| VAPOR LOCK or What?? [message #282344] |
Fri, 17 July 2015 15:38  |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Senior Member |
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I think I have read every forum post about vapor lock over the past 13 years that I have been driving this coach. But I had never had the first hand joy till last week. Not sure that is my problem.
On a trip from Red Bluff to Lake Almanor; about 70 miles rising from 300" elevation to 5600" and back down to 4500', temp about 95 in the valley down to less than 80 at the lake the engine seemed to be intermittently starving for fuel on the hills. Ran fine on the flats and minor grades. While at almanor I replaced the inline fuel filter. The old on was clear and has only been in use since the engine rebuild.
This is a regular route in the gmc. Have driven it dozens of times over the years in much hotter temps- towed my Jeep Cherokee many times. Never a problem in the past. Did not tow the Jeep on either of the recent trips.
The week before the trip I had dropped the rear tank to replace all the fuel, vent, vapor separator, and onan fuel lines. So I thought maybe I had pinched the fuel line. Dropped the tank again yesterday to make sure lines are free. Found nothing wrong. Pulled the carb to check the filter-There is none installed.
Drove up to Almanor yesterday afternoon and the starvation symptom(if that is what it is) was worse).Started the trip at +/-100deg. Slowed to 25-30 mph in 2nd gear on the multi-mile 6% grades.
Symptom is a momentary hesitation/slowing/surging only the grades. Runs fine otherwise.
455 has about 15000 miles on it since rebuilt. Headers, single muffler, 3 in exhaust 3:70 final drive, 180 deg thermostat, new mechanical fuel pump when engine rebuilt, elec fuel pump was turned ON . Filled up with fresh fuel (Arco 87) immediately before each trip. Engine temperature never rose above +/- 195.
I replaced the carb a few months ago. Not sure but I think this is the first time up this route since changing the carb. However I have been over The Grapevine(much longer 6% grade) on I-5 while towing the jeep with no problem since changing the carb.
Could this be electrical issue rather than vapor lock? I have spare ignition parts and can change.
Any one have any suggestions?
Thanks
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: [GMCnet] VAPOR LOCK or What?? [message #282346 is a reply to message #282344] |
Fri, 17 July 2015 16:01  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Gene, do you regularly frequent that same ARCO station? Could it be a low
volume station with left over winter gasoline? Doubt that the fuel lines
are a problem, unless, you might have a loose hose clamp that would allow
air into the fuel supply lines. It might also be the centrifugal advance
weights in the distributor hanging up, a 4 pin module, or ignition coil.
Have you changed spark plugs recently and if you did, what is the gap?
Should be .040 - .045". Does your electric pump have a check valve bypass?
Jim Hupy
On Jul 17, 2015 1:39 PM, "gene barrow" wrote:
> I think I have read every forum post about vapor lock over the past 13
> years that I have been driving this coach. But I had never had the first
> hand
> joy till last week. Not sure that is my problem.
>
> On a trip from Red Bluff to Lake Almanor; about 70 miles rising from 300"
> elevation to 5600" and back down to 4500', temp about 95 in the valley down
> to less than 80 at the lake the engine seemed to be intermittently
> starving for fuel on the hills. Ran fine on the flats and minor grades.
> While at
> almanor I replaced the inline fuel filter. The old on was clear and has
> only been in use since the engine rebuild.
>
> This is a regular route in the gmc. Have driven it dozens of times over
> the years in much hotter temps- towed my Jeep Cherokee many times. Never a
> problem in the past. Did not tow the Jeep on either of the recent trips.
>
> The week before the trip I had dropped the rear tank to replace all the
> fuel, vent, vapor separator, and onan fuel lines. So I thought maybe I had
> pinched the fuel line. Dropped the tank again yesterday to make sure lines
> are free. Found nothing wrong. Pulled the carb to check the filter-There is
> none installed.
>
> Drove up to Almanor yesterday afternoon and the starvation symptom(if that
> is what it is) was worse).Started the trip at +/-100deg. Slowed to 25-30
> mph in 2nd gear on the multi-mile 6% grades.
> Symptom is a momentary hesitation/slowing/surging only the grades. Runs
> fine otherwise.
