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Low Alternator output at idle |
Post Reply | Page 123 4> |
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ddfarm
AMC Nut Joined: Nov/23/2009 Location: Virginia Status: Offline Points: 315 |
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Posted: Apr/30/2011 at 8:10am |
I have searched this topic and found several good threads. But none seem to answer my question. I have a 73 AMX 304 (AT)with a Edlebrock performance package( including cam). My car idles at 1200 rpm out of gear and 700 in gear. This car is a off frame restoration and all connections are clean. The alternator is a 55 amp stock(new). The lights dim at idle(700) and if the rpms remains there for a extended period the lights just cut off. If you put it back in neutral(1200 rpm) the lights come back on. I do have a electronic ign. So I have 2 questions.
1.Is there another alternator that I can get that will put out more at 700 rpms? 2.Why would the light just cut off completely? Then cut back on with more rpms.
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cindys1971
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FuzzFace2
AMC Addicted Joined: Jul/05/2007 Location: Angier, N.C. Status: Offline Points: 10324 |
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1. I dont know but if the ALT puts out the right volts & amps at higher rpm then I would say the ALT side is good but the REG side on the weak side. Recheck ALL grounds and if everything has fresh paint it may not be getting a good ground. You have the ground cable from motor mount bracket to cross member?
2. If I under stand right as volts go down the amps go up. Running at low volts as you say may be over loading the breaker in the head light switch and why the lights go out.
Dave ----
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TSM = Technical Service Manual
75 Gremlin X v8 for sale 70 Javelin 360/auto drag car 70 Javelin 360/T5 Street car |
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ddfarm
AMC Nut Joined: Nov/23/2009 Location: Virginia Status: Offline Points: 315 |
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Thanks Dave. Yes I do have the ground cable from mount bracket to cross member. And it is a good clean connection. The voltage reg is new but I will recheck to see if I have hooked it up correctly. I did not know that the the head light switch had a breaker in it. Now I understand the lights cutting off.
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cindys1971
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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First, we can't diagnose anything until you measure the actual voltage at the battery. Until then we are just guessing about grounds, connections, etc.
55 amp is MORE than enough, even with electronic ignition, which really doesn't take much more than stock, some less (more effecient)
Measure voltage - if it's in the 14v range, then the alternator is fine. If not, then you may have:
bad/worn brushes
worn/burned slip rings
bad diode
bad regulator
bad stator
Your problem is not a 55 amp alternator, you problem is a connection, ground, switch, or problem with the alternator or regulator.
A light switch will cut out much easier once the breaker has tripped a time or two. They are weakened by tripping - IF that's what is happening.
Take voltage measurements at the battery, at the back of the alternator, at the headlights themselves.
Check grounds - good looks doesn't mean good connectivity, and cables can be bad where the wire connects to the cable end - down inside where you can't see.
Measure for voltage drop across connections, too.
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ddfarm
AMC Nut Joined: Nov/23/2009 Location: Virginia Status: Offline Points: 315 |
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Okay, I have checked my grounds at the wiring harness and cross member. There is hardly any resistance at both(voltage is same). I also jumped a ground wire from the battery to the harness. Also jumped a ground wire from the battery to the lights. Also jumped a ground wire from battery to regulator ground. All results were no difference. The lights still dim at idle in gear. Voltage across the battery 13.9 at idle out of gear(1200). 12.8 at idle in gear(800prm). Voltage at back of alternator is same(12.8/800, 13.9/1200). Voltage at headlights is same as other test. Headlights are diffiently dimming due to voltage drop.
Is there another test I can run?
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cindys1971
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ddfarm
AMC Nut Joined: Nov/23/2009 Location: Virginia Status: Offline Points: 315 |
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One additional thing. My AMX has a amp meter in the dash gauges and the meter falls below the middle point when the rpms are dropped below 1200.
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cindys1971
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offroaddodge
AMC Apprentice Joined: Apr/14/2010 Location: kenosha wi Status: Offline Points: 135 |
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the diode is bad that will stop output at low rpms
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Retired 70 Machine Owner
Had to get feet wet again Started Another Chapter Why???????? Bringing life back to 1973 Matador |
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offroaddodge
AMC Apprentice Joined: Apr/14/2010 Location: kenosha wi Status: Offline Points: 135 |
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is that a motorola alt does it have a red bridge on the back that needs to replaced
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Retired 70 Machine Owner
Had to get feet wet again Started Another Chapter Why???????? Bringing life back to 1973 Matador |
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offroaddodge
AMC Apprentice Joined: Apr/14/2010 Location: kenosha wi Status: Offline Points: 135 |
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bad regulator maybe or wrong one
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Retired 70 Machine Owner
Had to get feet wet again Started Another Chapter Why???????? Bringing life back to 1973 Matador |
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poormansMACHINE
AMC Addicted Charter Member Joined: Jun/28/2007 Location: Shoemaker-Levy9 Status: Offline Points: 12302 |
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With a 9% change in voltage, lamps will dim and brighten accordingly.
Pretty normal for the era. |
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