Chasing my tail looking for a problem

[J_F250]

OK guys here it goes: Recently been having a hard time starting my truck. It seems like the batteries were low and not charging. Went to parts store to test batteries and alternator. Batteries tested good. Alternator did not get tested properly, but they said it was good. (Left it on truck, instead of me taking it off.) Fast forward 2 weeks later...last Friday go run an errand at work and get back...put the truck in park...revs up to like 1800rpm and goes back down...OD light starts flashing..take it to the dealer..OSS code in the tranny. Tuesday replace OSS and still doing it...take it to the dealer and they tell me that I have one bad battery and the other might possibly be. Take it to store where I purchased them and take them off..they take them to the warehouse (the batteries are Interstate Megatron Plus) and they test them and they say they are good.
I thought about replacing the battery cables because they have seen better days..not the wires themselves but the terminals need good nuts and bolts..and the terminals are a little beat up and seem to be really soft metal (if you put jumper cables on them it leaves an indention of the jaw marks). I have heard from a buddy that the OSS code could be caused by anything in the charging system not being up to snuff...
What do you guys suggest? Can I just buy the cables at autozone or do I need OEM cables?
I am about to lose my mind here. Any other suggestions? I plan on taking the alternator off today and taking it to Advance and let them test it.
Where do I go from here?

[Tail_Gunner]

Definately sounds like a electrical problem. Specifically, I think you might be on the right track with the cable connections. I'd start looking at things like corroded battery connections and the ground cable connections at the block & frame. The ground connections at the block are an often over looked cause of starting & electrical issues. Frequently they get a little corroded, greasy or oily.

[BIG JOE]

X2 on what TG sez, and there are many Ground wires along the inner fender and radiator support areas that independently ground specific components also. Back them all off and clean them up too. Many times, just backing them off and re-tightening them works ?

Joe

[Potentialbuyer]

You can test your cables and all the connections by using a DVOM. You are not going to be looking for available voltage by connecting the meter from positive to negative . You need to look for voltage drop on the power and ground sides by connecting the meter from positive to positive and negative to negative. This may sound confusing but voltage drop testing is the best way to diagnose electrical circuits. Voltage drop testing is better because you are testing the circuits under load. If you think there is a problem with your positive or negative cables, you need to test them for drop. Take your meter and set it to DC volts. Put the red lead on the center of the battery positive terminal and then put the black lead on the bolt at the alternator where the charging wire goes. Start the vehicle and turn on several electrical accessories (lights, blower on high, wipers, etc). Read your meter and it should read less than .5 volts. If you read more than that, your positive charging wire has excessive drop and that may be why your charging system is not working correctly. Think of if this way-should you read voltage on only one side of the circuit? No because the voltage is supposed to be going through the wire to the load in the circuit. If you read voltage, you are reading the voltage that is lost (dropped) on that side of the circuit because of a bad connection or high resistance. You can test for drop on the negative side the same way. Red lead on the center of the battery negative terminal and the black lead on the bolt for the ground wire on the engine block. Have someone crank the engine and you should read less than .2 volts on your DVOM. If you read more than .2 volts you have a bad connection somewhere in the ground cable circuit. The problem can be isolated by keeping the red lead on the center of the battery terminal and working the black lead back towards the battery at each connection. When your voltage drop is acceptable (.2V for negative, .5V for positive) as you work your way back to the battery, you found the problem was in the connection before the good reading. A good example would be if you put your red lead on the battery positive post and the black lead on the positive battery cable that is connected to the battery. If you crank the engine and you read 2 volts, this means that there is a 2 volt drop in the positive battery terminal connection at the battery. Since your positive terminal has lost 2 volts due to a bad connection, there is only 10 volts left to go to the starter and the vehicle will probably crank slowly. If you take the cable off, clean it, and re-test it, you would find that the reading would be .5 volts or less. So think of this in reverse for your charging system. If there is excessive drop in any of your cables or connections, the voltage that is supposed to charge the battery is lost (dropped) and there isn't enough left to charge your battery. On the other hand, if you can't find any drop in any of the charging circuits (positive or negative), there may be a problem with the components (alternator, ect). This may sound very confusing but if you research "voltage drop" on your computer, you will probably find a better explanation for this procedure than I have attempted to do here. If you can master voltage drop testing, you will be considered the electrical guru and people will come from miles away for you to fix their electrical problems. Good luck-Gil

[Dogman]

I had the same problem, I chaced the problem for three weeks. Ended up being the alternator not charging right. The dealer did a test and found out what it was. I had dash light coming on and all that.

