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Re: smog test from hell

    The most probable cause of the heat radiating from the cat is unburned
fuel burning in the cat due to the misfiring cylinder. This can be
dangerous - I stopped a group of teenage girls driving a misfiring Chrysler
in one night Toronto many years ago after I noticed red hot sparks coming
out of the tailpipe and a glow under the car. The cat was so hot that molten
metal was splashing on the ground under the car after they stopped. "I did
notice the floor was getting awful hot" one of them said.
    Try a compression test and a leak-down test on the engine - this will
tell you if you have a problem with rings or valves on #2.  You might also
have a bad valve stem seal on this cylinder, allowing oil into the
combustion chamber and coking up the plug. You've already gone the
wires/cap/rotor route which was the appropriate first step.
    Running the engine on the rack shouldn't cause a problem if the oil
pressure is good, the car didn't overheat, and he didn't over-rev the


Fred Munro
'91 200q  281k km

----- Original Message -----
From: William P. Magliocco <wmagliocco@sprintmail.com>
To: <quattro@audifans.com>
Sent: Monday, October 11, 1999 2:48 AM
Subject: smog test from hell

> Last week I took my '86 5kT (MC engine) to have a smog test done at the
> local garage.
> The first time on the dyno it failed.  The mechanic attempted to get the
> car to pass by tweaking the timing, then playing with the CO mixture
> adjustment on the air flow plate in the CIS box.  Neither allowed the car
> to pass.
> While it was failing, the car passed the CO and HC portions of the test
> with room to spare, only failing the NOx part of the test by about 25%.
> The next day, a cat was installed, and the car passed.
> All well and good, but now the car has become a dog to drive.  At idle and
> to about 1500-2000 RPM one can feel the car missing on a cylinder and also
> some shudder due to the miss.  In the 2000-3500 RPM range it seems ok.  I
> just drove the car from Phila. to DC over the weekend and it wasn't too
> on the interstate.
> In addition, while stuck in traffic I feel a great amount of heat
> from the cat when I drive "cabbie style".  Engine temp seems ok at this
> The best clue that I have is that the #2 plug gets fouled with carbon.
> I've tried cleaning the plugs, swapping the plugs around and even the
> (keeping the timing sequence proper)...no help.
> A few notes:
> 1-the week before the smog test I ran a emissions system cleaner
> ("Guaranteed to Pass" from CRC) mixed in with the gas.
> 2-Installed NEW wires (Beru connectors), Bosch cap, Bosch rotor and Bosch
> W7TDC plugs.  Before, I had the "chain store" Bosch WR7DP platinum plugs
> the car, for over a year, with no ill effects.  I know many out there
> think well of those "chain store" platinums.
> 3-after the car started stumbling, my mechanic gave me an engine cleaner
> made for GM...I allowed the engine vacuum to suck the contents of the can
> into the intake and it was quite cloudy upon starting the car up.
> 4-The dirty #2 plug can be swapped with another plug...the new plug will
> then clean itself up in another cylinder and the replacement plug in the
> cylinder will then get the carbon crust.
> 5-the tech kept the car on the smog rack for about an hour when trying to
> make it pass...would the combination of extended low speed driving (15
> and/or racing the motor to "blow the junk out" cause a problem with the
> valves or rings?
> Any help is welcome.