91 f-250 7.3 IDI fast crank with new starter and batteries goes to extremely slow
 

Well guys, I've owned her for about a year now. Love the truck, seems like one thing after another though. So anyway, I'll attempt to make a long story less long. truck sat most winter due to bad block heater plug in, put that in a few days ago. Never did test it until today. Also has brand new starter, had old one tested and it was bad, also new batteries (850cca) it was a cold 30 degrees yesterday in PA and couldn't get the truck to fire up. It's a hard HARD cold start. (Fires up first or second twist of the key in 70 degrees +.) So I killed the batteries, took them to get charged. Didn't even put them in until today. I turned the key one time this morning. Didn't want to risk killing the batteries so I decided I'd plug it in for awhile. I left it plugged in for 45 minutes and I felt around the block plug to see if it was warm, it was. So I unplugged my extension cord. And went to start the truck. The motor turns fast and fine, like normal, fired almost right up but died out. So I shut the key off and go to turn it again. It turned extremely slow! It turned so slow it was like completely dead batteries. so far I have checked batteries both reading 12.3 with multimeter/ test light. Have tried to jump the starter, still turns slow. I cleaned all battery terminals and leads. I looked at both of the grounds from the negative leads from the batteries. They both ground into the front end of the block, however that's where I stopped because I ran out of daylight! Please any info or ideas would be greatly appreciated. I am fairly new to diesel. So I'm not sure what could have caused this!
Thanks in advance.
Nick

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Forgot to add that the grounds to the block from the neg battery terminals both looked good and soild from a wiggle test, I'm off tomorrow so first thing I'm going to do is pick up there where I left off.

Bet you that positive cable is toasted, I would replace it just as a preventative maintenance. Go as thick as you can get it.

Thank you dortiz! Your input is greatly appreciated. Is there any way to know for sure that it's shot? I am going to mess with the grounds this afternoon, and if that's not it. Then I'll be replacing the positive cable. Thanks again.

Could check it for resistance, or cut open the heat shrinking to check the condition of the wire, but you would need to replace it after that lol

I've tested the positive cable from the end of the ignition (at the battery) all the way to the starter. With a multi meter. Getting all solid reads of 12.0-12.3. Messed with and cleaned up all the grounds. Still nothing. Don't have a clue. The positive terminal post on the starter is getting 12.0, also tested the positive cable between batteries. Reading a 12.3.

Could pull the starter, and have it tested, maybe it was a dud

The starter is 2 weeks old, it is "remanufactured" but after it started to turn over slow. that was my first guess. I pulled it and took it to napa an had them test it, it is good.

I would have my batteries load tested, even if they are newer, anything and everything can be defective.

The starter is 2 weeks old, it is "remanufactured" but after it started to turn over slow. that was my first guess. I pulled it and took it to napa an had them test it, it is good.

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Whoops, sorry about the last post, my phone is screwy. That sounds like a plan. Going to do that now.

I would replace the positive cable .... Reason ... It may get good voltage .... Do an ohms test with the cables .... Make sure there not attached to the engine or batteries... This is more conclusive evidence as to what the actual condition of the cables is in ..... 2guage or bigger Should be around 1ohm at most....

keep us posted..:c: