Home » Public Forums » GMCnet » [GMCnet] LarC's power loss/stalling problem
| [GMCnet] LarC's power loss/stalling problem [message #55263] |
Wed, 02 September 2009 13:23  |
Richard Brown
Messages: 281
Registered: May 2009
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This sounds like a situation I once had with an old Buick years ago. You might try what I did. Remove the gas cap, disconnect the fuel supply line at the fuel pump, and use compressed air to backflush the line. My problem turned out to be partial clogging of the filter sock in the tank.The sock will soon stop back up, but you'll know what it is. I also attached a strong magnet to the outside of the tank between the filler and the sender/fuel outlet. It costs nothing to try this & it may help out on the road.
Richard & Carol Brown
PO Box 941
Lindale, TX. 75771
1974 GMC Eleganza SE
wings77sporty@sbcglobal.net
(903)881-0192
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Richard & Carol Brown
1974 Eleganza SE
1174 Hickory Hills Dr.
Murchison, TX. 75778
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| Re: [GMCnet] LarC's power loss/stalling problem [message #55264 is a reply to message #55263] |
Wed, 02 September 2009 13:35  |
Tin Gerbil
Messages: 236
Registered: October 2006
Location: Vancouver Island, B.C.
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Richard;
You normally blow a large hole in the sock, if you use enough air
pressure the first time.
Are you sure using the magnet to line up the fuel molecules, did not
solve the problem and increase your mileage?
Gordon
Richard Brown wrote:
> This sounds like a situation I once had with an old Buick years ago.
> You might try what I did. Remove the gas cap, disconnect the fuel
> supply line at the fuel pump, and use compressed air to backflush the
> line. My problem turned out to be partial clogging of the filter sock
> in the tank.The sock will soon stop back up, but you'll know what it
> is. I also attached a strong magnet to the outside of the tank
> between the filler and the sender/fuel outlet. It costs nothing to
> try this & it may help out on the road.
>
> Richard & Carol Brown PO Box 941 Lindale, TX. 75771 1974 GMC Eleganza
> SE wings77sporty@sbcglobal.net (903)881-0192
> _______________________________________________ GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Gordon
'74 Canyon Lands "Tin Gerbil"
Vancouver Island, B.C.
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| Re: [GMCnet] LarC's power loss/stalling problem [message #55371 is a reply to message #55263] |
Thu, 03 September 2009 03:52 |
Richard Brown
Messages: 281
Registered: May 2009
Karma: 1
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First off, I didn't suggest hitting it with a few hundred pounds of pressure. I used a bicycle pump. Second, you'll find that the fuel sock is more robust than you think. When I pulled out the sender later, the sock wasn't blown out or deformed in any way. It was made of brass screen. Third, the magnet has nothing whatsoever to do with fuel molecules. It has to do with rust, which last I checked was collected by magnets. Not as well as filings, but it will collect them to an extent. I used air as a roadside fix, anyway.
BTW, if you folks are trying to get a rise out of me, you're wasting your time. I take what's said here with a large grain of salt as it is. I never take anyone's word as the final authority without verifying the info first. I may "only" be 50, but I've learned not to take anything at face value. There are too many other sources of information available to put faith in just one or 2.
I don't feel disappointed by the way folks act anymore; I don't expect that much from folks, anyway.
Richard & Carol Brown
PO Box 941
Lindale, TX. 75771
1974 GMC Eleganza SE
wings77sporty@sbcglobal.net
(903)881-0192
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Richard & Carol Brown
1974 Eleganza SE
1174 Hickory Hills Dr.
Murchison, TX. 75778
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| Re: [GMCnet] LarC's power loss/stalling problem [message #63354 is a reply to message #55263] |
Sat, 07 November 2009 09:16 |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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To your excellent list of possible problems, my genius mechanic friend adds:
Add to that "sticking centrifugal advance in distributor" causing no timing advance at higher RPM. Common on HEI
> >
>> > > This saga has gone on too long and I know I've forgotten many of
> > the
>> > > details. I know that "too long" for me means "enduring nightmare"
> > for
>> > > you, but I thought I would think out loud to all the possibilities
>> > > once again and let you check them off.
>> > >
>> > > The symptom is that the engine runs fine at times, but then for no
>> > > apparent reason loses power to a debilitating level.
>> > >
>> > > Just working back from first principles, and engine produces power
> > by
>> > > compressing a fuel/air mixture and then igniting it. The expansion
>> > > caused by the ignition creates power. Power is therefore related to
>> > > how much of the fuel/air mixture the engine can compress.
>> > >
>> > > That said, here are what seem to me the possible causes:
>> > >
>> > > 1. No fuel. This would prevent the ignition from producting power.
>> > >
>> > > 2. A restriction on air intake, which would reduce the amount of
>> > > fuel/air mixture and therefore the power.
