| Need some advice [message #69476] |
Sun, 03 January 2010 14:28  |
docsdad
Messages: 32
Registered: May 2008
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Got in our 75 Avion before Christmas to go to my sons house in IL. On starting out found when going up slight grades, the cruise control was having to pull throttle wide open to make it up minor hills. In two occasions, had back firing occur, or firing through the exhaust. Turned around and came back to town. While driving in town, could hear major pinging when I took off from stop lights. Preignition. I left MH here and took my sons Tahoe for the trip. I am back home and have pulled top off HEI, the advance moves fine both mechanical and vacumn, When starting and idling while warming up, I get black smoke and black suet on the ground out of the exhaust. Warms up, choke comes off and it starts and idles ok, but appears rich until choke comes off. Idles a little rough with the choke on, but no major problem. Need some suggestions for directions to go. It is 455 engine, carb, HEI ignition. Have not had problem last fall when I drove and have driven into Augusta several times last fall with no problems. Unit has been sitting in back yard, I start on weekly basis and warm up. Filled with gas just few days before starting on on the trip. Your suggestions please.
Jim Thompson Thomson GA. 75 Avion
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| Re: Need some advice [message #69497 is a reply to message #69476] |
Sun, 03 January 2010 17:04  |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| docsdad wrote on Sun, 03 January 2010 12:28 |
Got in our 75 Avion before Christmas to go to my sons house in IL. On starting out found when going up slight grades, the cruise control was having to pull throttle wide open to make it up minor hills. In two occasions, had back firing occur, or firing through the exhaust. Your suggestions please.
Jim Thompson Thomson GA. 75 Avion
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Jim,
As they say, it is probably either spark or fuel.
Spark
My first thought was that is it too retarded. But why? Spark does not jump around sitting in the back yard. Pinging make me think it is too advanced and that is the opposite diagnosis.
Years ago a friend had a vacuum advance diaphragm go out. It caused the engine to run awfully bad. Pull the hose off the distributor. YOu can plug it with a golf tee or something to keep too much air from foiling the test.
Without vacuum you will have a very retarded spark. That should stop the pinging but may also leave you with no power. But if it idles and runs better when you rev it out of gear that might tell us something.
I know you don't want to hear this, but if the timing is moving, it may be the timing chain jumping a cog. If so, it will do it again. Not good news, I know.
Fuel
It could be that the choke is hanging or the quadrajet is dumping fuel for some reason. If so, that could cause a ping like knock if it got too sooted up. A test for this would be to have someone follow and see if you are belching out black smoke when pulling at medium and fuller throttle.
YOu could also pull a couple of plugs to see if they are black and coated with carbon.
You said the choke is releasing some, but it is worth a look, to make sure it is 100% open when warm. Check the heating tube warming the choke.
Let's hope it is something simple.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
[Updated on: Sun, 03 January 2010 17:15] Report message to a moderator |
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| Re: [GMCnet] Need some advice [message #69498 is a reply to message #69476] |
Sun, 03 January 2010 17:15 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Jim,
First thing to do is check your fuel filter(s). The one in the inlet to the
carburetor and any added ones.
My suggestion, whether you find one plugged or not, is to install an in-line
filter between the fuel tank selector valve and the fuel pump, and remove
the one in the carburetor. Fact is, I personally would install one in each
of the tank lines before the selector valve, but that's my typical belt 'n'
suspenders approach.
There have been a LOT of reports lately of filter blocking because of the
ethanol-loaded fuel and its side effects, including "coagulation" when mixed
with water and sloughing off of old tank & line deposits because of it's
scouring.
If that doesn't correct the problem, you might want to get a fuel pressure
gauge (typically a combination vacuum/fuel pressure gauge) and check the
pressure at the carburetor. About 5 psi should be there.
If that doesn't identify a problem, don't tinker with the carburetor: Check
the ignition; it's much less "black magic" than the carburetor.
