So I have been trying to do more research on my no start/pcm issue. I had the pcm replaced due to no starts and anti-theft light bliinking. Dealer diagnosed it and got new keys. 6 days after I got the truck back, happened again. Triple A guy was able to cycle the key several times and got it started. So it seems there is an antenna in the ignition switch collar itself. Could that be intermittently frizzing out causing my no start? Has anyone replaced one before? If I find out this is my problem and not a $1600 pcm, I am gonna be pissed..

 

Jess, this is what happens when a problem is not proven by testing.
Does the Theift lamp flash?
If yes, it's a PATS issue.
The dash lamp will flash a code if so.
The code tell what the issue is.
Turn the ignition to run and let it set for about 3 minutes.
From there it is persued per the code discription.
Replacing a PCM on a thought is very pi**ing indead.
Good luck.

 

Thanks Bluegrass. I just went to the store, truck sat overnight. First cycle, wouldn't start, theft light was flashing. I turned the key back to "off", cycled it again and it fired right up. The saga continues...

 

my 2000 is doing the same thing if I cycle the key a few times and listen for the pump to cycle it will fire up fine. i changes keys also after reading several things on this board and couple other ones. it didnt help. Makes me wonder of the linkage is getting worn enough not to trigger every time.

 

To make something clear, the fuel pump start at key on, has no relationship to the PATS.
PATS is the control signal through a dedicated buss path to the PCM, for ignition.
If it does not see the PATS signal, the ignition is inhibited.
.
The way the pump starts for a second is purely the igniton switch powers the PCM on.
A circuit in the PCM with a short timer grounds the pump relay circuit pulling up the relay and transfering power to the pump.
When the timer runs out, the ground to the relay is opened and the pump stops.
Upon cranking, the crank sensor sends it's signal to the PCM causing the same timer circuit to reground the pump relay full time as long as the crank is turning.
I can't stress enough these systems are quite involved in design and application.
A fault anywhere in the system depending on how it acts will cause the issue.

 

Thanks Bluegrass! Excelent description. You seem to know way more than the average joe about these systems. Are you a Ford tech or did you have a similar problem that you chased into the ground?

 

Hey Bluegrass this is my first time on this site but it looks very helpfull. My 99 f150 will not start. My mechanic replaced the Neutral Safety Switch he calls it. The truck is still not starting, any ideas on where I can began to check? any info is very helpfull.
[*]

 

From what there is so far, the PCM has been eliminated as a very expensive guess.
If you see the theft lamp flash there is something going on with the PATS system.
Turn the key to run. If the lamp flashes let it set for as long as 3 minutes and watch for a two digit code to be flashed.
You must begin with some evidence to persue the cause.