Home » Public Forums » GMCnet » HELP! Runs perfect then just dies! (RESOLVED!)
| HELP! Runs perfect then just dies! (RESOLVED!) [message #352642] |
Sun, 08 March 2020 14:42  |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Hello all! Seeking some help once again..
I've just done a full rehab of my fuel system and to my surprise, it fired right up and ran beautifully. Sadly, it died after about a minute and would not start again. When It died it was like i turned the ignition off. No stutter or strange behavior. Wait 15 minutes and it flashes right up and again, runs beautifully then dies in the same manner as before. I'm sure i could repeat this process but only tried it twice before posting here.
Should be noted that it ran fine previous to the rehab but I'm doing a full restore so the floors are out. Figured it was a no-brainer to do this stuff now.
What I have done/replaced and not done in the rehab;
Dropped tanks and repainted.
New sending units.
All new rubber fuel lines. Like every single one.
Added a twist off fuel filter, and fuel pump to the aux tank to prevent vapour lock issues
New selector switch.
Installed the insulated carb to pump fuel line from Jim K.
Did not replace the vapor separator and did find that it was not sealed so I sealed up a crack with some rtv.
Did not replace the vapor canister or do anything with it at all.
I just want to reiterate that it did run fine before so my thought is it is not likely to be either of the two things i didn't replace.
Thanks for reading and any help is appreciated as always!!
Shawn
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
[Updated on: Tue, 10 March 2020 17:21] Report message to a moderator |
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| Re: HELP! Runs perfect then just dies [message #352643 is a reply to message #352642] |
Sun, 08 March 2020 15:28  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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well it's either giving out of gas - or getting waay too much - or giving out of sparks. Investigate further and report back.
--johnny
Foolish Carriage, 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
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| Re: HELP! Runs perfect then just dies [message #352645 is a reply to message #352643] |
Sun, 08 March 2020 15:57 |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Johnny Bridges wrote on Sun, 08 March 2020 15:28well it's either giving out of gas - or getting waay too much - or giving out of sparks. Investigate further and report back.
--johnny
Yes, I understand the principles of a gasoline engine. I'm seeking advice on how/where to investigate and to see if this sounds like an issue that is familiar with someone.
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
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| Re: HELP! Runs perfect then just dies [message #352647 is a reply to message #352642] |
Sun, 08 March 2020 17:07 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Shawn,
I am very much in agreement with our Canadian friend from Mexico.....
This has happened (never to me because I won't have HEI) to three engines I have had experience with, and I would like you to think that I immediately came to a solid diagnosis. The definition of immediate here has to be a little loose.
You replaced all the rubber lines including those on top of the tank? If you have not, you should.
If it has to crank a while to restart, suspect the fuel.
If you check the accelerator pump and it does not squirt fuel, suspect the fuel.
As Bruce wrote, if it does not sputter just quits, suspect the spark.
If you check the accelerator pump and it squirts fuel, suspect the spark.
If you can wait a while and it fires right up again, suspect the spark.
Next time you are messing with it have a long phillips screw driver handy.
When she quits, pull a plug wire and put in on the screw driver. Arrange the screwdriver to be close to something on the engine and crank.
**Caution** If you crank with a plug wire disconnected, that will often take out the module with a single event.
¿¿Did You see a big spark??
Tell us when you know more.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: HELP! Runs perfect then just dies [message #352650 is a reply to message #352642] |
Sun, 08 March 2020 19:16 |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Senior Member |
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Thanks fellas.
I ordered a new hei module. We'll see if that does the trick. I'll do the plugs and wires while I'm at it.
And yes Matt, all fuels replaced. On top of tanks as well.
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
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| Re: HELP! Runs perfect then just dies [message #352656 is a reply to message #352642] |
Mon, 09 March 2020 07:50 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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I agree HEI is more likely than what I'm about to suggest.
Are you sure you got the fuel pick up hoses on correct connection at tank? If you reverse them, you are trying to draw gas from the vent pipe, which does not run fully into the tank. If you have an auxillary electric fuel pump this is easier to test (pull end and let her rip into spare tank for a few minutes).
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: HELP! Runs perfect then just dies [message #352702 is a reply to message #352642] |
Tue, 10 March 2020 15:50 |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Well... a bit of a silly resolution to this issue. My motorhome is parked on quite an angle in my driveway, nose down. I put 20 gallons of fuel in the tanks but it was not enough to fill the rear tank. As suggested by Tilerpep, i pulled off the rear sending unit to ensure proper orientation of the hoses and discovered the tank was near empty. Put another 20 gallons in it and she flashed right up and kept on going. Problem solved with a silly oversight on my behalf.
Silver linings;
Ill now have a spare HEI module for when it does go bad (now that i know this is a common failure point)
Ordered new plugs (NGK 7355)and wires (Dick Patersons) that I was considering holding off on.
I now know that 20 gallons of fuel will stay in the front tank and leave nothing in the back. Scary thought going down hills!
Most importantly, I know everything I did works as it should. So far...
Thanks for the help fellas!
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
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| Re: HELP! Runs perfect then just dies! (RESOLVED!) [message #352704 is a reply to message #352642] |
Tue, 10 March 2020 18:47 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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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://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://gmcmotorhome.info/addens.html#pump
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
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| Re: HELP! Runs perfect then just dies! (RESOLVED!) [message #352705 is a reply to message #352642] |
Tue, 10 March 2020 19:13 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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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
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| Re: HELP! Runs perfect then just dies! (RESOLVED!) [message #352707 is a reply to message #352704] |
Tue, 10 March 2020 20:25 |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Senior Member |
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RF_Burns wrote on Tue, 10 March 2020 18:47My 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://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://gmcmotorhome.info/addens.html#pump
Interesting reads Bruce! I basically had what was happening in picture #4 there...
That booster pump sounds like a heck of a good idea. Consider it added to the never-ending list.
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
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| Re: HELP! Runs perfect then just dies! (RESOLVED!) [message #352708 is a reply to message #352705] |
Tue, 10 March 2020 20:31 |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Senior Member |
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Tilerpep wrote on Tue, 10 March 2020 19:13The 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!
What was interesting was I actually did try the aux pump and it didn't seem to help when i first had the issue. This time when it was trying to draw fuel all the way from the rear tank with empty lines, i gave it a shot with that aux pump and it fired right up. Helped out that mechanical that was struggling with empty lines. Point is I know it works but i was bit gun-shy originally to let it run too long. Wasn't sure if it would be sending too much fuel so i didn't leave it on for very long. Maybe had i left it on it would have started/run fine. I only put in there for the known vapour lock issues...
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
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| Re: HELP! Runs perfect then just dies! (RESOLVED!) [message #352727 is a reply to message #352708] |
Thu, 12 March 2020 10:05 |
Joe Weir
Messages: 769
Registered: February 2013
Location: Columbia, SC
Karma: 7
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Senior Member |
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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.
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| Re: [GMCnet] HELP! Runs perfect then just dies! (RESOLVED!) [message #352729 is a reply to message #352727] |
Thu, 12 March 2020 10:21 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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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:
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>
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| Re: [GMCnet] HELP! Runs perfect then just dies! (RESOLVED!) [message #352731 is a reply to message #352705] |
Thu, 12 March 2020 10:54 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Mar 10, 2020, at 8:13 PM, Tyler via Gmclist wrote:
> 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
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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. Ill double check but I'm pretty sure I have them in the right place. Thanks for the suggestion.