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
On Sun, Jan 3, 2010 at 3:28 PM, James Thompson
<tjamessherry@bellsouth.net>wrote:
>
>
> Got in our 75 Avion before Christmas to go to my sons house in IL. On
> starting out found when going up slight grades, the cruise control was
> having to pull throttle wide open to make it up minor hills. In two
> occasions, had back firing occur, or firing through the exhaust. Turned
> around and came back to town. While driving in town, could hear major
> pinging when I took off from stop lights. Preignition. I left MH here and
> took my sons Tahoe for the trip. I am back home and have pulled top off
> HEI, the advance moves fine both mechanical and vacumn, When starting and
> idling while warming up, I get black smoke and black suet on the ground out
> of the exhaust. Warms up, choke comes off and it starts and idles ok, but
> appears rich until choke comes off. Idles a little rough with the choke on,
> but no major problem. Need some suggestions for directions to go. It is
> 455 engine, carb, HEI ignition. Have not had problem last fall when I drove
> and have driven into Augusta seve
> ral times last fall with no problems. Unit has been sitting in back yard,
> I start on weekly basis and warm up. Filled with gas just few days before
> starting on on the trip. Your suggestions please.
>
> Jim Thompson Thomson GA. 75 Avion
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Need some advice [message #69506 is a reply to message #69476] |
Sun, 03 January 2010 17:42 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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""Got in our 75 Avion before Christmas to go to my sons house in IL. On starting out found when going up slight grades, the cruise control was having to pull throttle wide open to make it up minor hills. In two occasions, had back firing occur, or firing through the exhaust. Turned around and came back to town. While driving in town, could hear major pinging when I took off from stop lights. Preignition.""
Major pinging is a very bad thing! There are 3 things that cause that--advanced timing. very lean fuel mixture, and extreme overheating. I think there are enough suggestions here to check any of them. Don't trust the temp gage--check for adequate coolant and coolant flow.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Need some advice [message #69519 is a reply to message #69506] |
Sun, 03 January 2010 18:29 |
bukzin
Messages: 840
Registered: April 2004
Location: North California
Karma: 0
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My buddies coach had a problem of running well sometimes
and very poorly on other drives.
After checking out most everything else
it turned out to be a warn distributor.
Went to NAPA and all was well.
Bukzin
1977 Palm Beach
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| Re: Need some advice [message #69528 is a reply to message #69519] |
Sun, 03 January 2010 19:37 |
klassic kampers
Messages: 93
Registered: July 2008
Location: greer,s.c./ellijay,ga
Karma: 0
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the symtoms are contradictory......normally pinging if fuel related is lean............backfiring out the exhaust is rich....... could be the main well plugs(on the carburetor)have gotten very loose and is dumping a major amount of raw fuel into the combustion chamber and causing the mixture to ignite at the incorrect time.........also a cracked inlet manifold could also cause this as I had a GMC come in with similar symtoms as yours... the intake was cracked into the floor below the secondaries, exhaust heat was boiling unmetered fuel over from the float bowl into the venturies flooding some cylinders while other cylinders were lean from the excessive exhaust heat being inhaled.......it was actually blowing or burning the the thick carb base gasket and the carb was loose on the intake..........take the carb off and take a good look at the main well plugs.........while it's off look for cracks in the intake floor........
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the fresh fill up if with ethanol blended feel can cause problems if the existing fuel was a year old...I really have experience with this scenerio on several vehicles in that being a fresh fill up with 90/10 mix in a tank of old gasoline..........I have photos on the gmc site about this......
check the timing chain for play by taking a pull bar and moving the crank pulley one way until you feel the valve spring resistance, mark the pulley and then move the other way until valve spring resistance is felt again....should be 1/2 inch or less but I've seen these engines seem to run fine with 1" of play..........this test is easier to do on a cold engine...
good luck and keep us advised.............
Mike Stewart
1973 GMC 26' Canyonlands /
1973 B.S.A. B50 street tracker-----
Greer,S.C/Ellijay,Ga
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| Re: Need some advice [message #69548 is a reply to message #69519] |
Sun, 03 January 2010 21:18 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| bukzin wrote on Sun, 03 January 2010 16:29 |
... it turned out to be a warn distributor.