>
> 455 has about 15000 miles on it since rebuilt. Headers, single muffler, 3
> in exhaust 3:70 final drive, 180 deg thermostat, new mechanical fuel pump
> when engine rebuilt, elec fuel pump was turned ON . Filled up with fresh
> fuel (Arco 87) immediately before each trip. Engine temperature never rose
> above +/- 195.
>
> I replaced the carb a few months ago. Not sure but I think this is the
> first time up this route since changing the carb. However I have been over
> The
> Grapevine(much longer 6% grade) on I-5 while towing the jeep with no
> problem since changing the carb.
>
> Could this be electrical issue rather than vapor lock? I have spare
> ignition parts and can change.
>
> Any one have any suggestions?
>
> Thanks
> --
> Gene Barrow
> Lake Almanor, Ca.
> 1976 Palm Beach
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: VAPOR LOCK or What?? [message #282347 is a reply to message #282344] |
Fri, 17 July 2015 16:14 |
armandminnie
Messages: 864
Registered: May 2009
Location: Marana, AZ
Karma: 2
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Senior Member |
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I think it could be an ignition problem - it is very difficult to tell the difference. I do want to tell you about not having a filter in the carburetor though. A few years ago I removed the filter from my carb and everything went great until I swapped the inline filter I have installed ahead of my electric fuel pump. I had a day of fighting with your same symptoms - swapping everything but fixing nothing. I finally figured out that some fibers that looked a lot like the filter element in the Wix inline filter were clogging up the works in the carb - I had to take it apart to clean it. I still didn't replace the carb filter for a couple of more years until I got some gas with dirt in it. Some of that dirt (it was black and very obvious in the filter) got through the inline filter and into the carb but apparently washed out without disassembling the carb like the first time. I have now installed a filter in the carb and figure if that inline filter works it should never (right!) get dirty.
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
visit my gmc blog
click here to visit gmcws.org
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| Re: [GMCnet] VAPOR LOCK or What?? [message #282366 is a reply to message #282344] |
Fri, 17 July 2015 22:43 |
Arthur Mansfield
Messages: 290
Registered: April 2010
Karma: 0
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Senior Member |
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test
On Jul 17, 2015, at 3:38 PM, gene barrow wrote:
> I think I have read every forum post about vapor lock over the past 13 years that I have been driving this coach. But I had never had the first hand
> joy till last week. Not sure that is my problem.
>
> On a trip from Red Bluff to Lake Almanor; about 70 miles rising from 300" elevation to 5600" and back down to 4500', temp about 95 in the valley down
> to less than 80 at the lake the engine seemed to be intermittently starving for fuel on the hills. Ran fine on the flats and minor grades. While at
> almanor I replaced the inline fuel filter. The old on was clear and has only been in use since the engine rebuild.
>
> This is a regular route in the gmc. Have driven it dozens of times over the years in much hotter temps- towed my Jeep Cherokee many times. Never a
> problem in the past. Did not tow the Jeep on either of the recent trips.
>
> The week before the trip I had dropped the rear tank to replace all the fuel, vent, vapor separator, and onan fuel lines. So I thought maybe I had
> pinched the fuel line. Dropped the tank again yesterday to make sure lines are free. Found nothing wrong. Pulled the carb to check the filter-There is
> none installed.
>
> Drove up to Almanor yesterday afternoon and the starvation symptom(if that is what it is) was worse).Started the trip at +/-100deg. Slowed to 25-30
> mph in 2nd gear on the multi-mile 6% grades.
> Symptom is a momentary hesitation/slowing/surging only the grades. Runs fine otherwise.
>
> 455 has about 15000 miles on it since rebuilt. Headers, single muffler, 3 in exhaust 3:70 final drive, 180 deg thermostat, new mechanical fuel pump
> when engine rebuilt, elec fuel pump was turned ON . Filled up with fresh fuel (Arco 87) immediately before each trip. Engine temperature never rose
> above +/- 195.
>
> I replaced the carb a few months ago. Not sure but I think this is the first time up this route since changing the carb. However I have been over The
> Grapevine(much longer 6% grade) on I-5 while towing the jeep with no problem since changing the carb.
>
> Could this be electrical issue rather than vapor lock? I have spare ignition parts and can change.
