Cat 420d 13v acts like dead batteries

[huzyrdaddy]

Cat would not start last fall. I thought batteries were dead. Cat sat out all winter. June 7, 2018 put in new batteries. First try gave a quick vroom, stop. after that, volt meter in cab shows low voltage, say 6v. will not turn over. just click click click. i have 13v at batteries. with key in power on position, 12v at alternator. 12 v at starter, and in cab voltage shows 6v. what should i test, fix, replace first?

 

[Bls repair]

Check electric connectors both hot and ground

 

[JD955SC]

Battery cables both power and ground plus check ground connections. Also check for loose battery cable terminals. After they’ve been loosened and tightened several times they are done for.

Bad battery cables have high resistance, green corrosion, missing/burned insulation, loose/eroded terminals, etc.

 

[huzyrdaddy]

Redid all battery connections. Clean. Solid. Cables look good. Turn key to power on and volt meter read 12v. Heating glow plug dropped a smidge. Turned over to start and everything went dark. No dash lights volt meter dropped to nothing. Turn key off. Turned key back to power and nothing.

 

[hosspuller]

Had a similar problem. Turned out to be the battery. A broken internal connection. It was enough to show 12 volts on the meter but not enough material to carry starting current... until eventually it burned through.

 

[Ronsii]

Make sure you check both ends of the battery cables, sounds like maybe the ground cable to the frame... or on the solenoid end of the positive cable. usually it is best to take them completely apart and wire brush and crustyness/rustyness from them as you want nice clean bare metal showing for a good low resistance connection.

 

[Birken Vogt]

A problem like this you have to think like the electricity. Follow it out with the voltmeter one step at a time from whichever end makes the most sense.

I would start by measuring voltage at the starter solenoid battery hot to the starter case ground. It sounds like you already did this. What is the voltage there when trying to crank. Then check what the starter solenoid switch terminal is getting reference to the starter case ground. Is this also close to 12V when trying to crank or is it a lot less? Follow it back until you have good voltage. Or check what battery terminal voltage is doing when all this happens.

Usually good voltage followed by failure to crank and everything going dark will be a rusted up connection where one little blip is all the contact it is making and the starter burns that away leaving nothing. When it is still dark leave the key and everything on (lights etc.) and you will see +12v on the good side of the terminal and next to nothing on the downstream side. Check voltage from both sides of each suspect terminal and from the battery post to the clamp and from the clamp to the cable itself. Voltage across any of these should be near zero, should be the same piece of metal. At the bad one you will find 6-12V from one side to the other. Lots of ways to skin this cat.

 

[Wytruckwrench]

Look for no more that 1/2 volt drop anyplace in the system, when cranking. 13 volts at batteries and 12 at starter is already a 1 volt drop. Too much for the battery cables and ends. Start there cleaning everything and continue.

 

[Cat_man320]

If you have cleaned all the connection between battery, ignition and the starter and it still won't turn , the terminals or the connectors on the ends are not the problem . I suspect your trouble is in where the wire cable is connected to the terminals . Everything looks ok but the wire cable is not making the connection inside the terminal . It might show 12V on the meter but that means nothing, it's not voltage that turns the starter , it's amperage . you might have one strand of wire still connected showing 12 v but that single strand can't carry enough current to light a pen light . Prove to yourself that the starter is good and the engine can turn by using a set of jumper cables and give it a boost right at the starter with a known full charged battery , ground to ground and the hot to the large bolt on the starter , then just jump the solenoid with a screw driver . if it turns , well start replacing a cable one at a time until you find the open cable . MAKE SURE WHEN BOOSTING THAT MACHING IS IN NEUTRAL AND HAND BRAKE IS ON !!!!

 

[Delmer]

It might show 12V on the meter but that means nothing, it's not voltage that turns the starter , it's amperage . you might have one strand of wire still connected showing 12 v but that single strand can't carry enough current to light a pen light .

I disagree, you NEED to test this under load. Either when the lights and everything have shut off with the key on, or when the starter is activated but you get nothing. There WON'T be 12 V because if the voltage is there then the amperage will flow.

Like Birken said, if the suspected connection you're testing has 12V across it, then the amperage is not flowing.

 

[Cat_man320]

Delmer, to say you disagree , what you are saying don't make sense. Just do reverse thinking for a minute , if he got amperage to turn the starter obviously he got 12v from a good solid source . But you can have 12v and not enough amperage to even engage the solenoid. like I said to even turn on a pen light . Those statements you have to agree with. I suspect, under load he has a connection or terminal that goes open under load or draw. I have no idea why he got 12v at one point and 6 v somewhere else without some serious testing and investigation, But you do agree that he can have 12v and little amperage .

 

[Birken Vogt]

You can have 12v at the starter through a whisker of wire but as soon as you hit the solenoid that 12v will become 0v. Then under that condition you need to back track the wiring and see where the voltage drop is occurring.

 

[Vetech63]

Like Ive seen someone else say in here many times...……………...buy a new machine.

 

[heymccall]

Dumb question, but are both battery positive cables connected?

 

[Cat_man320]

You can have 12v at the starter through a whisker of wire but as soon as you hit the solenoid that 12v will become 0v. Then under that condition you need to back track the wiring and see where the voltage drop is occurring.

Exactly what I said Birken .

 

[huzyrdaddy]

thank you all for your thoughts and knowledge. it turned out to be a corroded connection at the starter. without your guidance i would have put in a new alternator!