>> > >
>> > > 3. A restriction on exhaust, which would cause exhaust to back up
> > into
>> > > the cylinders, reducing the ability of the engine to pump in fresh
>> > > fuel/air mixture.
>> > >
>> > > 4. A loss of ignition.
>> > >
>> > > 5. A loss of compression.
>> > >
>> > > In the "no fuel" category, here are the possible faults:
>> > >
>> > > 1a. Blocked-up fuel tank inlets. You have eliminated this
> > possibility
>> > > by using an alternate fuel source upstream from the pump.
>> > >
>> > > 1b. Faulty selector valve. Also eliminated.
>> > >
>> > > 1c. Faulty pump.
>> > >
>> > > 1d. Blocked filter.
>> > >
>> > > 1e. Collapsed or leaking fuel hose (a leak upstream from the pump
> > can
>> > > draw air and kill the pumping action).
>> > >
>> > > 1f. Blocked carburetor float valve.
>> > >
>> > > 1g. Faulty carburetor.
>> > >
>> > > In the "air restriction" category, here are the possible faults:
>> > >
>> > > 2a. Heat stove flapper valve.
>> > >
>> > > 2b. Faulty valve train preventing intake valves from opening
> > reliably.
>> > >
>> > > 2c. Leaking manifold pulling air in without fuel.
>> > >
>> > > 2d. Plugged air filter (I'm sure this has been eliminated).
>> > >
>> > > 2e. Faulty carburetor, particularly in the ability of the carb to
> > open
>> > > the throttles and close the choke. I can't see how this could be
>> > > intermittent, though, except for the secondaries, which should not
>> > > have an effect on normal driveability in any case.
>> > >
>> > > In the exhaust restriction category, we have:
>> > >
>> > > 3a. Neighbor put a potato in the tail pipe.
>> > >
>> > > 3b. Mouse house in the exhaust. (I'm particularly prepared to
> > believe
>> > > this is possible.)
>> > >
>> > > 3c. Broken baffle in a muffler causing intermittent blockage (do
> > not
>> > > underestimate this possibility).
>> > >
>> > > 3d. Exhaust valves that do not open reliably. I would think this
> > would
>> > > cause secondary damage that would be hard to miss. (Closing is
> > another
>> > > matter, but that's down the list.)
>> > >
>> > > For ignition, we have:
>> > >
>> > > 4a. Ignition coil. These can have heat-sensitive failures easily.
>> > >
>> > > 4b. Distributor faults (including moisture forming inside it if you
>> > > live in exceptionally humid conditions). Pickup coil, etc.
>> > >
>> > > 4c. Plug wires.
>> > >
>> > > 4d. Plugs (can't see how this would be an issue unless they are
> > being
>> > > fouled intermittently).
>> > >
>> > > 4e. Supply voltage and grounding (which can be sneaky).
>> > >
>> > > And, finally, for compression, there is:
>> > >
>> > > 5a. Intake valves not closing, though this would cause backfires
>> > > through the intake when the problem is presenting itself.
>> > >
>> > > 5b. Exhaust valves not closing, which might also cause backfires,
> > but
>> > > out the exhaust.
>> > >
>> > > 5c. Loss of compression around pistons, but I don't see how this
> > can
>> > > be intermittent, unless maybe there is a crack. Even so, the engine
>> > > will make fully usable power on seven cylinders (ask me how I
> > know).
>> > >
>> > > A fuel flow test is one way to test many parts of Category 1. A
>> > > leakdown test will check many parts of several of the categories,
> > but
>> > > only in the static condition and the problem seems to require a
>> > > combination of dynamic conditions to present itself. Sticky valves
>> > > would have other symptoms than just power loss, including
> > interesting
>> > > burbles and backfires. Plug wires can be faulty and still look
> > good,
>> > > and tend to present their fault and times when the ignition system
> > is
>> > > being asked to produce the most voltage to create the spark. I had
> > a
>> > > Subaru present that problem to me, and it only occurred when I
> > tried
>> > > to put my foot in the throttle. The one thing I don't recall that
> > you
>> > > checked is the exhaust system.
>> > >
>> > > I'm sure you can check off most of the items on the list, but
>> > > sometimes it helps to try to go back and reconsider all the
>> > > possibilities to ensure you are not hiding from yourself.
>> > >
>> > > Rick "pondering a slip-on screen over the tailpipe for winter
> > storage"
>> > > Denney
>> > >
>> > > '73 230 Ex-Glacier "Jaws"
>> > > Northern Virginia
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] LarC's power loss/stalling problem [message #63687 is a reply to message #63650] |
Tue, 10 November 2009 10:52 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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Senior Member |
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I had a similar problem.....I had a completely new HEI system from one of our excellent vendors...Engine would hesitate and not run below 1500rpms. Carb was rebuilt to one of our GMC suppliers specs......switched to s different carb....same result....I had an old spare electronic module....I put it in and the engine ran fine...I spent all summer trying to get this thing running right.....cost me a lot of money...hired 2 different mechanics to come to my farm......worth a try.....Brian 77ele 455
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Well Essentially, I have done this. This problem has occurred with the existing points system, then was changed to the "working" HEI system. WHen we found the ground strap was missing from the coil case to ground and had burnt the low voltage wiring up, we renewed the coil, sensor and module.
