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Jim Grant's Tech Tips
96 Chevy Astro, Check Engine Light and Plugged Exhaust
Q:
My
'96 Chevy Astro with 109k does not have any power and the check engine
light is on all the time. If I leave the AC off I can go up to 50mph,
if it's on I can only go to 30mph. Also it has a hard time climbing hills,
the transmission slips and shifts erratically. I took it to the dealer
and he says he is seeing a misfire code and wants to do a major tune-up.
One month ago the car was in for a 60k mile service and nothing was wrong
then. I took it to another shop and he says it's the transmission and
won't even bother to tune it. I took it to a third shop and he saw the
same code plus another one, but says I need to replace the exhaust system
(Catalytic converter and muffler) first and then possibly do a tune-up.
He says the exhaust is clogged and that's why I am getting the misfire
code.
A:
The
answer is technician # 3, but I would ask him to prove it first. Proving
a restricted exhaust is relatively easy but very annoying. To prove a
restricted exhaust only requires unbolting the exhaust. We have a Plymouth
Breeze in the shop that was lacking power with a check engine light on.
The computer had 2 codes; misfire detected in cylinder #1 and the engine
operating at too low of a temperature. Initial inspection found the engine
to be in good condition, starting and running well. Out on the road it
was a different story; the Plymouth would be in the way of any kid on
a tricycle. The exhaust pipe was unbolted from the manifold and secured
for a second test drive. It was the Jekyl and Hyde syndrome, the Breeze
roared to life. The conclusion? The exhaust is restricted. Now many will
jump to the conclusion that the catalytic converter is plugged and they
are most likely right. But a word of warning, the inlet and outlet pipe
to the converter should be cut open to allow for inspection. Why? Many
exhaust systems use a dual walled pipe at the front of the system. We
have seen the inner wall of this pipe collapse and create the same condition
as a plugged converter. Have tech #3 unbolt the exhaust and test drive
the vehicle. If power returns, the exhaust is restricted and needs to
be inspected. If the converter is the cause then the cause for the converter's
failure must be found. In the case of the Breeze it's likely due to the
second computer code. The thermostat is opening too early, causing a lower
coolant temperature. When coolant temperature is low the computer adds
more fuel. Operating an engine under this condition for too long of a
period will cause converter melt down.
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