Low Cranking Voltage

R

rmcmorran

New member
Ok. Here's the situation. I have a 77 Scout II with a 345 and new 140 amp delco 12si. Electrical components are: 3 cooling fans, alarm, radio, and ARB compressor. It also has a Holley commander 950 TBI system, which is what I'm having a problem with. It also has a brand new optima red top but my cranking voltage is low, around 10. I've been having idle issues for years now and have been told by several people that the low cranking voltage is likely causing issues with iac but I can't figure out what's causing the low cranking voltage. The battery is fully charged and the alternator is putting out about 14.2v. I have checked and cleaned the grounds and the wiring is new, heavy gauge, marine grade stuff. Also, when the engine is cold the motor cranks for about 10 seconds then starts and idles perfect at 650 rpm. If I drive around for awhile and then put it in park or neutral it idles at anywhere from 900 to 1300. When I turn it off and restart it, if it starts right away it idles high. If I immediately shut it off again it doesn't restart right away (cranks for about 10 seconds again) and idles fine.

All that being said, I need some help figuring out the low cranking voltage situation.
 
Somewhere you are getting a voltage drop.

How many amps is the starter taking when you go to start? If it is more than 200 amps you have a bad starter, bad connections between the battery and starter, or a bad battery.

I recently went through the same issue with one of my rigs. When started the alternator was putting out 14.2 volts. When the engine was stopped the battery showed 12.8 volts. Within ten minutes the hotel load was enough to drop the battery to 10.6 volts. When I went to start with the low voltage it pegged the amp meter.

Since every electrical system depends on the battery that would be the first place I would check to determine the problem. Have your battery checked with a carbon pile type of load tester. If it can't handle a load then it is time to get a new battery. I have heard that optima has been having problems with their red tops recently.

Remember, just because something is new it doesn't mean you can't still have problems.
 
This is voltage @ the battery terminal center I assume?

I too have been hearing stories about optima batteries. I only use standard flooded cell battery's and have had good service from them.

Yea 10 volts is not desired but fairly common on a big direct drive starter engine.
 
Yeah, measured at the battery. I just had the starter bench tested and it passed. If that much of a voltage drop is normal then I'm gonna have to figure out a way to reduce it. Maybe a gear reduction starter. Load testing the battery tomorrow.
 
What about a dual battery set up? Can I put the accessories and ecu on a seperate battery so they aren't affected by the voltage drop when it's cranking?
 
Almost anything is possible if you spend enough $$$.

Even though the Scout and Scout II's were never known for their wonderful electrical systems, if everything is up to par you shouldn't be having such a drop in voltage. Something somewhere between your battery and your starter something is sucking up your volts.

I would still tend to say the problem is at the head of the stream--at the battery. I think that particularly since your starter has been bench tested and found to be okay.

If your battery is tested and found to be within par then there still has to be something inline from the battery to the starter that is sucking up volts.

You have plenty of alternator to run all of your components. Even at idle with everything on I doubt you would be using more than the alternator is putting out. So I think you can forget about that part of the equation.

You May want to consider installing a Ford type remote start relay. Your voltage drop May be occurring as your start circuit goes through the bulkhead connector on the firewall.

Good luck.
 
Thanks. I will get the battery tested this week. It has a new wiring harness so no more bulkhead connectors. The starter has three wires on the hot terminal, one goes straight to the battery, one is the solenoid power, and the other goes to the ARB compressor which has a relay.
 
Just a little interjection

December 2009 I put a red top optima battery in and have had bad luck with it sense day 1. Just like you said, my batter also seems to like 10 volts instead of 12 volts. When I put the battery charger on it some times it charges and some times the battery chargers red light comes on indicating a bad battery. So I don’t like my red top optima, im looking to ditch it…..
 
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