Ford Repair: Ford F150 starting problem, amp load, resistance changes

Question
Two weeks ago my 1996 f150 4.9,mt, 4x4 seemed like it was starting to turn over slower.On the way to the shop I stopped and it would not start.(turned over very slowly). Waited 5 minutes it turned enough to start. Of course it started fine for them. The shop used a hand help unit and said my charging system was working okay. Recommended me to another place that specializes in electrical problems. Four days still later no signs of the problem. Stopped by the other place and they used several larger testing systems to check it.Again the charging system worked fine, but they felt the starter was putting a slight draw and was probably starting to go bad. So we put a starter on and two days later it happened again. While driving sometimes the charging gauge will vary, on the plus side of the middle reading and sometimes just below midpoint. Battery is 5 months old, all connections tight and clean. Any thoughts??  Thanks in advance. Sorry for the novel..

Answer
Hello Steve,
         The problem you are describing definitely sounds like a starter draw issue that is temperature related(the vehicle underhood temp.actually rises after it is parked for a little while). Just because the battery is fairly new, does'nt mean its good. On an approximate 300 amp. load test, the voltage should'nt drop below 10 volts.  A new starter is'nt necessarly good either, but more unlikey. What happens is the starter motor and solenoid windings get heated up by the exhaust etc. and the resistance changes, so the amperage draw changes. What high draw causes is the battery to drop voltage which is that "dragging" type slow crank experienced. Starter amperage draw on that truck when hot really should'nt exceed 300A also. You also could have a bad diode(it has three inside, and they can't be replaced). What that causes is the alt. does'nt charge quite well enough, even though it is raising the voltage slightly. Properly testing a starting /charging system takes a few years of experience. Another thing to keep in mind is that if the ignition timing is too far advanced, it can cause the same problem. If you have had some tune type work done, or the distributor has been out,the timing might not be set properly. Those are about the only things I can think of besides bad/corroded connections. Good luck and I hope this helps! Shaun.