Have a 2007 Pacifica with 4.0 (bought it new). For the past year or two it is sometimes very slow to start. Starter will spin the engine over properly (at correct speed), nothing sluggish. It doesn't spit or sputter, just takes several seconds to even think about cranking up. I don't think it does it when the engine is cold. Every time I have noticed it is when the engine was hot/warm and you park it for a few minutes (even as much as 30 minutes). I have talked to 4 or 5 mechanics/shops and none will stick their neck out. I suspected fuel pressure/pump so one shop tried it for a few days and only got it slow start once. I had them go ahead an put in a new pump anyway. Didn't solve the problem. Had them change the plugs as well--they needed it with 160K miles on them. Still have the same problem. Pretty sure they reset the computer as well. Any ideas?

 

How old is the battery?
An old weak battery can cause those kinds of issues, since so many components in the car are controlled by computers that require the correct amount of power to do their job.

Also, when the starter has been heated up, it can require more power to crank over the engine, due to increased resistance of heated components.
That could also indicate a failing starter that is dragging and drawing more power.

 

Battery seems fine, been acting this way for a couple years so I would think a bad battery issue would have come to a head by now. Have never noticed a decrease in the RPM's the starter turns the battery over.
For a few years the car had another really weird issue. You would turn the key and the starter would not do anything, it would not click, grind, groan, NOTHING. Finally the darn thing would spin and crank. It hasn't done that crazy stunt in a LOOONG time. I did add an extra ground cable--think I ran it from the batter to a starter mounting bolt.

Wonder if the computer is faulty? I had a 91 Ford truck do things that made no sense changed the computer and problem solved.

 

That is possible. The computer controls everything, including telling the starter when to crank over the engine.

 

Computers rarely fail. Sensors however do age and can be affected by temperature. Crankshaft position sensor senses rotation, cam sensor location of #1. If either of these signals is weak but not quite out of spec no code will be reported but could have an impact on starting. Heat affects resistance and could be a factor. Signals can be checked with a scope if available. If you do change the sensors, use OEM not aftermarket. Have not had good luck with aftermarket sensors.
Timing belt been replaced? 7 year/100k interval and if stretched could throw the timing off just enough to hard start.

 

Timing belt was replaced about 50K ago. So how hard is it to change those 2 sensors? Any special tools required?

 

It should be a 10mm wrench and a couple of minutes each.
The crankshaft sensor is on the back side of the engine, camshaft sensor on the top front of the engine.

 

Anything that requires reprograming or is this just bolt in the new ones?