional feedback on vapor lock, mainly what kind of conditions that you have seen it in. We seem to be troubled by it when
temps get up over 83-85 degrees outside, it first started last summer going down the Florida where temps got up to 93+. Since then, we've had an
inline fuel pump and rebuilt carb installed by JimB, that seems to have done the trick for getting around the issue (which only seems to happen when
slowing down or stopping and trying to get going again).
Also since the inline fuel pump, we've had an aluminum ported Offenhauser intake manifold installed, with the Paterson blockoff kit. We had this done
due to cracking of the original manifold. Some thought maybe this would help with vapor lock, however today we again had it happen to us, temps
outside were around 83-84 degrees with full sun, we were on the highway for about 45 minutes after taking off cold. After exiting the highway,
stopping at a sign, and accelerating again on a backroad, after 10 seconds while accelerating the engine starting surging a little bit. After
flipping on the electric aux pump, the surging went away after about 15-20 seconds. We were running the dash AC at the time as well.

Does this seem to be a little bit extreme with it happening when it's 83-84 degrees out, or is this pretty much what everybody else is experiencing?
And is the main fix still just using an aux electric pump back near the tanks? I can't imagine this could be anything else besides vapor lock. Over
the years we've had everything in the fuel system either replaced or fixed: fuel tanks cleaned & coated, new rubber hoses & fuel filter, new solenoid,
new inline fuel pump and fuel system check (by JimB), new Carter mechanical fuel pump, rebuilt carb (from JimB), new aluminum intake, and even a new
fan clutch (Delco 15-4947). Everything seems to be in order.

Feedback, thoughts and anything else is more than welcome. Thanks all!

Chris
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
Sounds about right to me. Keep your tanks full of cool fuel, travel early
in the day. That's about it. Summer blend fuel only.
Jim Hupy

Hello all:
I was looking for some additional feedback on vapor lock, mainly what kind
of conditions that you have seen it in. We seem to be troubled by it when
temps get up over 83-85 degrees outside, it first started last summer going
down the Florida where temps got up to 93+. Since then, we've had an
inline fuel pump and rebuilt carb installed by JimB, that seems to have
done the trick for getting around the issue (which only seems to happen when
slowing down or stopping and trying to get going again).
Also since the inline fuel pump, we've had an aluminum ported Offenhauser
intake manifold installed, with the Paterson blockoff kit. We had this done
due to cracking of the original manifold. Some thought maybe this would
help with vapor lock, however today we again had it happen to us, temps
outside were around 83-84 degrees with full sun, we were on the highway for
about 45 minutes after taking off cold. After exiting the highway,
stopping at a sign, and accelerating again on a backroad, after 10 seconds
while accelerating the engine starting surging a little bit. After
flipping on the electric aux pump, the surging went away after about 15-20
seconds. We were running the dash AC at the time as well.

Does this seem to be a little bit extreme with it happening when it's 83-84
degrees out, or is this pretty much what everybody else is experiencing?
And is the main fix still just using an aux electric pump back near the
tanks? I can't imagine this could be anything else besides vapor lock.
Over
the years we've had everything in the fuel system either replaced or fixed:
fuel tanks cleaned & coated, new rubber hoses & fuel filter, new solenoid,
new inline fuel pump and fuel system check (by JimB), new Carter mechanical
fuel pump, rebuilt carb (from JimB), new aluminum intake, and even a new
fan clutch (Delco 15-4947). Everything seems to be in order.

Feedback, thoughts and anything else is more than welcome. Thanks all!

Chris
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan

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How hot was the road bed? The low, flat, large surface area of our fuel tanks will absorb road heat easily. Hot gas will cause conditions very similar
to vapor lock. Some have painted the bottom of the gas tanks to reflect road heat.
You might see if you have shielding between the gas tanks and the exhaust pipe. No sense in adding heat to the gas in the tank.
Here in Alabama, Summer afternoons are tough for vapor lock.
Tom, MS II
--
1975 GMC Avion
KA4CSG
 
My experience with the carburated engine was that you'd falter - or quit completely - at the 1 - 2 shift coming off a light with a long cycle. The
engine's been idling, no airflow around the coach, the engine compartment is very hot, and she locks up. At that shift, particularly if your in a
turn MAP climbs to ambient and about the only fuel available is from the acceleration pump. Coast to the roadside, wait ten - fifteen minutes, it
started up and did well as long as I kept moving. This with decent gas, with alcohol laced gtas it will be worse. The cure was a new fan clutch and
a pair of electric pumps in back, taking the mechanical pump out of the system.

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
what coating, mine is steel.

so maybe it did!

________________________________
From: Gmclist on behalf of David H.Jarvis
Sent: Monday, June 5, 2017 11:59:40 AM
To: gmclist
Subject: Re: [GMCnet] Vapor lock feedback

Has anyone had a problem with the ethanol gas dissolving the coating inside the gas tank?

