Car fails smog at high rpm. Need advice.
Rajiv Baronia
I have recently bought an '87 Chevy Nova (clone of Toyota Corolla).
I had a major tune-up done after buying it; and it drives perfectly.
However, it failed smog due to excessive CO (carbon monoxide) emissions
while running at high rpm (2500). Here in Calif., the maximum allowed
CO content at high rpm is 1.2% , but the car is running at almost 4%;
and therefore it failed.
The interesting thing is that the emissions are well within the limits
while running at idle; and the problem occurs only at high rpm. This
high content of CO and other hydrocarbons would normally indicate that
the fuel-mixture is pretty ritch; and should be made leaner. However,
the mechanic says that any tune-up/adjustment of fuel mixture would
only impact the idle conditions; and since the car does not show any
signs of excessive emissions at idle; further tune-up would not do any
good. He suspects that perhaps the carburetor is bad and should be
replaced. This obviously means big bucks for him.
Other than replacing the entire carburetor, is there anything else that
could be checked/replaced in order to reduce the emissions at high rpm.
Any pointers/suggestions would be appreciated. Thanks in advance,
- Rajiv Baronia
bar...@otter.nas.nasa.gov
Don T. Borowski
:
: I have recently bought an '87 Chevy Nova (clone of Toyota Corolla).
: I had a major tune-up done after buying it; and it drives perfectly.
: However, it failed smog due to excessive CO (carbon monoxide) emissions
: while running at high rpm (2500). Here in Calif., the maximum allowed
: CO content at high rpm is 1.2% , but the car is running at almost 4%;
: and therefore it failed.
:
: The interesting thing is that the emissions are well within the limits
: while running at idle; and the problem occurs only at high rpm. This
: high content of CO and other hydrocarbons would normally indicate that
: the fuel-mixture is pretty ritch; and should be made leaner. However,
: the mechanic says that any tune-up/adjustment of fuel mixture would
: only impact the idle conditions; and since the car does not show any
: signs of excessive emissions at idle
mixture at idle. At higher RPM, you are depending on the the correct
jetting to get the mixture right. Also, the fuel level in the float
bowl needs to be set right. A fairly common problem is having the
float saturated with fuel. It then does not float as well, and the
fuel level in the float bowl comes up. This will cause a rich mixture,
and thus high CO. A standard carburator rebuild kit will include a
new float.
Marginal CO problems can sometimes be solved by adjusting the float
level so the fuel level in the float bowl is just a hair low, though
doing this too agressively can cause
fuel starvation during acceleration/deceleration/cornering.
Donald Borowski WA6OMI Hewlett-Packard, Spokane Division
"Angels are able to fly because they take themselves so lightly."
-G.K. Chesterton
pa...@emav151.rtp.dg.com
It could be the EGR valve. Exhaust gas recirculation valve. It's
mounted on the intake manifold and it reciculates exhaust gas back
into the intake manifold at higher rpm, it closes at idle. It may
be disconnected or stuck closed. Its round and about 2' in diameter
with a small suction hose going to the top of it. Sometimes you
can feel under it with your fingers and push up on it and feel it
move up and down. Also you can take it off ( two bolts) and
see if it's been blocked off and inspect it.
Kevin Martinez
>In article <C9EBt...@nas.nasa.gov>, bar...@otter.nas.nasa.gov (Rajiv
>Baronia) writes:
>>
>> I have recently bought an '87 Chevy Nova (clone of Toyota Corolla).
>> I had a major tune-up done after buying it; and it drives perfectly.
>> However, it failed smog due to excessive CO (carbon monoxide) emissions
>> while running at high rpm (2500). Here in Calif., the maximum allowed
>> CO content at high rpm is 1.2% , but the car is running at almost 4%;
>> and therefore it failed.
>>
>> The interesting thing is that the emissions are well within the limits
>> while running at idle; and the problem occurs only at high rpm. This
>> high content of CO and other hydrocarbons would normally indicate that
>> the fuel-mixture is pretty ritch; and should be made leaner. However,
>> the mechanic says that any tune-up/adjustment of fuel mixture would
>> only impact the idle conditions; and since the car does not show any
>> signs of excessive emissions at idle; further tune-up would not do any
>> good. He suspects that perhaps the carburetor is bad and should be
>> replaced. This obviously means big bucks for him.
>>
>> Other than replacing the entire carburetor, is there anything else that
>> could be checked/replaced in order to reduce the emissions at high rpm.
>>
>> Any pointers/suggestions would be appreciated. Thanks in advance,
>>
>> - Rajiv Baronia
>> bar...@otter.nas.nasa.gov
>It could be the EGR valve. Exhaust gas recirculation valve. It's
^^^^^^^^^
>mounted on the intake manifold and it reciculates exhaust gas back
>into the intake manifold at higher rpm, it closes at idle. It may
>be disconnected or stuck closed. Its round and about 2' in diameter
>with a small suction hose going to the top of it. Sometimes you
>can feel under it with your fingers and push up on it and feel it
>move up and down. Also you can take it off ( two bolts) and
>see if it's been blocked off and inspect it.
California Smog Check program requires the Inspector to preform a functional
check of the EGR system by verifying that the valve does indeed open and that
the EGR passage is not blocked. A finger on the EGR diaphram will tell you if
it moves when you rev the motor by moving the throttle lever. With the motor
running at about 2500 rpm opening the EGR will make the rpms fall off
immediatly confirming the EGR passage is not blocked.
Good Luck!
--
Kevin Martinez <l...@rahul.net>
Keith Maddock (SysOp)
Check the Air Injection system - it pumps air into the exhaust manifold at
higher RPM's (it doesn't do it at idle) to promote the burning of unburned
hydrocarbons and CO..... If the AI system isn't working right, the idle
exhaust will be normal, but since the system helps the exhaust from higher
RPM's the exhaust will have higher concentrations of unburned hydrocarbons
and CO......
This could be anything from a faulty air pump to a defective valve in the
system...... My car's anti-backfire valve is broken, (that's what tells the
system not to inject air at low rpm (because it makes the mixture too rich
and it ignites in the exhast system!)).
Let me know if you want more info on this - I'll type some out of my book -
I have one for '87 corollas - same engine as Nova...
------------------------------------------------------------
Keith "Bob" Maddock aka pchaos!kei...@pail.rain.com
Between Beaverton and Portland, Oregon, USA
1977 Toyota Corolla SR-5 Liftback. "Faster than it looks!"
Peter Tong
You should make sure that all vacuum lines are secure and not leaking. If
one is leaking you might have the correct co at idle but at higher rpm the
car will run slightly too rich. Slightly depends on how bad the leak is.
I'm talking about small leaks here as anything big and the engine will idle
like a pig. Just small adjustments. Other than that I would go with the
carb rebuild like you mentioned.
Peter Tong
'82 2.0 8V VW Convertible