[Vwdiesel] OT: remote diagnosis

[Scott Kair]

    Sorry for the semi-OT, but the pool of expertise here is too
astute not to ask.
    My assigned plow truck is a 1990 IH/ Navstar with their DT 466
inline-6, converted from a garbage packer chassis to a dump truck.
Engine has been exhibiting a slight miss which becomes conspicuous
under load, i.e.- when fully loaded with material and applying power.
    We changed fuel filters, with only a slight improvement in overall
running.  One of our mechanics mentioned that he had a IR thermometer
with a laser sensor, so we took a reading of the exhaust manifolds at
the head, on the five cylinders we could access with the hood lifted.
Engine was cold and idling.
    The IR thermometer was impressive.  On four of the cylinders, it
transmitted readings quickly enough to show a 40F +- fluctuation which
we assumed to be a temp fluctuation between strokes of the engine
cycle.  On four cylinders, the reading was between 190 and 230F at as
close to the head as I could shine the beam.  On one cylinder, the
reading was a fairly constant 120F.
    I can't vouch for the accuracy of the thermometer, but what was
striking was the differential between the 4 fairly constant cylinders
and the one that was conspicuously and constantly low.  It seemed
fairly apparent to me that a good starting point would be to examine
seriously the injector in the low-temp cylinder.  Unfortunately, shop
management claims that the problem is faulty fuel- a known issue.
Their non-solution is to drive it until it quits running, and then to
replace the entire aged unit. I disagree, but before I go over their
heads, I'd appreciate some opinions from the group.
    TIA,
    Scott Kair