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Roadrunner won't charge 12.2 volts

Gregg DeGeorge

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Hello ,put together a 68 383 4spd roadrunner its in primer ready for temp plates ,last problem can't get car to charge only 12.2 at battery with car running or off ,tried to different alternators,changed voltage regulator ,battery is new ,tried bypassing alt gauge made no difference so I hooked gage back up.Also checked fuseable link that goes from stater relay to
Bulkhead connector it also a little over 12.2 volts ,voltage regulator grounded to firewall bare metal. ,have engine grounded with strap to firewall ,negative cable has trace wire grounded to radiator support,car was off the road 10 years before I bought it ,harness is in good shape any suggestions welcome thanks Gregg

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Not saying this is your problem, but worth consideration. Don't assume that just because the battery is new, that it is good. Not a common problem, but I have had more than one "new" battery with a dead cell right off the shelf. Wouldn't hurt to test it.
 
Check grounds could have voltage drop....



Pull the green field wire off at the alternator, turn the key to run. @ measure battery voltage at both field terminals. Now take a clip lead and ground the alternatorterminal.....

Do a output check of alternator..
Do not do test to long can cause damage . Run engine @1500 to 2000 rpm..voltage should increase to 15/16.
 
a thought only if you have another battery to use and then see what the output is if other battery shows more charge then it could be a bad cell in the new battery. if it shows the same then full field alt and see what output is. if the volts jump up to 15 volts i would say your alt is fine and continune to look. next question is pulley size on alt or other pulleys are they the correct ones. with the car running and you pull the ground wire off the battery does the voltage jump up or drop down. some thoughts i'm sure somebody else can give you a better way or idea on whats wrong
 
With the engine running, measure the voltage on the IGN side of the voltage regulator and battery - terminal.
You might read more there, which in turn will regulate alternator output down as the voltage is good.
This has nothing to do with a broken regulator, but it can be you have some serious voltage losses in the wiring towards the bulkhead connector and battery.
I had similar issues but mine was overcharging, caused by the fact that the regulator only had 11V on the input side and always kept the alternator charging while it was not needed.
All bad contacts in the wiring caused this and after a good clean up of connectors and grounds it improved a lot.
 
Check grounds could have voltage drop....
What do you mean measure field wire ,I only have one on alternator think the other end goes to voltage regulator ,I did run an extra ground wire from voltage red to engine block no change ,also tried grounding body of alternator no change ,also with car running pulled the positive cable car died right away just a little lost never had such a hard time ,tried to get alternator tested at advance kid couldn't get it set up ,might just try another one


Pull the green field wire off at the alternator, turn the key to run. @ measure battery voltage at both field terminals. Now take a clip lead and ground the alternatorterminal.....

Do a output check of alternator..
Do not do test to long can cause damage . Run engine @1500 to 2000 rpm..voltage should increase to 15/16.
 
Check....Pull the GREEN field wire off at the alternator, and put a clip lead on the alternator terminal to ground. Your checking the field, if wiring is OK, the charging circuit is OK, the voltage at the battery will immediately jump higher voltage. Watch the RPM and do NOT allow the voltage to go above about 15V. you are doing a “full field” test, and causes the alternator to go to full output.....

check if this works check voltage reg...
 
I had your same problem happen to me and it turned out to be the msd high torque mini starter had gone bad and was drawing current (all after only 2500 miles and less than 100 starts). Not a hair width between the starter housing and exhaust though...
 
My alternator is reading about 13.3 V at idle. From what I read it should be in the 14.5 range. It was mentioned above that the field wires should each show a voltage near 12. I've also read that one should be 12 and the other will vary. I have one measuring 12+V and 4+V. Does that mean I have an issue and if so where? Engine compartment was completely disassembled and put back with new wiring harness, new alternator, new battery but old regulator. Just tried new regulator and alternator went to 13.9 and the field wire voltages are now 14+V and 5+V. Been driving it weekly for about 2 months and had trouble cranking today after a short drive. Dash voltmeter is in the normal range at idle but always up on cruise throttle. Does bounce with the blinker on when at idle. Thanks
 
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You might want to separate the bulkhead connectors and check the condition of all male/female terminals. It is possible that the fusible ling terminal is burnt inside...and could lead to a voltage loss.
 
