2012 f-250 6.7 , starter was turning over slow, talked to my mechanic friends they said the batterys were probply bad, replaced both batterys , starter still slow , i thought starter was bad, replaced starter, turn key , one click, maybe bad starter, removed new starter had it checked , said it was fine, re installed it , started right up. started 4 times in a row, 5th time wont turn over , just one click. checked fuse and relay , both good, any ideas?

 

Any CELs, codes or lights on dash? The first thing that comes to mind is the main harness that cuts across the front of the engine on the front frame cross member in front of the engine. I've read here that there is a small wire that corrodes and causes alternator problems and a battery light to come on the dash. Not sure if this would effect the start of the engine or be a place to start looking.

 

not throwing any codes, checked it running and stopped, no battery light,

 

Double check all your cables for clean and solid connections (at the batteries, where they terminate). It could be a potential grounding issue, so eliminate that possibility next. If all that checks out it might just be a starter that has some bad windings in it or a flaky solenoid.

 

i cleaned battery cables connections and starter connectors, loosened and retightened on ground i thought was starter cable ground. bad starter drawing to many amp , partialy melted starter wire ?

 

So, you're stating that you have a partially melted starter cable? If so, then yeah, that starter sounds like it's the issue.

 

sorry, i dont have a partialy melted cable, just wondering if a bad starter would draw enough amps to do that or would blow the fuse

 

If the starter was drawing too many amps and the fuse didn't blow then yes, the cable's insulation could melt.

Get a multimeter on the connections/cables at the starter and test for voltage at rest, voltage under load, amperage under load. You'll need a clamp-on multimeter to get the amps.

My guess is that somewhere there is a poor connection.

 

thanks, i was a sonar technician in the navy, worked for a electrical co in montana , ill check that tomarrow, raining now here in west virginia,

 

There was a guy that had a 2017+ truck with batteries that leaked. There was corrosion on the battery cable lug that got into the cable itself and then electrical problems started. The entire cable had to be replaced.

 

Try removing the serpentine belt and see how it cranks then. My son replaced the battery, starter and cables on my ‘00 V-10 when I was out of the country and told me the engine was locked up. I got home to find the a/c clutch bearing had gone out and locked things up via the drive belt.

We’re both better now at diagnosing before replacing parts.

 

had a similar situation on one of my '97 powerstrokes except it was an alternator bearing that came apart and locked the alternator. the truck wouldn't start with the belt on.

 

starter still not working, tested voltage at starter, 12.2 on big bolt, 9 volt on small bolt on starter,
help

 

9v at the control side of starter solenoid is a voltage drop on that circuit.
A wiring diagram is needed to diag the circuit, should be 12v at that connection.
find the relay that controls that and look for problems supplying current to that connection on starter solenoid.
Start testing & stop with loading the parts cannon, till you can confirm problem.

 

can i check continunity from the relay connection to the starter, and can relays partially work , bad connection, or do they work or not work