4.0 won't turn over after running

[Dufussman]

Hi guys I'm new here. Yes I tried to search the answer but this is a massive forum.
My 06 4.0 auto has developed the problem in title. Cold starts normally, runs normally no idle or power issues. Will restart at lower engine temps but on a longish drive when engine reaches its peak temp it will not restart nor turn over until cooled. I'm on my 3rd starter so I don't think thats it especially since it starts after cooling and I put a high quality one in last time. No check engine lights, and really no other symptoms maybe a very quiet muffled whoosh of air when I shut it off that seems new. Brand new battery, new fuel pump. Can still use the truck but need help. Many thanks!

 

[RonD]

Welcome to TRS

It is an odd symptom
No crank when engine bay is warm

Starter motors need 60-75amps to turn engine over, which is why the battery cables to starter and engine ground are so big, that's alot of AMPs

Yes, starter motor would have been my first guess
Next guess would be battery cables, both Positive and Negative cables need to be able to pass the same AMPs or neither can
As the temperature of a wire goes up so does its Resistance to pass amps, this is why a wire can get hot and melt when there is a short, internal heat of course but same high resistance when full amps are passed thru it, lol
So when engine bay is hot so are both positive and negative cables

You could disable coil pack so no start when cold
Then crank engine over a few times for 10 seconds or so each time
Then feel each positive and negative cable for HOT spots were higher amps are being blocked
Replace that cable

 

[Dufussman]

Interesting Ron thanks. I was thinking a sensor or something but that could be it. I'll start with the grounds. I know theres one right beside the battery. Know any other spots? Would I get the same "hot' spot on wires if engine was running?

 

[RonD]

The larger negative cable runs to engine or bell housing by starter, that's the Ground cable that needs to be good for starter motor
As is the larger positive cable

The smaller negative(or positive) wires are for the lights, relays, ect................
But smaller wires could cause issue with Starter Relay in fuse box

The 2006 Ranger will also have PATS(passive anti-theft system), its not an alarm, just disables starter motor and fuel injectors if correct key is not seen in ignition with Key On, i.e. uses transponder keys

But...............there would be a flashing THEFT light(padlock) on the dash if PATS was activated, which you didn't mention
And it would be hard for this system to be heat sensitive

 

[Dufussman]

So here’s an update. Problem still exists after addressing grounds and cleaning/sanding their contact points.

I decided that instead of replacing the grounds I have I’d simply add more as an upgrade. Added a 4 gauge from neg battery terminal directly to mounting bolt for pre existing ground on starter. Added another ground from battery to ground near radiator. Will be adding another 4 gauge ground from engine to firewall tomorrow but I don’t think that has anything to do with my issue.

Any more ideas? Lots of things might cause crank with no start but this is weird. Maybe starter power wires, vapor lock, I dunno.

 

[rumblecloud]

Even with no CEL, I'd still look for codes.
But it is strange.

Oh, Welcome to TRS.

 

[Uncle Gump]

I would think some voltage drop testing would be in order.

perform voltage drop testing on the high current starter circuits when cold... then do it again hot when the problem exists. If you don't find the high resistance... at least you can rule the cables out going forward.

 

[Dufussman]

Hey guys I'm narrowing down the issue and getting more ticked in the process. Finished all grounds and had my mechanic at work do a brief inspection, check for codes, and rule out the starter. He did rule out the starter, no codes, and the next go will start checking what wire, harness, and/or part is the culprit.

Meantime, any further ideas? I've read about the ignition switch (rectangular white thing near the steering column) sometimes have issues with no start/crank. Don't know after that. Also, I'll start trying to look into wire harnesses and clean them etc but I haven't spotted any large ones. Does anyone know where the major junction points are?