[Shotimes] What can destroy a cat?

[Paul Nimz]

You can get a small in line needle valve.  Unless you have non stock cams I
think the vacuum gage will show if the valve guides are worn , a 3-4"
oscillation is not common.

I currently have a temporary gage set up in my '97.

Paul Nimz
'97 TR
'93 EG mtx


----- Original Message ----- 
From: "Kevin & Cheryl Airth" <clubairth@peoplepc.com>
To: "Paul Nimz" <pnimz@v8sho.com>; <cmichaelo@optonline.net>
Cc: "shotimes" <shotimes@autox.team.net>
Sent: Saturday, June 19, 2004 12:12 PM
Subject: Re: RE: [Shotimes] What can destroy a cat?


> Thanks Paul!!
> I had forgot about using a vacuum gauge. Here is why. Have you attempted
> this? I have found the vacuum gauge and it's actions are so wide open to
> interpretation that everyone who looked at the readings came up with a
> different answer!! I think vacuum tests would be more useful if we could
> some how get a baseline for each engine. Maybe with 2 SHO's side by side
and
> using the same gauge and the same tests. That might give you a leg up on
> what is actually happening inside the engine. You do mention something
that
> may have messed up my experiences. My vacuum gauge does NOT have the gauge
> damper control. I have not seen one with it? Maybe my gauge is a cheap one
> but the damper adjustment would put another variable in the system that
has
> too many already?
> .
> .
>
>
>
> > You can use a vacuum gage to help with the diagnostics.
> >
> >
> > Intake Manifold Vacuum Test
> >
> > Bring the engine to normal operating temperature. Connect Rotunda
> > Vacuum/Pressure Tester 164-R0253 or equivalent to the intake manifold
> > (9424). Run the engine at the specified idle speed.
> >
> > The vacuum gauge should read between 51-74 kPa (15-22 in-Hg) depending
> upon
> > the engine condition and the altitude at which the test is performed.
> > SUBTRACT 4.0193 kPa (1 in-Hg) FROM THE SPECIFIED READING FOR EVERY 304.8
m
> > (1,000 FEET) OF ELEVATION ABOVE SEA LEVEL.
> >
> > The reading should be quite steady. If necessary, adjust the gauge
damper
> > control (where used) if the needle is fluttering rapidly. Adjust damper
> > until needle moves easily without excessive flutter.
> >
> >
> > Vacuum Gauge Readings--Interpretation
> >
> > A careful study of the vacuum gauge reading while the engine is idling
> will
> > help pinpoint trouble areas. Always conduct other appropriate tests
before
> > arriving at a final diagnostic decision. Vacuum gauge readings, although
> > helpful, must be interpreted carefully.
> >
> > Most vacuum gauges have a NORMAL band indicated on the gauge face.
> >
> >
> >
> > Following are potential gauge readings. Some are normal; others should
be
> > investigated further.
> >
> >
> >
> > 1. NORMAL READING: Needle between 51-74 kPa (15-22 in-Hg) and holding
> > steady.
> >
> > 2. NORMAL READING DURING RAPID ACCELERATION AND DECELERATION: When
engine
> is
> > rapidly accelerated (dotted needle), needle will drop to a low (not to
> zero)
> > reading. When throttle is suddenly released, the needle will snap back
up
> to
> > a higher than normal figure.
> >
> > 3. NORMAL FOR HIGH-LIFT CAMSHAFT WITH LARGE OVERLAP: Needle will
register
> as
> > low as 51 kPa (15 in-Hg) but will be relatively steady. Some oscillation
> is
> > normal.
> >
> > 4. WORN RINGS OR DILUTED OIL: When engine is accelerated (dotted
needle),
> > needle drops to 0 kPa (0 in-Hg). Upon deceleration, needle runs slightly
> > above 74 kPa (22 in-Hg).
> >
> > 5. STICKING VALVES: When the needle (dotted) remains steady at a normal
> > vacuum but occasionally flicks (sharp, fast movement) down and back
about
> 13
> > kPa (4 in-Hg), one or more valves may be sticking.
> >
> > 6. BURNED OR WARPED VALVES: A regular, evenly-spaced, downscale flicking
> of
> > the needle indicates one or more burned or warped valves. Insufficient
> > hydraulic valve tappet clearance will also cause this reaction.
> >
> > 7. POOR VALVE SEATING: A small but regular downscale flicking can mean
one
> > or more valves are not seating.
> >
> > 8. WORN VALVE GUIDES: When the needle oscillates (swings back and
forth),
> > over about a 13 kPa (4 in-Hg) range at idle speed, the valve guides
could
> be
> > worn. As engine speed increases, needle will become steady if guides are
> > responsible.
> >
> > 9. WEAK VALVE SPRINGS: When the needle oscillation becomes more violent
as
> > engine rpm is increased, weak valve springs (6513) are indicated. The
> > reading at idle could be relatively steady.
> >
> > 10. LATE VALVE TIMING: A steady but low reading could be caused by late
> > valve timing.
> >
> > 11. IGNITION TIMING RETARDING: Retarded ignition timing will produce a
> > steady but somewhat low reading.
> >
> > 12. INSUFFICIENT SPARK PLUG GAP: When plugs are gapped too close, a
> regular,
> > small pulsation of the needle can occur.
> >
> > 13. INTAKE LEAK: A low, steady reading which can be caused by an intake
> > manifold or throttle body mounting flange gasket leak.
> >
> > 14. BLOWN HEAD GASKET: A regular drop of fair magnitude can be caused by
a
> > blown head gasket (6051) or warped head-to-block surface.
> >
> > 15. RESTRICTED EXHAUST SYSTEM: When the engine is first started and is
> > idling, the reading may be normal but as the engine rpm is increased,
the
> > back pressure caused by a clogged muffler (5230), kinked tail pipe or
> other
> > concerns, will cause the needle to slowly drop to zero. The needle then
> may
> > slowly rise. Excessive exhaust clogging will cause the needle to drop to
a
> > low point even if the engine is only idling.
> >
> >  When vacuum leaks are indicated, pinpoint and correct the cause. Excess
> air
> > leaking into the system will upset the fuel mixture and cause concerns
> such
> > as rough idle, missing on acceleration or burned valves. If the leak
> exists
> > in the power brake, the system will not function correctly. ALWAYS FIX
> > VACUUM LEAKS.
> >
> >
> >
> > Paul Nimz
> > '97 TR
> > '93 EG mtx