I searched but I could not find anything quite on point, so I am asking. Forgive me if it has been discussed previously, I looked, I just could not find it!

Truck is a 1991 F-150 XLT lariat 4.9 l / 5 speed

This summer I went through a whole long ordeal of trouble shooting what ended up being a bad computer. Long story short

A shop replaced the MAP sensor, and the distributor
I ended up replacing the ECT sensor, TPS, IAC, TB gasket, cleaned the TB before I found bad caps in the computer. The truck would not run, it stumbled, bucked and stalled.

Any way

I noticed as the season changed to fall here in VA, that after driving the truck and getting it warmed up, it is hard to start. On a cold start, the starter sounds as expected, the engine turns over, and it starts right up. If I take it out for a 10-15 minute drive, and get it all warmed up, then stop, and start it up a few minutes later the sound can only be described as though the starter is struggling to turn the engine, as though the engine's rotation was being hindered somehow. if I stop trying to start it, tap the gas and try again, it still sounds as though it is struggling, but it catches and fires up.

The first time this happened a few weeks ago I thought it sounded like a weak battery. I checked voltage at the battery with the engine running at it was something like 14.1 volts, and with the engine off the battery was at 13 something.

Any thoughts, other trouble shooting steps?

Thanks

 

Check the starter. Connections, wire condition etc. If nothing external helps, pull the starter. You can very carefully pull the end cap and check the condition of the brushes.
A tired starter or one with poor connections has a harder time operating when it's hot.

 

I had exactly the same hot/warm start sluggishness. Fiddled with a few things, thought the clogged cat and old dirty assed 02 sensor might be causing it. Changed the exhaust out from manifold back and new sensor to no avail, but after changing the throttle pos sensor, problem is gone. Tried the same errand running where it would rear it's ugly head, but after a couple weeks, still no problem. ETA: I've got a 95 5.0. Here's what the wiring coming off of it looked like:

 

If you drop your starter, check all of the connections/wires to make sure they are cleanand unbroken. A bad connection will cause wierd problems like a bad ground. At the very least you could clean all of the connections and put dielectric grease on there to help prevent some corrosion in the near future. Be warned that a car wash can remove the grease. As Chris 1 said you can check the brushes if you're careful.

Another thing to think about is the oil. Have you changed it recently to another weight? Have you ever dropped the oil pan and seen sludge build up? All of these little things add up. The TPS wiring could have cracks in it that allowed dirt to enter. Could cause a faulty reading to the computer.

Just another thought, did they set your timing to factory specs? I know some people on here with the 4.9 adjusted the timing for better performance and gas mileage.

 

I finally had time to look at this again. I did find the negative battery cable was kinda loose, so I tightened it up properly. On a hot start the symptoms are greatly reduced, but it still feels like it is straining a bit for lack of a better term.

If I decide to hang on to this truck I will drop the starter. It has a few other issues which I do not know if I feel like dealing with.

 

Might want to just crawl under there and have a look at the connections. Cleaning them up can make a huge difference.

 

Check your temp sensor. Its reading cold and flooding the engine on warm start.