99 Ford 150 expedition intermittent won't start

Asked by Jun 07, 2017 at 01:40 AM about the 1999 Ford Expedition 4 Dr Eddie Bauer SUV

Question type: Maintenance & Repair

Expy failed going up hill on short out of town
trip.   replaced fuel filter that was clogged..
ran perfect for 3 days. It failed after errands
in a parking lot.. went to get it.. i drove it
home.. for 2 days cranked perfect..
continued to run gas out over the next few
days  so the fuel pump would be easier to
change.  It failed to start again for five days.
Researched . I have Chilton's ECT. There is a
limited amount  of info in them. I am an ex
electronic tech.  Understand relays ECT.   So
watched videos ECT.  Checked Schrader
valve had gas there. I decided to turn the
engine over.. it started (we are dealing with
an intermittent here) I took it to a neighbor  
and he put a bid tool on it.. not a cheap one..
it initially said misfire on cylinder 4.. that
made sense because when it quit, it did
misfire going up hills   I told him  to clear the
memory.. He found no codes..no cam
sensor problems, no crankshaft sensor
problems, always has had the sound of
prime, never checked voltage at  fuel pump
relay or pump itself.  I hesitate to pup 12
volts to fuel pump willy nilly, as it may feed
back and destroy electronic infrastructure.   I
know this can be the inertia switch (they
sometimes are intermittent). It could be an
insulation leak to the chassis.  I don't know if
I am getting spark.. it seems like like the obd
tester would catch that.. The problem is that
it is intermittent. I notice this doesn't have
the normal spark plug wire setup  and I think
this  is cop setup.  I am a little  confused
how to properly check for spark do I use a
noid.  Oh yes it is only showing about 30 psi
on idle and 35 on acceleration maybe a little
higher at high rpms.  Also my  fuse board
under the hood and  below the steering
wheel does allow pull and replace of relays.  
If it comes down to it I can fix boards, but if
it's a expensive chip.. that probably won't be
happening.. I suspect we are dealing with an
obvious component. If  any body can give
me a detailed  description of how this all
works please do so.

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