Voltage lost when cranking

[maxwell]

Good evening. I am running the Firecore ready-to-run with a MSD box on my 440 68 charger. When cranking from the key I loose 2 full volts from the batter and I am not able to start the car unless I jump the starter relay. I have checked continuity on all wires in the ignition system and battery and they are good. My grounds are good also. any ideas of why I would loose so much when cranking.

 

[HEMI-ITIS]

Sounds like a weak battery.Do a load test.

 

[texas69bee]

Why are you running a RTR distributor with an external ignition box? RTR is set to eliminate the MSD.

 

[maxwell]

Why are you running a RTR distributor with an external ignition box? RTR is set to eliminate the MSD.

Based on the MSD manual, you still have the option to used the 6A box. the box isn't causing the issue as I can see though.

 

[maxwell]

Sounds like a weak battery.Do a load test.

Thank you. I will do a load test today.

 

[PP1RT]

Sounds like a weak battery.Do a load test.

X2. Your battery sounds like it's about done in...

 

[maxwell]

X2. Your battery sounds like it's about done in...

Yeah its a fairly new Autozone Gold battery that I put on a battery tender every now and then. Anyone have issues with theses batteries?

 

[PP1RT]

Yeah its a fairly new Autozone Gold battery that I put on a battery tender every now and then. Anyone have issues with theses batteries?

Batteries are a crap shoot....sometimes they go a long time...sometimes they don't. Just because it's only a few months old doesn't mean a thing...

 

[Bill Monk]

Do a voltage drop test. You need a good voltmeter to do it but I had a relatively new positive cable that showed continuity but was dropping so low under load, the car wouldn't start. If you don't know what I'm talking about, check it out here:
http://www.aa1car.com/library/voltage_drop_testing.htm

 

[moparnation74]

Your still under warranty take it back....I agree they are a crapshoot on which one you get

 

[Ranger16]

ANYTHING from AutoZone is a crap shoot ..............................................with the odds stacked against you.

Kind of sounds like a dead cell to me. The load test will tell.

 

[maxwell]

Battery checked out good. I was told it may be the ignition switch so I replaced it and checked continuity before installing. All was good there. On to the next phase of this gremlin.

 

[bigmanjbmopar]

Wiring, has anything been done to the wiring at the ignition switch? added radio or something? I just went through this on my 69 there is a yellow that goes to the starter relay that gets 12v on it when you crank there is also a brown and blue wires that have to be connected for key on and accessory one of these the brown feeds power to your MSD box and if the ballast resistor was not tied through then you might get this condition, one of the blues is a power tap right off the alternator check these out with a wiring diagram to make sure.

 

[PP1RT]

Battery checked out good. I was told it may be the ignition switch so I replaced it and checked continuity before installing. All was good there. On to the next phase of this gremlin.

Go thru and clean your grounds.

 

[texas69bee]

You said you have to jump the starter relay. I’m assuming you mean short it out. If that’s the case, are you sure the relay isn’t bad?
Also look at bigmanjbmopars post. Is that yellow jumper wire connected?

 

[maxwell]

View attachment 532249 You said you have to jump the starter relay. I’m assuming you mean short it out. If that’s the case, are you sure the relay isn’t bad?
Also look at bigmanjbmopars post. Is that yellow jumper wire connected?

Yelp, the yellow wire is connected. I'm back to investigating the battery. Thinking I have a dead cell. Hasn't charged from the alternator in months.

 

[Wietse]

If it does start by bypassing the relay (shorting) the battery would not be the issue right?
And a voltage drop on the battery is quite normal as it is giving max for cranking the engine.
You could run a bypass and hook up the 12V for the ignition direct to the battery +.
That way you eliminate any contact issues etc.

Not sure if you still have the resistor in place or bypassed/removed.
During cranking the coil gets a 12volt supply from the ignition switch from a brown wire, once running it gets powered by a blue wire direct from alternator through the resistor.

 

[HEMI-ITIS]

Is the battery up front or in the trunk?