Home » Public Forums » GMCnet » Assorted fuel issues (Where to start?)
| Assorted fuel issues [message #323320] |
Mon, 04 September 2017 15:14  |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
Karma: 0
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I have a 1978' with a 455 with a Edelbrok performer intake manifold, with what I believe to be the original 403 carburetor installed. Electric choke on the carburetor, but I do not believe the choke has ever Been quite "right" since I Have owned coach. I.e. The choke plate does not completely close when I step up n the accelerator pedal.
I have only the original mechanical fuel pump installed. I did replace that pump ~3 years ago with one from one of the GMC Suppliers.
The coach has always been hard to start after it sits for a couple days. It always took lots of cranking, but would eventually start. I have suspected that my carburetor needs attention as I do not believe it should leak down that fast.
I feel I have a good understanding of how the two tanks are interconnected. Until about 3 months ago, my fuel gauge worked (and seems reasonable accurate-given miles driven and gasoline pumped). But now the gauge reads empty when set to AUX, but seems correct for the main tank. I presume this is due to loose connection in the line to the valve switch.
Also at that time, it became virtually impossible to start the coach, if it has sat for more than 24 hours. I can crank for two or three minutes and no joy.
I have pulled the fuel line out of carb and put in bottle, and I do not see fuel ( which I presume means I need to replace fuel pump again).
I have acquired a boat tank, and hook that to the input of the fuel pump, and it will start on the 2nd or 3rd revolution.
Now I come the part I do not understand....
If I run it from the boat tank briefly (30 seconds - 2 minutes), and then re-connnect the main fuel line, I can drive it that way for miles. I can shut it off, and as long as I start it within an hour or so, it will fire right up from the main tanks. Wait 24 hours, and forget about it though.
Is this is a failure mode of the mechanical fuel pumps?
I have read several of the threads on here about electric fuel pumps, and it seems a lot of people have them, and a lot of people have issues with them too. Also, there seems to be a lot of options about where and how to plumb them and wire them. I must admit, I like the simplicity of the mechanical pump, and I know it used to work better than it does now.
Part of me thinks putting an electric pump in now, would just mask whatever real problems I need to solve.
So what do I attack first?
Thanks.
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
[Updated on: Mon, 04 September 2017 16:53] Report message to a moderator |
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| Re: [GMCnet] Assorted fuel issues [message #323325 is a reply to message #323320] |
Mon, 04 September 2017 16:23  |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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Sounds like a seal problem within the carb allowing the fuel to slink away.
Maybe install a fuel line check valve to lock the fuel in the line. I did a
quick internet search and it looks like less than $20.
Sully
77 eleganza 2
Bellevue.
On Mon, Sep 4, 2017 at 1:15 PM Paul Zerkel wrote:
> I have a 1978' with a 455 with a Edelbrok performer intake manifold, with
> what I believe to be the original 403 carburetor installed. Electric choke
> on the carburetor, but I do not believe the choke has ever Benin quite
> "right" since I Have owned coach. I.e. The choke plate does not completely
> close when I step up n the accelerator pedal.
>
> I have only the original mechanical fuel pump installed. I did replace
> that pump ~3 years ago with one from one of the GMC Suppliers.
>
> The coach has always been hard to start after it sits for a couple days.
> It always took lots of cranking, but would eventually start. I have
> suspected
> that my carburetor needs attention as I do not believe it should leak down
> that fast.
>
> I feel I have a good understanding of how the two tanks are
> interconnected. Until about 3 months ago, my fuel gauge worked (and seems
> reasonable
> accurate-given miles driven and gasoline pumped). But now the gauge reads
> empty when set to AUX, but seems correct for the main tank. I presume this
> is due to loose connection in the line wither to the valve switch.
>
> Also at that time, it became virtually impossible to start the coach, if
> it has sat for more than 24 hours. I can crank for two or three minutes and
> no joy.
>
> I have pulled the fuel line out of carb and put in bottle, and I do not
> see fuel ( which I presume means I need to replace fuel pump again).
>
> I have acquired a boat tank, and hook that to the input of the fuel pump,
> and it will start on the 2nd or 3rd revolution.
>
> Now I come the part I do not understand....
>
> If I run in from the fuel tank briefly (30 seconds - 2 minutes), and then
> re-connnect the main fuel line, I can drive it that way for miles. It can
> shut it off, and as long as I start it within an hour or so, it will fire
> right up from the main tanks. Wait 24 hours, and forget about it though.
>
> Is it his is a failure mode of the mechanical fuel pumps?
>
> I have read several of the threads on here about electric fuel pumps, and
> it seems a lot of people have them, and a lot of people have issues with
> them too. Also, there seems to be a lot of options about where and how to
> plumb them and wire them. I must admit, I like the simplicity of the
> mechanical pump, and I know it used to work better than it did before.