>
> Any one have any suggestions?
>
> Thanks
> --
> Gene Barrow
> Lake Almanor, Ca.
> 1976 Palm Beach
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: VAPOR LOCK or What?? [message #282369 is a reply to message #282344] |
Fri, 17 July 2015 23:53 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Happens on the hills mostly. Classic symptom of vapor lock ,winter gasoline or plugged filter. Is it a lot worse if you don't turn on the electric pump? If it is the fuel or vapor lock it would help if you top off the fuel tanks with fresh fuel before you start climbing toward almanor. Had that happen to me between red bluff and susanville .I stopped to fill the tanks and had to wait a 1/2 hour before I could remove the gas cap as the gas in the tank was boiling and blowing out in my face. Also is the fuel change over valve in good shape?
Roy Keen
Minden,NV
76 X Glenbrook
[Updated on: Fri, 17 July 2015 23:55] Report message to a moderator |
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| Re: [GMCnet] VAPOR LOCK or What?? [message #282383 is a reply to message #282346] |
Sat, 18 July 2015 09:44 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Senior Member |
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Thanks Jim, Roy, and Armand,
The Arco is a high volume station located next to the Home Depot and Holiday in Express. I only mentioned that it was Arco because some people say their gas is low quality. I drive the GMC a lot so there is never old gas in my tanks. I had just emptied the tanks so I could drop the rear to replace lines. I re-filled immediately before the each trip up the hills.
I checked the plugs yesterday. All were burning clean- light tan to whitish color. Maybe too lean? Gaps were beyond .055- re-gapped to .045 as Jim suggested.
No.1 plug wire had been living too close to the header- had a hot spot with small crack and appeared to be leaking electricity. Taped it up and relocated it away from header.
Took test drive over Fredonyer Summit (5751 ele. East bound trip had no issue. Coming back up the other side I had the starvation symptoms again. Not as extreme as before but still very noticeable.
Turning on the electric pump does not improve performance. The pump was on the coach when I bought it. It has always worked in the past. I verified its operation last February.
Don't know brand or if it has bypass relief or not.
Assuming the pump is functioning I am thinking the symptoms are ignition related.
After dark I ran the engine with the hatch off to see if I had a light show- Nothing.
Will check distributer weights today and replace the module. If symptoms persist I'll change the coil. Trying one thing at a time to isolate the source.
If I can get a new set of plugs and wires I will change them. Although all the ignition components except the pick-up coil were replaced 15,000 miles ago- Jan 2014.
All other suggestions are welcomed.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: [GMCnet] VAPOR LOCK or What?? [message #282433 is a reply to message #282383] |
Sun, 19 July 2015 00:42 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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When ever I had vapor lock problems turning on the electric pump that was in the aux tank line near the tank helped a bunch. If it doesn't help on yours I would check the pump to be sure it is actually pumping . I have since removed my machanical pump and changeover valve and located 2 carter electric pumps and filters outside the frame rails. So far no vapor lock. I would think if it were a coil or module it would cause a problem anytime not just climbing. A filter restriction would mostly act up climbing or anytime you have your foot in the throttle.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: VAPOR LOCK or What?? [message #282434 is a reply to message #282347] |
Sun, 19 July 2015 00:48 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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armandminnie wrote on Fri, 17 July 2015 14:14I think it could be an ignition problem - it is very difficult to tell the difference. I do want to tell you about not having a filter in the carburetor though. A few years ago I removed the filter from my carb and everything went great until I swapped the inline filter I have installed ahead of my electric fuel pump. I had a day of fighting with your same symptoms - swapping everything but fixing nothing. I finally figured out that some fibers that looked a lot like the filter element in the Wix inline filter were clogging up the works in the carb - I had to take it apart to clean it. I still didn't replace the carb filter for a couple of more years until I got some gas with dirt in it. Some of that dirt (it was black and very obvious in the filter) got through the inline filter and into the carb but apparently washed out without disassembling the carb like the first time. I have now installed a filter in the carb and figure if that inline filter works it should never (right!) get dirty.
Good advise Armand I have good sized filters at my electric pumps but keep the filter in the carb to be sure no crap can get in my needle seat.
Roy Keen
Minden,NV
76 X Glenbrook
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