So I have done this twice now to no changes on performance.
I will note this however since nothing is making any difference.
Thank you
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: [GMCnet] LarC's power loss/stalling problem [message #63725 is a reply to message #63713] |
Tue, 10 November 2009 16:49 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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Larry, the thread has gotten so long I can't recall if you checked your intake for cracks.
_____________________________________________________
We had checked externally for cracks.
We found a plate leaking air, the plate covered the holes for some kind of epa device. Once we sealed that, the engine ran sweet, purrred like a kitten.
I have not checked further though I am getting comments about checking further....
any comment?
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: [GMCnet] LarC's power loss/stalling problem [message #63726 is a reply to message #63725] |
Tue, 10 November 2009 16:52 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""I have not checked further though I am getting comments about checking further....
any comment?""
It's pretty easy to check while the carb is off. Your symptoms could be caused by a crack depending on how serious it is. It's a very common occurence. I have a 403 which started displaying symptoms of very lean running and think I have a crack but need to clean up the area to see for sure. It's worth a look and easy to do while the carb is off.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] LarC's power loss/stalling problem [message #63728 is a reply to message #63726] |
Tue, 10 November 2009 16:57 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Larry--I wanted to mention that in my case I thought I had found the problem right away when I noticed the carb was loose. However, I think I have at least a couple of contributers and that's what makes some of these issues so hard to find. At a minimum, when you see and fix something that could contribute, in the end you have made good headway. When you find the final culprit, it's going to run like never before!! Hang in there.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] LarC's power loss/stalling problem [message #63823 is a reply to message #63760] |
Wed, 11 November 2009 09:42 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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how much vacuum do you have at idle and at 1500rpm...brian77 ele455
________________________________________________________
Always held at least 18 to 20 vacuum.
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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| Re: [GMCnet] LarC's power loss/stalling problem [message #65521 is a reply to message #55263] |
Tue, 24 November 2009 11:50 |
Gary Mau
Messages: 152
Registered: February 2004
Location: Davenport, Iowa
Karma: 0
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Larry,
I noticed in another string that you mentioned being happy to go over 30 mph again. Guess I missed the solution to your stalling problem. Could you tell us again what you finally found. Inquiring minds want to know!
Thanks,
Gary Mau
Former 76 Royale owner
Davenport, IA
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| Re: [GMCnet] LarC's power loss/stalling problem [message #65750 is a reply to message #65521] |
Thu, 26 November 2009 13:30 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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One of the bad things about this forum, is the threads tend to split. This string is a spin-off from the main thread.
http://gmc.mybirdfeeder.net/GMCforum/index.php?t=tree&goto=64801&rid=455#msg_64801
The sad truth is, I don't know what the cause is yet.
I told the mechanic that I wanted hard evidence to the cause but we ended up replacing everything from the fuel pump forward.
I can't tell you about the carborator controversy because the Pirate Carb rebuilder the part supplier uses, seems to have either lost my carb or made up stuff that would not have fit what was happening to my GMC. I have several carb specialists that verified this.
Using the aux fuel tank and still having the problem eliminated the fuel system up to the fuel pump. ( at least for the moment )
One of the things that I hoped would be the answer was the Distributor coil that was missing the ground to the coil frame. We found the lo voltage wiring burnt up from the hi voltage arcing from the coil frame to the low voltage wiring for ground.
Fuel pump was replaced because the existing pump seemed to have a leak from inside.
I did get a rebuilt carb back, but by the number indicated, it is not a GMC Motorhome Carb. I can complain, but I need a carb, a working carb, this one seems to be working.
We did another fuel flow test and cut the inline filter in half before installing the rebuilt " Pirate Carb " and thankfully, she ran.
AS for the cause, and why it showed up originally when the fuel tanks were dropped and the hoses were replaced, I have no clue!
There was nothing to use as a base line as we kept finding a problem with different components, which changed the baseline again.
What keeps me wondering is the fact that the problem keeps coming back... we never find any debri in the filters.
If it comes back again, I have a couple of thoughts but this is or has been one of the most frustrating problems to try to correct. THERE IS NO DOUBT WHY SOME OF THE GMC's ARE ABANDONED IF THEY ARE HAVE THESE KIND OF PROBLEMS. You just plain get worn down and tired of spending the money to try to find it.
Thanks for your input.
To all our dog lovers
insert commands, sit, beg, rollover etc, kiss
http://www.idodogtricks.com/index_flash.html
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
[Updated on: Thu, 26 November 2009 19:40] Report message to a moderator |
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