>
> Part of me thinks putting an electric pump in now, would just mask
> whatever real problems I need to solve.
>
> So what do I attack first?
>
> Thanks.
>
> --
> Paul Zerkel
> '78 Eleganza II
> Salisbury IL (near Springfield)
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: Assorted fuel issues [message #323327 is a reply to message #323320] |
Mon, 04 September 2017 16:35 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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It could be that you have a cracked fuel line (hose) somewhere between the tank pickup and the mechanical fuel pump that is sucking air. It can start on the boat tank, then has enough fuel in the carb to run it until it sucks gas through the line, and you don't notice the leak under moderate driving conditions. I'll bet if you drove in excessive heat, and/or up a grade, you would have fuel starvation due to the air getting into the fuel line. When you are cranking the engine on a cold start, the hose has too much air in it to prime the pump and you have a no start condition.
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
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| Re: Assorted fuel issues [message #323328 is a reply to message #323320] |
Mon, 04 September 2017 17:05 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Well if choke is not closing, you have found one of your problems. After sitting a while observe for accelerator pump squirts, if not bowl plugs are probably leaking. You could have a sticking check valve in the pump. When exercised it frees up. If stuck the fuel won't move, just go bad and forth in the line. If you want more headaches install an off shore built electric pump. They have a poor track record.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Assorted fuel issues [message #323329 is a reply to message #323327] |
Mon, 04 September 2017 17:37 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Why don't you call me so we can discuss all your issues as we deal with
them every day and have people from other shops that can assist should I
not be able to address it properly.
We help lot of people an know I can help you.
On Mon, Sep 4, 2017 at 2:35 PM, Carl Stouffer wrote:
> It could be that you have a cracked fuel line (hose) somewhere between the
> tank pickup and the mechanical fuel pump that is sucking air. It can start
> on the boat tank, then has enough fuel in the carb to run it until it
> sucks gas through the line, and you don't notice the leak under moderate
> driving
> conditions. I'll bet if you drove in excessive heat, and/or up a grade,
> you would have fuel starvation due to the air getting into the fuel line.
> When you are cranking the engine on a cold start, the hose has too much
> air in it to prime the pump and you have a no start condition.
> --
> 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
>
> _______________________________________________
> 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@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Assorted fuel issues [message #323338 is a reply to message #323329] |
Mon, 04 September 2017 18:01 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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Another problem, a hot engine will continue to heat the fuel bowl in the carb and the fuel will evaporate. Longer cranking is to fill the bowl.
Did you really mean that you have a 455 with a 403 spec carb? Interesting, at best.
Tom, MS II
1975 GMC Avion for sale
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] Assorted fuel issues [message #323348 is a reply to message #323338] |
Mon, 04 September 2017 20:25 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Paul,
Most of my questions/advice have already been given, but I became concerned
as soon as I saw "Edelbrock Performer manifold". I had one of those when I
got my coach. Before I got it home, the engine destroyed itself. With
that manifold off, I found it cracked where the exhaust crossovers enter
the "chimney" beneath the carburetor. I had it welded, only to have it
crack again quickly. Then I discovered that Edelbrock REQUIRES the use of
iron plugs in the heads' exhaust ports or they won't honor their warranty.
Edelbrock provided those and I installed them. Fortunately, about 22,000
miles later (IIRC), I had to pull the manifold again. Here's what I found,
caused by those REQUIRED plugs;
http://www.gmcmhphotos.com/photos/g3057-cylinder-head-damage-from-exhaust-crossover-plugs.html
Only a few more miles would probably have cost me an entire engine. I know
of at least one friend who had that exact experience: The plugs wore into
the water jacket, flooded the cylinders, bent lots of stuff, including the
rods with the hydraulic lock.
SO, if you do not have those plugs, your problem is probably caused by the
excessively heated manifold causing all the fuel to evaporate from the fuel
bowl, and possibly contributing to partial vapor lock. If you DO have the
plugs, then you're in even greater danger: They're likely to destroy your
cylinder heads, and possibly the whole engine. I think you need to pull
the manifold and find out.
My original solution was to pour "Mondello Metal" into the exhaust
crossover (this was before SS blockoff plates became popular). The final,
and best, solution was to get rid of the Edelbrock and install an OEM
manifold (the Rockwell aluminum manifold -- WITHOUT CROSSOVER -- was not
then available). Did it cost me any power to remove the Edelbrock? Not
below 4000 rpm. :-)
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc., etc.
www.gmcwipersetc.com
On Mon, Sep 4, 2017 at 7:01 PM, Thomas Phipps wrote:
> Another problem, a hot engine will continue to heat the fuel bowl in the
> carb and the fuel will evaporate. Longer cranking is to fill the bowl.
> Did you really mean that you have a 455 with a 403 spec carb? Interesting,
> at best.
> Tom, MS II
> 1975 GMC Avion for sale
> --
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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