Doesn't alway's start
 

I have a 2000 4.6 W/M50D. The other day it wouldn't start, just crank over. Well it finally did start and run like nothing was wrong. Then again a day later it wouldn't start so I let it sit till the next day and it still wouldn't start. Well I dislocated the battery for 30 min. and when I hooked it back up it started and seems to run fine. Anyone else ever had this problem? No mods to motor by the way. I am forced to drive my old 73 Chevy until I figure this out. How embarasing. Thanks for any info.

Very common causes;

Bad starter solenoid
Corroded Starter wires (Underneath the insulation)
Old battery

Less common causes;

PATs issue
Bad starter
Bad alternator

Get yourself a cheap remote start switch a big a$$ screwdriver and next time it won't start jump the two large posts on the starter solenoid (On the firewall) if it starts you have found your problem.

good luck and let us know.

Actually it cranks over fine it just doesn't "light". Today it started fine but it would be nice to find out why it didn't before. One thing I was thinking is maybe the alarm is malfunctioning by killing the ignition intermitantly. Sound possible?

The factory security system (PATS) disables the starter also. Unless you have an aftermarket alarm system (you didn't specify) then the issue is elsewhere.

Fuel, Spark, or Air: one is missing.

Check for air by pressing the throttle 1/4 way while trying to start. If that allows it to start, then focus on the IAC.

Spark : A timing light is a hand way of checking for spark on any engine that uses plug wires.

Fuel: Attach a pressure guage to the fuel rail to see if your pump is supplying fuel under pressure.

One of these will point you to the correct subsystem to focus on. Failure to identify where to look will usually result in wasted time and money along with increased frustration.

Steve

Might want to check the IAC(Idle Air Control) check the voltage & resistance....also there is a procedure to clean the carbon deposits off of it! I am having a similar problem.