97 7.3 Voltage Swing - Ford Powerstroke Diesel Forum
 
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post #1 of 7 Old 06-06-2019, 10:52 AM Thread Starter
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Question 97 7.3 Voltage Swing

Have had this problem for years, voltage swing from 14 - 14.7 v while running, engine runs smoothly, but you can see the swing corresponds to engine/belt movement. Alternator good, all new batteries and cables, rebuilt standard swamp's injectors about two years ago, new ford idler pully and tension pully. Looking for a clue as to what would cause this and how to diagnose.
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post #2 of 7 Old 06-07-2019, 03:47 AM
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How are the connectors going to the alternator? Any loose wiring?

Also how old is the glow plug relay?
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post #3 of 7 Old 06-07-2019, 05:02 AM Thread Starter
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Replaced glow plug relay when I replaced injectors and glow plugs. Have the power lead to the relay disconnected, summer in FL, no need for glow plugs, did not matter when connected or not, still can see swing on analog and digital voltage. Wiring to alternator appears to be solid, will start it up and play with the harness to see if that makes any difference.
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post #4 of 7 Old 06-08-2019, 08:25 PM
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Quote:
Originally Posted by PalmettoJoe View Post
Replaced glow plug relay when I replaced injectors and glow plugs. Have the power lead to the relay disconnected, summer in FL, no need for glow plugs, did not matter when connected or not, still can see swing on analog and digital voltage. Wiring to alternator appears to be solid, will start it up and play with the harness to see if that makes any difference.


I had something similar, not voltage swings but intermittent battery light on the dash with good voltage. Tried to replicate it by messing with the wiring harness. Couldnít duplicate. Eventually just replaced both wiring pigtails on the alternator and it hasnít happened since. They are cheap. You could probably buy both for under $10, maybe $40 if you went straight oem.


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post #5 of 7 Old 06-24-2019, 10:58 AM Thread Starter
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Good news, replaced alternator pigtails, used solder seal to make connections (old one was crimped on), no more voltage swings, running at a steady 13.6 V at 80 mph.
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post #6 of 7 Old 06-24-2019, 08:26 PM
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Well good. That seems to be a common problem on these trucks with their age. At least itís a cheap fix. Glad you got it working again.


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post #7 of 7 Old 06-25-2019, 02:52 AM Thread Starter
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Thanks, the one I replaced had been a crimped connection, surprised this does not show up in these threads, could not find a similar problem and solution. Now at least others will have one conclusion. Too many times on these forums, I see people throwing parts at problems, not diagnosing. Oh, well on to the front seal oil leak.
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1997 , 7.3l , steady , swing , voltage

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