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What you are describing is what I have been fighting ever since I got my coach almost nine years ago. One of the things that helps is to have a fresh
carburetor fuel filter in place. If that filter gets a little bit clogged, it will disrupt the gas flow enough to cause the vapor lock. I have never
had the coach actually stall, but it behaves just as you describe and will do it while climbing a steep grade as well.

I make a habit of turning my electric fuel pump on wherever I anticipate a situation where it might be needed. I usually turn it on when I exit a
freeway and know I will be driving on surface streets or when approaching a long uphill climb.

I have also found that using an ethanol treatment, such as Lucas, seems to help a lot. If you can find non-ethanol gas (pure-gas.org), that makes a
big difference too. Here in the West, there can be thousands of feet of elevation change encountered in a short distance and the 'winter blend' gas
is often sold in areas above 5,000 ft, all year round. Consequently, when you get back down around 2,000 ft or less, the coach doesn't want to run on
it.

As Johnny stated, a good fan clutch makes a difference too, as it helps to circulate cooler air into the engine compartment. I don't think it is
unusual to have vapor lock issues with ambient temperatures as low as 85 degrees, depending on the gas in your tank. I haven't done this (yet) but it
does make sense that eliminating the mechanical fuel pump will eliminate another source of heat for the fuel.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
I was hoping my block off kit would eliminate the vapor lock symptoms. Spring break trip in May was first real run. Full sunny day, mid 80's ambient
temps, and a few stop lights in a row it started to stumble if I sat for any length of time. I put an electric pump in the aux line, but have not
tested it yet.
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
 
> What you are describing is what I have been fighting ever since I got my coach almost nine years ago. One of the things that helps is to have a
> fresh carburetor fuel filter in place. If that filter gets a little bit clogged, it will disrupt the gas flow enough to cause the vapor lock. I
> have never had the coach actually stall, but it behaves just as you describe and will do it while climbing a steep grade as well.
>
> I make a habit of turning my electric fuel pump on wherever I anticipate a situation where it might be needed. I usually turn it on when I exit a
> freeway and know I will be driving on surface streets or when approaching a long uphill climb.
>
> I have also found that using an ethanol treatment, such as Lucas, seems to help a lot. If you can find non-ethanol gas (pure-gas.org), that makes
> a big difference too. Here in the West, there can be thousands of feet of elevation change encountered in a short distance and the 'winter blend'
> gas is often sold in areas above 5,000 ft, all year round. Consequently, when you get back down around 2,000 ft or less, the coach doesn't want to
> run on it.
>
> As Johnny stated, a good fan clutch makes a difference too, as it helps to circulate cooler air into the engine compartment. I don't think it is
> unusual to have vapor lock issues with ambient temperatures as low as 85 degrees, depending on the gas in your tank. I haven't done this (yet) but
> it does make sense that eliminating the mechanical fuel pump will eliminate another source of heat for the fuel.

Yes that is spot on to our behavior... climbing a steep grade definitely does it as I think it's because the engine is working overtime and there
isn't as much air flow. Not many steep grades here in Michigan to test with, though. :)

I was wondering if ethanol treatment does help. Good to know, thanks.

And that's an excellent point on the winter blend, I think we do have some leftover stuff from last fall in the tanks.

Thanks!
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
> I was hoping my block off kit would eliminate the vapor lock symptoms. Spring break trip in May was first real run. Full sunny day, mid 80's
> ambient temps, and a few stop lights in a row it started to stumble if I sat for any length of time. I put an electric pump in the aux line, but
> have not tested it yet.

Sounds very similar. If you have your electric pump on a switch, it does take 15-20 seconds to correct the issue, but in our experience it does the
trick. Once things are running better, I switch the pump back off and we're good until we stop again.
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
Tylor, just the Intake Block off will not help a vapor loc issue. It can
help , but we know through working on these coaches, what it takes to
decrease the problem.
Also how one installs pumps , heat shield and others.

> I was hoping my block off kit would eliminate the vapor lock symptoms.
> Spring break trip in May was first real run. Full sunny day, mid 80's
> ambient
> temps, and a few stop lights in a row it started to stumble if I sat for
> any length of time. I put an electric pump in the aux line, but have not
> tested it yet.
> --
> 1975 Glenbrook, 1978 Royale rear bath
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
I second the little Qjet filter only takes a little shmoots that will cause this same issue. It may not be your issue but they are cheap and I keep a
few in the glove box and replace from time to time. Even though my fuel system has been redone ie. tanks sealed,fuel lines replaced etc . I too have
aux carter and hit it when she starts to stumble seems to help but it has done it to me even with the aux pump on. Has anyone had any luck with the 3
port/return line mechanical pump the Toros had on them to remedy VL ?
--
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
 
Call me and I will tell you where to and how to apply the aux pump.
The mechanical pump with return line can be of help also.

