First Question:
How would I have
approached diagnosing this vehicle if I had it from the start?
Disclaimer: This is not necessarily the best
method or certainly not the only method.
My methods also change depending on the weather, lunch, etc... etc...
Many technicians are looking for
bullet proof step by step diagnostic approaches to the many problems we come
across. While there are many healthy habits and processes we should all use, I
find it is more important to learn to be flexible and be able to use whatever
data is easily accessible first in an effort to narrow the possibilities
quickly. Many times there are so many possible causes to the problem being
analyzed, that there is no one size fits all diagnostic approach. I would
encourage all to jump right in with what is easiest and quickest and then think
your way in the right direction. As one gains experience with certain makes and
models, this gets easier and easier. With that in mind, read the following
answer to this question as but only one way to reach the diagnostic
conclusion.....
Probably the very first place to
start on a "crank-no-start" with this vehicle is to verify we have an
illuminated Service Engine Soon lamp on key-up. That will save you a lot of grief
at times.... The SES lamp was illuminated on this vehicle upon key-up. That
tells me that the ECM is most likely powered up properly. I am making an
assumption here, but I think it makes more sense to move on for now since the
idea is to zero in on the problem quickly. My next step(s) would be to verify spark and fuel pressure.
Which one I check first would be dependant on which one was easier to check. I
prefer not to handle fuel unless I have to, so I would have checked for spark
first. The ignition coils are on top and easy to get to. This would have left
me with the discovery that I had no spark at the coils. Now I have another
choice to make.... What to check next... For good spark we need good coils and
proper saturation and triggering of the primary. Lots of possibilities, right?
I would have started with checking
for good signals from the 18x and
3x Sync CKP sensors. This would have disclosed that both signals were 0v. I'm
sure they are out there, but I've never seen a hall-effect switch fail by
holding the reference signal low. At that point I would have checked the ICM
power and ground, which would have led me to the blown fuse. From here I would
have made a mental note of which circuits the fuse fed and then popped in a new
one and cranked the engine over. The engine would not have started and the fuse
would not have blown. From there I would have verified spark (which is now ok)
and then checked for fuel pressure with a gauge since the service port is right
up top and easy to get to.
From here I would have found power and ground to the fuel pump but the
pump would not be running. Keep in mind here, that upon key-up the ECM will
energize the fuel pump relay for two seconds and then wait for valid tach
pulses (engine running) before it keeps it energized. The fuel pump also is fed
B+ through the oil pressure switch, but you must have good oil pressure which
you will normally not have unless
the engine is running.
So now it would have all made sense. The
fuel pump locked up (becoming increasingly common out here), the amp draw went
sky-high, and the fuse blew... Now if the fuel pressure had been checked first,
it would have been a quicker diagnosis. Hindsight is 20:20, sometimes you lose,
and sometimes you win <g>