Any ideas, recently my IROC devoloped what
I thought was a knocking sound in the
upper engine, (87 305 TPI auto)but the
sound was not like metal to metal it was
sort of a dull almost thud but would
increase with rpm, I would not hear it at
idle or 2200 rpm, 70 mph, I would hear it
mostly taking off from a stop and would
increase then when up to freeway speed I
could not hear it anymore, performance has
not suffered at all and oil pressure is
the same and temp is normal. Then this
morning I started it up and the exhaust
gases where really bad, burning eyes and
throat, never had that problem before,
never failed smog. After looking around
somemore I think it may have something to
do with the air injection reactor (A.I.R.)
system. The pump itself seems to be
working and the noise seems to be coming
from the rear center, pass side of engine,
and as I squeezed one of the hoses from
the pump the air pulse seemed to match
the noise, then I removed the belt from
the pump but the noise was still there, so
that stumped me, but the fumes are bad, no
visable smoke either, and removing the
system is unfortunatly not an option here
in Vegas.
Anyone know much about these systems, I am
open to ideas and suggestions, and again
no it can not be removed.

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TPIS airfoil,relocated MAT,AFPR,TB h2o bypass
March Underdrive Pulleys
otherwise stock 5.0TPI
700r4, 10 bolt 3.23 g92 axle, 4 wh. disc brks.

 

87,

There are check valves in the A.I.R. system that are supposed to divert exhaust pulses from the pump and allow air to flow to the exhaust manifolds (one direction only). These valves are located at each side of the engine, and are not impervious to failure. I've replaced several over the years on several of my engines due to failures.

This one is identified:




This one is right of the AC accumulator:



The pulsations you feel in the hose from the A.I.R. pump could be failed check valves allowing exhaust pulses to return to the pump, which may also cause the noise you are hearing.

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Later,
Vader
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Justice and Freedom will Prevail
Adobe Acrobat Reader

 

I'd maybe think of pulling a valvecover and checking springs and rockers if it's a mechanical noise.