> I second the little Qjet filter only takes a little shmoots that will
> cause this same issue. It may not be your issue but they are cheap and I
> keep a
> few in the glove box and replace from time to time. Even though my fuel
> system has been redone ie. tanks sealed,fuel lines replaced etc . I too have
> aux carter and hit it when she starts to stumble seems to help but it has
> done it to me even with the aux pump on. Has anyone had any luck with the 3
> port/return line mechanical pump the Toros had on them to remedy VL ?
> --
> Tony Cook
> 77' Kingsley ' SuperSession 77 '
> Torrance Beach,CA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
> I second the little Qjet filter only takes a little shmoots that will cause this same issue. It may not be your issue but they are cheap and I
> keep a few in the glove box and replace from time to time. Even though my fuel system has been redone ie. tanks sealed,fuel lines replaced etc . I
> too have aux carter and hit it when she starts to stumble seems to help but it has done it to me even with the aux pump on. Has anyone had any luck
> with the 3 port/return line mechanical pump the Toros had on them to remedy VL ?

We ended up also installing an inline metal filter between the metal line and fuel pump inlet to help keep stuff from getting to the pump, just in
case. Super easy to change out if needed, and is a little larger than the one at the carb. For what it's worth.
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
I as well I think 3 filters total one for the aux/elect pump,one at the front cross member and the Qjet . Probably overkill but you would be amazed at
what the mechanical fuel pump can hide in it. I replaced mine and found so much crud/particles to fine rust in it . That is what was doing my Qjet
filter in often. After new fuel pump changed has been pretty good since.
--
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
 
I have been over this on the net, and done presentations at several rallies
on the West Coast about what many here describe as vapor lock. Don't know
if that is an exact term or not, but, for those of you out there in
GMCVILLE who are having issues with driveability of their coaches on days
warmer than 85 degrees or so, I will try to aproach how to deal with it,
not what causes it.
1. Get rid of your winter fuel.
2. Run with your tanks as full as possible.
3. Drive early in the day when it is cooler.
4. Keep your filters clean, carry spares.
5. Install an inline electric fuel pump after the selector valve.
6. Use ethanol free fuel if possible.
Most of the time, this is all that is needed. The problem is NOT WITH YOUR
COACH. IT IS WITH THE FUEL. So, fixing the coach is NOT going to make your
problems go away totally.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> I second the little Qjet filter only takes a little shmoots that will
cause this same issue. It may not be your issue but they are cheap and I
> keep a few in the glove box and replace from time to time. Even though my
fuel system has been redone ie. tanks sealed,fuel lines replaced etc . I
> too have aux carter and hit it when she starts to stumble seems to help
but it has done it to me even with the aux pump on. Has anyone had any luck
> with the 3 port/return line mechanical pump the Toros had on them to
remedy VL ?

We ended up also installing an inline metal filter between the metal line
and fuel pump inlet to help keep stuff from getting to the pump, just in
case. Super easy to change out if needed, and is a little larger than the
one at the carb. For what it's worth.
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan

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Dump #5, install two electric pumps, and use the tank selector to also select the pump. 50 bux more than one and a simpler setup as well. Cap the
selector valve and toss the mechanical pump in the tool box and you can conver to it in 30 minutes beside the road should the need arise. (It never
did)

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
I live in Arizona and, after almost 11 years of summer fuel problems I think I am finally free of them. In addition to the laundry list of the usual
stuff mentioned here I installed a FiTech EFI with their Fuel Command Center. The Command center (CC) (and the price) was the thing that convinced me.
The CC is a buffer for the bubbles that come from the gas boiling in the tanks and since I installed it I have had no engine vapor issues.

I did continue to have fuel tank issues though - gas boiling in the tanks and venting through the fuel cap, swelling the tanks and making fumes, etc.
So a fellow GMCer (Dan Gibb) and I implemented his idea for insulating the tanks. I have a write up and photos at
http://minniebiz.com/gmcmotorhome/2017/02/25/insulating-the-fuel-tanks/. We did this in February on both of our coaches and even though it wasn't
close to hot until recently I immediately noticed it being easier to fill the tanks - I can't explain that but it has been consistent. On Saturday I
drove from the Tucson area to Lake Havasu with temperatures as high as 115 degrees and filled the tanks twice with no issues at all. Never a stumble
and no fuel fumes or venting - just like a modern car.
--
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
http://www.minniebiz.com
http://www.gmcws.org
 
The science behind it is Where in the system the VL is happening. Probably not between the mechanical pump and carb as this is under pressure ( though
low) but before the mech pump which are poor "suckers". I have the frame mounted pump with relay signaled from the Aux fuel switch signal to the
selector valve. In my case the "fix" is in under 2 seconds ftom the time I flip the switch til the stumble clears. I think the long term road load
heat raises the tank temp over time then in dliw traffic the lines loose airflow and VL occurs. Best to flip to Aux when VL is anticipated.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
> what coating, mine is steel.
>
>
> so maybe it did!
>
> ________________________________
> From: Gmclist on behalf of David H.Jarvis
> Sent: Monday, June 5, 2017 11:59:40 AM
> To: gmclist
> Subject: Re: [GMCnet] Vapor lock feedback
>
> Has anyone had a problem with the ethanol gas dissolving the coating inside the gas tank?
>
> _______________________________________________
> 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

He said he had the fuel tanks cleaned and COATED. That would not be on the outside.
 
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