Ferrari Mailing List: 308 QV emissions failure and possible misfire

[Alexander Ishii (alexishii]

Hi All,

So my 84 QV has been stubbornly failing emissions (in NJ), and after some
repeated assertions by my usual mechanic that "all seems to be well", I've
found myself having to try and figure out the problem myself.

At the moment, the car is not idling right in my mind (despite what my
mechanic says).  For one, the idle speeds "hunts" a bit; not enough to be
seen on the tach, but enough to be felt as a slight change in the vibration
frequency of the engine.  Second, every couple of seconds one gets a
just-audible muffled "pop" sound from the engine, accompanied by a slight
puff of extra exhaust out of the tail pipes (no sound out of the air intake
system).  Also, the car is running sort of on the hot side (coolant temp
"idles" at 195).

Plugs and wires were changed not long ago, but other than that, nothing much
has required much tinkering in many years.

The "pop" has me thinking than one-or-more of the cylinders is
intermittently misfiring and dumping some un-burnt fuel into the exhaust
manifold (where it is igniting and "popping").  Given the "every couple of
seconds" nature of the problem, however, I have little doubt that all the
sparks will look fine when I try the usual tests.  Anyone have any
suggestions for how I might try and zero-in on the faulty system (short of
swapping-out every part one-by-one until the issue goes away)?

Also, it has also occurred to me that the problem might be that the
injectors are not atomizing properly, and leading to an complete burn (in
turn leading to exhaust manifold ignition of the leftover fuel).  Has anyone
seen symptoms like the above be remedied with replacement of the injectors?

All thoughts/opinions/experiences would be appreciatively accepted.

    Cheers,
    Alex