[J_F250]

Originally Posted by Potentialbuyer

You can test your cables and all the connections by using a DVOM. You are not going to be looking for available voltage by connecting the meter from positive to negative . You need to look for voltage drop on the power and ground sides by connecting the meter from positive to positive and negative to negative. This may sound confusing but voltage drop testing is the best way to diagnose electrical circuits. Voltage drop testing is better because you are testing the circuits under load. If you think there is a problem with your positive or negative cables, you need to test them for drop. Take your meter and set it to DC volts. Put the red lead on the center of the battery positive terminal and then put the black lead on the bolt at the alternator where the charging wire goes. Start the vehicle and turn on several electrical accessories (lights, blower on high, wipers, etc). Read your meter and it should read less than .5 volts. If you read more than that, your positive charging wire has excessive drop and that may be why your charging system is not working correctly. Think of if this way-should you read voltage on only one side of the circuit? No because the voltage is supposed to be going through the wire to the load in the circuit. If you read voltage, you are reading the voltage that is lost (dropped) on that side of the circuit because of a bad connection or high resistance. You can test for drop on the negative side the same way. Red lead on the center of the battery negative terminal and the black lead on the bolt for the ground wire on the engine block. Have someone crank the engine and you should read less than .2 volts on your DVOM. If you read more than .2 volts you have a bad connection somewhere in the ground cable circuit. The problem can be isolated by keeping the red lead on the center of the battery terminal and working the black lead back towards the battery at each connection. When your voltage drop is acceptable (.2V for negative, .5V for positive) as you work your way back to the battery, you found the problem was in the connection before the good reading. A good example would be if you put your red lead on the battery positive post and the black lead on the positive battery cable that is connected to the battery. If you crank the engine and you read 2 volts, this means that there is a 2 volt drop in the positive battery terminal connection at the battery. Since your positive terminal has lost 2 volts due to a bad connection, there is only 10 volts left to go to the starter and the vehicle will probably crank slowly. If you take the cable off, clean it, and re-test it, you would find that the reading would be .5 volts or less. So think of this in reverse for your charging system. If there is excessive drop in any of your cables or connections, the voltage that is supposed to charge the battery is lost (dropped) and there isn't enough left to charge your battery. On the other hand, if you can't find any drop in any of the charging circuits (positive or negative), there may be a problem with the components (alternator, ect). This may sound very confusing but if you research "voltage drop" on your computer, you will probably find a better explanation for this procedure than I have attempted to do here. If you can master voltage drop testing, you will be considered the electrical guru and people will come from miles away for you to fix their electrical problems. Good luck-Gil

Good post...I did not know this. Thanks.

[JLDickmon]

Originally Posted by Potentialbuyer

You can test your cables and all the connections by using a DVOM. You are not going to be looking for available voltage by connecting the meter from positive to negative . You need to look for voltage drop on the power and ground sides by connecting the meter from positive to positive and negative to negative. This may sound confusing but voltage drop testing is the best way to diagnose electrical circuits. Voltage drop testing is better because you are testing the circuits under load. If you think there is a problem with your positive or negative cables, you need to test them for drop. Take your meter and set it to DC volts. Put the red lead on the center of the battery positive terminal and then put the black lead on the bolt at the alternator where the charging wire goes. Start the vehicle and turn on several electrical accessories (lights, blower on high, wipers, etc). Read your meter and it should read less than .5 volts. If you read more than that, your positive charging wire has excessive drop and that may be why your charging system is not working correctly. Think of if this way-should you read voltage on only one side of the circuit? No because the voltage is supposed to be going through the wire to the load in the circuit. If you read voltage, you are reading the voltage that is lost (dropped) on that side of the circuit because of a bad connection or high resistance. You can test for drop on the negative side the same way. Red lead on the center of the battery negative terminal and the black lead on the bolt for the ground wire on the engine block. Have someone crank the engine and you should read less than .2 volts on your DVOM. If you read more than .2 volts you have a bad connection somewhere in the ground cable circuit. The problem can be isolated by keeping the red lead on the center of the battery terminal and working the black lead back towards the battery at each connection. When your voltage drop is acceptable (.2V for negative, .5V for positive) as you work your way back to the battery, you found the problem was in the connection before the good reading. A good example would be if you put your red lead on the battery positive post and the black lead on the positive battery cable that is connected to the battery. If you crank the engine and you read 2 volts, this means that there is a 2 volt drop in the positive battery terminal connection at the battery. Since your positive terminal has lost 2 volts due to a bad connection, there is only 10 volts left to go to the starter and the vehicle will probably crank slowly. If you take the cable off, clean it, and re-test it, you would find that the reading would be .5 volts or less. So think of this in reverse for your charging system. If there is excessive drop in any of your cables or connections, the voltage that is supposed to charge the battery is lost (dropped) and there isn't enough left to charge your battery. On the other hand, if you can't find any drop in any of the charging circuits (positive or negative), there may be a problem with the components (alternator, ect). This may sound very confusing but if you research "voltage drop" on your computer, you will probably find a better explanation for this procedure than I have attempted to do here. If you can master voltage drop testing, you will be considered the electrical guru and people will come from miles away for you to fix their electrical problems. Good luck-Gil

Gil, that's the best description I've ever seen outside of a textbook on how to do that..

[Potentialbuyer]

I was a Ford instructor for 8 years and this concept was one of the most difficult things to get the technicians to understand. Once you get it, electrical diagnosis becomes easy. No more "parts 'till it starts!" Gil

[J_F250]

I got the problem fixed....I'm a little embarrassed to admit it but it was a loose battery terminal.
Thanks guys for the help.

[iracemine]

sweet knowledge! Thanks for the how to, I am sure to be using it from now on.