Good troubleshooting takes time. Everyone seems to be looking for
the magic tip that says replace this $13 part and your problems are
cured. You don't have to think, dig or diagnose, just buy the part and
install it. Unfortunately, it doesn’t work that way 99% of the time.
Thinking is hard work and educated thinking requires much more
effort than simple parts swapping. The complexity and age of these
5.0 Mustangs works against that, as well as the number of hands
that have “modified” the original design. Sometimes that
modification is well done with good workmanship and other times it
is mechanical road kill. It is very easy to become the victim of the
previous owner’s efforts.
I spend a great deal of time trying to communicate the methodology
of structured troubleshooting principles. For those who haven’t been
beaten with this stick before, here they are again:
1.) Understand the system. That involves reading some books to get
an overall picture of how it works. For 5.0 Mustangs, that list starts
with the Chilton shop manual and the Probst book, Ford Fuel
Injection & Electronic Engine Control 1988-1993 by Charles
Probst :ISBN 0-8376-0301-3. It's about $30 from Borders.com, see
http://www.amazon.com. Select books and then select
search. Use the ISBN number (without dashes or spaces) to do a
search. Use the ISBN number and your local library can get you a
loaner copy for free for 2 weeks or so. Another resource is the
following website by Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring:
http://www.veryuseful.com/mustang/tech/engine. Study
the diagrams and tech articles. There is an amazing amount of good
stuff in one place for FREE.
2.) Isolate the problem. You need to be able to break the system
down into functional blocks or subsystems. Once you know what
subsystem has failed, it is much easier to troubleshoot. Group
problem symptoms according to what system controls them. Don’t
look for a fix for ignition problems by adjusting the fuel pressure.
Have an organized, step by step, approach to work your way through
a subsystem and check its functions. Work all the way through a
subsystem before you quit and go off wildly chasing rabbits. You
have three tools to use in your efforts:
measure, meter and
observe. Use these three tools to narrow down the list of possible
failure points into a small, easily managed list of items.
3.) Install the fix. .Now that you have a short list of suspected
villains, plan your repair efforts so that you do the easy things first.
If an item from the easy list didn’t fix your problem, then look at the
high failure rate items. Spend some time here on Stangnet and you’ll
get an idea of what the most commonly replaced parts are, things
like TFI modules, ignition switches and fuel pumps.
If you make a change and it doesn’t relieve the problem symptoms,
put it back the way it was. I have a stack of parts from where I
swapped a part and it didn’t fix the problem. I put the old part back
on the car and the new part went on the shelf. Someday I will either
use them or trade them for something else.
Having said that, a repeat of my previous comments is in order:
See "Help me create the Surging Idle Checklist" at
http://forums.stangnet.com/showthread.php?t=534062
for help with your idle problems. The first post contains all the updates to the fixes. I continue to update it as more people post fixes or ask questions.
I'm not sure if it works for other people, but that crystal ball in my avatar is for decoration only.