At idle it is quite normal to see a lower voltage, also depends on what is demanding charging power.
Measure again while holding the rpm up at around 2000 rpm and you might see an increase to 14.4 volt.
Field wire voltage will vary, depending on conditions if the alternator needs to be trigger to charge or not.
Regarding the dash meter you are talking about must be the Amp meter right? Originally there should be no volt meter.
The amp meter will swing about when the blinker is on because of the intermittent power consumption of the indicator lights.

What Kiwi recommends is also a good one to look out for and make sure the bulkhead connectors are in good shape so no losses are caused there.
You wrote you changed the harness so i guess this wil be ok but if not it is worth a clean up.
 
Yes amp meter, my bad. Everything seems to check out. Wondering if it's not starter solenoid or starter. I leave the car sit for week or two and it cranks fine, plenty of battery. After a drive when it's good and hot if I turn it off and then restart in a short time period it acts like low/dead battery. Leave it sit for a few hours and it cranks fine. Seems heat related.
 
Did you measure the battery voltage prior to starting the car when its "hot"?
If the battery voltage is ok it might be the starter suffering from "heat soak" and draw excessive amps to crank the engine and the battery is struggling with it?
If it does start in the end the battery should be having enough juice to give what it takes, but the starter might be on the way out?
 
I just went through something similar regarding the cold start/hot start.
Relocated the battery cable ground (to the engine)to another ground point on the engine and it solved the problem.
 
I just went through something similar regarding the cold start/hot start.
Relocated the battery cable ground (to the engine)to another ground point on the engine and it solved the problem.

And how does that relate to the issue of poor starting when hot?
Originally it is bolted on the cylinder head which is the hottest area of the engine i guess, but the rest of the engine will be similar temperature after standing still for some time.
 
And how does that relate to the issue of poor starting when hot?
Originally it is bolted on the cylinder head which is the hottest area of the engine i guess, but the rest of the engine will be similar temperature after standing still for some time.

In my case I had the battery ground wire attached to a bolt on the AC bracket...I relocated the cable end to the cylinder head. Regarding the relationship or why it solved the problem is something I have no answer for... all I know is it worked. I've come the conclusion these old cars each have a personality and quirks of their own. :)
 
Hello ,put together a 68 383 4spd roadrunner its in primer ready for temp plates ,last problem can't get car to charge only 12.2 at battery with car running or off ,tried to different alternators,changed voltage regulator ,battery is new ,tried bypassing alt gauge made no difference so I hooked gage back up.Also checked fuseable link that goes from stater relay to
Bulkhead connector it also a little over 12.2 volts ,voltage regulator grounded to firewall bare metal. ,have engine grounded with strap to firewall ,negative cable has trace wire grounded to radiator support,car was off the road 10 years before I bought it ,harness is in good shape any suggestions welcome thanks Gregg

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I don't see anywhere in the OP's original post where he had a hot cranking issue. I thought it was a low charging voltage issue. Where did that problem come from?
 
Post #12....not the OP but mentioned the ground hot/cold issue. Didn't mean to redirect conversation.
 
So latest update, after I replaced the voltage regulator I finally got a chance to drive the car the last two days. No issues with starting when hot, although the weather has tuned colder. Still think it's a starter issue along the lines of what Wietse mentioned above. Since the new regulator seems to be sending more charge to the battery perhaps that was enough to give the battery the extra it needs. Doesn't appear to be a charging issue so I'll move to a new/different thread going forward. Don't want to hijack this one. Thanks to everyone for your input.
 
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