Went to NAPA and all was well.
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While a off the shelf "new" distributor should work better than a badly worn stock distributor, it will not have the correct advance curve for our application. I got a "new" distributor for my '73 from Dick Patterson at Springfield Ignition. <http://www.springfield-ignition.com/>
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: Need some advice [message #69643 is a reply to message #69638] |
Mon, 04 January 2010 20:13 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| docsdad wrote on Mon, 04 January 2010 18:33 |
Thanks for all the suggestions. I found carb kit for MH from Walker and purchased at Oreily Auto. Included all specs for setting for MH. I did find one vacumn line leak which may have been part of the problem. Also when I took carb apart, one of the small pipes in the top of carb fell out. It was either out before I took apart, or came out as I lifted top off. My manifold does not look like the ones I see on other GMC's. It appears to have a vacumn controlled EGR valve on driver side of manifold and the PO has modified the air cleaner to fit around it. In addition the engine cover has been raised in the center to allow clearance for the air cleaner. Any suggestions as to what is different. I see in PO data I have that the engine was rebuilt in Canada at 15000 mile mark. May have something to do with this. Thanks to all and I will report back when I get carb back on.
James Thompson 75 Avion
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Sounds like you have a car intake on there because of the EGR valve. The GMC had a block off plate for the EGR. If it is a Toronado intake it will be the low type. if it's from another Olds, it will be too high for the stock engine cover regardless of the EGR. See if you can find some casting numbers and we'll find out what it is.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Need some advice [message #69644 is a reply to message #69643] |
Mon, 04 January 2010 20:17 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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I need to add another comment about the EGR valve. Olds EGR's are notorious for sticking open and they are also notorious for pinging if the valve is stuck. I would take it off--however you would need to find a blocking plate.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Need some advice [message #69646 is a reply to message #69643] |
Mon, 04 January 2010 20:41 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Well I stand corrected by a very knowledgeable member. Although the 403's had block off plates, the original 455 GMC apparently had no EGR provisions. Regardless, it looks like you do have a pasenger car intake. The next question then is leave it? disable the egr? or get a "correct" intake.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Need some advice [message #69647 is a reply to message #69644] |
Mon, 04 January 2010 20:43 |
Ron
Messages: 250
Registered: February 2004
Location: Conifer, Colorado
Karma: 0
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Hi All..
Another comment... If the choke is sticking even a little it will prevent the secondaries from opening thus the low power..
Ron
now a P.O.
Conifer, CO
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| Re: Need some advice [message #69649 is a reply to message #69476] |
Mon, 04 January 2010 21:17 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The EGR manifold is wrong, but shouldn't cause the probelms you list. I'd check the choke, choke pull off and the vac hose that goes to it first (1" long) As mentioned if the choke is not 100% open and you step into the secondaries with a warm engine you will get black smoke due the the secondary air valve lockout. The black smoke kind of rules out fuel filter clog to me.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Need some advice [message #69665 is a reply to message #69646] |
Mon, 04 January 2010 23:36 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Bob, I believe Jim K. had some of those EGR block off plates. At one of the rallies I saw two different types of plates on Jim's table. One was for the Choke heater and one was for the EGR.
Also at a different rally Dick Paterson donated an Intake manifold for the drawing. I noticed it had the EGR port and a new plate over it. I asked Dick about it and he said it came off of a Toronado.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Need some advice [message #69823 is a reply to message #69476] |
Wed, 06 January 2010 16:36 |
docsdad
Messages: 32
Registered: May 2008
Karma: 0
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Member |
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Ran in town drive trial today. Ran good, started ok both hot and cold. Tomorrow out on the interstate for a trial run to see if problem gone. Checked timing it is running at 6 degree BTDC instead of 8 degree per manual at 1100 rpm. Reset idle at 750. May need to adjust choke tomorrow as I may have it a bit lean. Still get some black out of exhaust when first starting up so choke runs it a bit rich. Will see how it handles the hills tomorrow.
James Thompson 75 Avion
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