intermittent starting issues

Had a 2013 Western Star do this. Changed the whole starter and it went away

 

Please post VIN and engine type.

This sounds like an extended crank issue, correct? It does always crank and not start, right?

I would be troubleshooting the fuel system. Have you monitored pressure with scan tool while cranking or installed a mechanical gauge? This is where I would begin.

 

If it’s not cranking all, it sounds like a 39MT Delco starter. In my experience the brushes are sticking in it. More than likely the nose housing has let the planetary gear outer ring wear down into the housing. Depending on how cheap you want to work, you could probably replace the nose housing and the brushes and have it good as new for @ $100 in parts and 30-60 min of labor.

You might be able to confirm this by setting the conditions where is would mess up and smack the bottom of the starter with a hammer. If it works without hesitation, this is more than likely the problem.

 

Modern Detroit's when you turn the key, the key switch sends a signal to the ECM that you want to start the truck. The ECM then sends a signal to the start relay when it figures all data indicated that it is safe to start.
Maybe the ECM is detecting a parameter that isn't ready for engine start up. Such as transmission in neutral.
Or a bad wire some where.

 

It probably never will fail on the bench, there's no load on it.

Check the ring gear for defects, make sure there's no messed up teeth on it and that it's round and straight.

If the engine is computer controlled there may be a timed protection circuit of some kind that calls for a rest period before trying again.

There might be a dead spot on the armature.

The solenoid might be weak.

You may have a bad ignition switch that's intermittent or has a quirk.

Check the battery terminals for carbon build up and carbon arcing.

Check the battery(s) to.
I've seen new batteries with loose plates that would short out intermittently and do similar to what you are describing.

Does it happen when the engine is hot and cold?

Just throwing some ideas at you.

 

You gotta break out the multi meter. Check if there's power even getting to the solenoid and check that there's power getting into the starter. No power? Keep working backwards until you find the power.

 

Yes, and if you are working alone you can prop up the multi meter and your cell phone to record the readings with the video camera.