| Starting Problem [message #108407] |
Mon, 13 December 2010 05:22  |
Mark of Excellence
Messages: 18
Registered: December 2010
Karma: 0
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Junior Member |
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My GMC all of a sudden will not crank over with the battery switch in normal mode. Once I switch over to boost it starts up fine. I have new batteries, cables, and good grounds?
Benson
76' Birchaven
Florida
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| Re: [GMCnet] Starting Problem [message #108408 is a reply to message #108407] |
Mon, 13 December 2010 05:37  |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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you should never have to use the Boost switch, for starting.
read this set of slides ,
http://www.gmcmhphotos.com/photos/showgallery.php?cat=5493
http://goo.gl/B2PLG
it may be as simple as re-routing your battery cables because of poor
connections
gene
On Mon, Dec 13, 2010 at 3:22 AM, Jamison <Birchaven76@aim.com> wrote:
>
>
> My GMC all of a sudden will not crank over with the battery switch in
> normal mode. Once I switch over to boost it starts up fine. I have new
> batteries, cables, and good grounds?
> --
> Jamison
> 76' Birchaven
> Vagabond, FL
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
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>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: Starting Problem [message #108414 is a reply to message #108407] |
Mon, 13 December 2010 06:15 |
Mark of Excellence
Messages: 18
Registered: December 2010
Karma: 0
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Junior Member |
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I have another piece of information that may help. When the battery switch is in normal mode I have no 12V power at the dash. None of the warning lights come on, no nothing. It is like the ignition switch is not getting any power. But on boost mode the dash lights up like a Christmas tree and the starter cranks over like a champ. Could it be a bad battery relay or the isolator under the hood?
Benson
76' Birchaven
Florida
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| Re: Starting Problem [message #108417 is a reply to message #108407] |
Mon, 13 December 2010 06:56 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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From St Petersburg RU---It would not be the isolator. That would just cause a charging problem. (I'm assuming both and especially the engine battery are full charged and you are not mistaken on the engine battery being fully charged.) The Boost switch should just parallel the house batt on top of the engine batt. Unless that solenoid switch has failed in some wierd mode, I would blame a connection that "looks good but is bad". If you turn on say the headlights in non boost mode and they do not come on, then you can take a VOM on 20VDC scale and meter across all the connections at the engine battery and the grounds and the boost switch. When you find about 12V that is the bad connection as it should be 0V. Note that the enigine battery could be bad internally with a bad cell jumper. I would wear saftey glasses when doing probing around the battery as a jiggled bad may make connection and could spark. An internal battery defect can cause a violent explosion. I once turned the key on a truck that had an internal intermittant in the crank battery and the thing exploded revieling all the internals... and the acid. If you have a load type battery tester you could test the presumed good engine battery for actual current delivery.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Starting Problem [message #108421 is a reply to message #108407] |
Mon, 13 December 2010 07:54 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| Mark of Excellence wrote on Mon, 13 December 2010 06:22 |
My GMC all of a sudden will not crank over with the battery switch in normal mode. Once I switch over to boost it starts up fine. I have new batteries, cables, and good grounds?
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| Mark of Excellence wrote on Mon, 13 December 2010 07:15 |
I have another piece of information that may help. When the battery switch is in normal mode I have no 12V power at the dash. None of the warning lights come on, no nothing. It is like the ignition switch is not getting any power. But on boost mode the dash lights up like a Christmas tree and the starter cranks over like a champ. Could it be a bad battery relay or the isolator under the hood?
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Jamison,
As you describe the problem, there is only one possible issue.
A single point failure of a connection in the starting battery circuits.
Go looking for a loose or bad connection to the new starting battery.
It cannot be the boost contactor or the primary relay or the isolator and still do as you describe.
Good Luck
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: Starting Problem [message #108446 is a reply to message #108421] |
Mon, 13 December 2010 10:55 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| mcolie wrote on Mon, 13 December 2010 07:54 |
| Mark of Excellence wrote on Mon, 13 December 2010 06:22 |
My GMC all of a sudden will not crank over with the battery switch in normal mode. Once I switch over to boost it starts up fine. I have new batteries, cables, and good grounds?
|
| Mark of Excellence wrote on Mon, 13 December 2010 07:15 |
I have another piece of information that may help. When the battery switch is in normal mode I have no 12V power at the dash. None of the warning lights come on, no nothing. It is like the ignition switch is not getting any power. But on boost mode the dash lights up like a Christmas tree and the starter cranks over like a champ. Could it be a bad battery relay or the isolator under the hood?
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Jamison,
As you describe the problem, there is only one possible issue.
A single point failure of a connection in the starting battery circuits.
Go looking for a loose or bad connection to the new starting battery.
It cannot be the boost contactor or the primary relay or the isolator and still do as you describe.
Good Luck
Matt
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Where is the engine battery ground attached? If it is not attached to the engine, move it there.
If the battery is charged, you have to have a bad connection between the engine battery and the starter either on the positive or the ground side. I would be checking and cleaning all of the battery cable connections both at the battery and the engine ends.
If the battery is not charged then you probably have a different problem. Put a volt meter across the engine battery and read it when not starting and when trying to start. If the static voltage is 12.6 or above the battery is charged. If the voltage drops to nothing or very low you have a bad battery.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Starting Problem [message #108448 is a reply to message #108417] |
Mon, 13 December 2010 10:58 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| JohnL455 wrote on Mon, 13 December 2010 04:56 |
From St Petersburg RU--- If you turn on say the headlights in non boost mode and they do not come on, then you can take a VOM on 20VDC scale and meter across all the connections at the engine battery and the grounds and the boost switch. When you find about 12V that is the bad connection as it should be 0V.
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John,
Been fiddling with cars, tractors and things that go all my life, but somehow my small brain never thought of the test you describe. Duh. Oh, well. Live and learn.
Thanks
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Starting Problem [message #108470 is a reply to message #108446] |
Mon, 13 December 2010 13:33 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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On Dec 13, 2010, at 9:55 AM, Ken Burton wrote:
>>
>
> Where is the engine battery ground attached? If it is not attached to the engine, move it there.
>
> If the battery is charged, you have to have a bad connection between the engine battery and the starter either on the positive or the ground side. I would be checking and cleaning all of the battery cable connections both at the battery and the engine ends.
>
> If the battery is not charged then you probably have a different problem. Put a volt meter across the engine battery and read it when not starting and when trying to start. If the static voltage is 12.6 or above the battery is charged. If the voltage drops to nothing or very low you have a bad battery.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
Yes, it might be the engine battery ground or a bad connection at one of the engine battery terminals but it couldn't be a problem at the starter because he said that the starter worked fine when the boost switch was pushed.
Emery Stora
77 Kingsley
Santa Fe, NM
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