Magnum Maladies


A friend of mine has a ’93 W150, 5.2L. A
month ago, it wouldn’t start.
He installed a new cap, rotor,
wires, plugs, and it started. But
it had a miss, ran rough, rich
etc. He replaced the O2 sensor,
throttle sensor, you name it—he
replaced it, including putting
on a scope and finding one
bad injector. But this did not
solve the problem. I told him he
should rock the crank back and
forth to check for loose timing
chain (170k mi.) crank to cam
position sensors. But he didn’t
buy my thinking.
In frustration he turned the
distributor (don’t know which
way) and this solved the problem
completely, he got good
mileage back etc. Here’s my
question: could he be fooling
the PCM by changing the
cam position sensor to correct
for chain stretch? Could he
have gotten a cap that wasn’t
indexed right? My last question
is, if you’ve had the distributor
out of these Magnum engines,
what is the procedure for
indexing it so the cam position
sensor is correct? The Chilton’s
book I have says to put #1 at
TDC and align rotor to #1 on
the cap. This seems too simple
to me. I know if anyone can
clear this up you can.

I think you’re basically on
the right track. I don’t think it
is fooling the engine controller,
however, as the distributor
pickup only controls injector
timing, which is not critical at
all. I think the chain stretched

so much that the rotor was
mis‑phased to the cap and
couldn’t fire the plug(s). The
sharp edges of the new cap’s
tower terminals allowed it to
start, since sparks jump easier
to clean, sharp edges, pointed
objects, etc.
The distributor is phased
this way:

  1. Crank at #1 TDC (compression
  2. Rotate distributor so
    rotor is directly pointing at the
    notch in the pickup plate—it
    should say “cyl #1” right near
    the notch. This is a few degrees
    CCW (viewed from the top)
    from the rectangular cap‑locating
  3. Tighten the clamp, reinstall
    the cap. Done.

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