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Chris
Chris, Auto Service Technician
Category: Car
Satisfied Customers: 13883
Experience:  43 years of automotive repair, Smog license
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amc concord: hi chris , im still trying to smog my 1978 amc

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hi chris , im still trying to smog my 1978 amc concord. last time i talked to you i was getting a carburetor for the ol girl. first one was bad second one was the charm in this case. put it on ran great but when i went for my second smog it still failed. the only thing still off was c o which i was hoping the rebuilt carb would fix. The numbers went down from 15 mph-at3.75 to3.12/ 25 mph-2.47to2.05. the smog man said a catilytic converter wouldnt make up that much difference in c o, im in a quandry as where to go now,got any ideas?

Well, it is possible that the Oxygen sensor is weak, and causing the feedback system to keep the mixture too rich. If you have not tried and O2 sensor, then that would be the next step. Another thing it could be is an evaporative emission purge solenoid that is stuck open and richening things up too much. Try the O2 sensor next.

Chris

Customer: replied 5 years ago.

i dont think there is o2 sensor on this old a car is there? if so where is it located?

Well, I think there is, but let me double check that and get back to you.

Chris

Customer: replied 5 years ago.

thanks for checking chris , i am not sure.

Does your engine have the 4.2 six cylinder engine with a 1 barrel or 2 barrel carburetor?

Chris

Customer: replied 5 years ago.

its a 4.2 258 cid inline 6 with a one barrel carter yf carb

Ok thanks. Let me check this out.

Chris
Customer: replied 5 years ago.

Hi chris , I m waiting to see what you found out about the o2 sensor on my 1978 amc concord. Im beginning to believe that even if i put a rebuilt engine in this old car its still not going to pass smog because i keep hearing "the state of california wants these old cars off the road" This car is rare and its breaking my heart to think maybe its doomed to the junk yard because california wont let put her back on the road.

I looked in All Data and can't confirm this yet. I am going to look in my emission manual. I will let you know asap.

Chris

Ok, found it: Your 78 does not have an O2 sensor. They were not used on that model until 1980. Sorry to mislead you. So we can eliminate that as a cause for the rich condition So that leaves a possible evaporative emission system problem (purging fuel vapors constantly), or a carb adjustment. Another thing to consider is fuel diluted engine oil. Changing the oil and filter may help if the oil is diluted with fuel a bit, so consider that also.

Chris

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Customer: replied 5 years ago.

would changing the filter in the evaporative emission canister help? after this car failed smog the first time and was documented as a gross polluter they sent me to a test only facility, these guys dont mess with anything as far as adjustments, just run the test. so should i lean the carb out as much as possible before the next test? I replaced the carb, new fuel filter,new plugs,new air filter changed the oil and filter. the carb was engine tested before delivery and set to factory spec. if im running 3.12 co at15 mph isnt that about 3 times higher than what it should be? Even though the car runs pretty good , I determined though a compression test that the head is a little faulty and its leaking a little oil through the valve stems. when you drive it the valves go clickity clack, so i know the valve lash is a litte wide. If theres problems in the head would that affect c.o. ?

No co would not be affected by cylinder head issues. That could affect hc however. I think at this point if you cannot get the carb leaned out enough, then throw a new cat on her. If the cat i's weak and worn out then that would cause hc and co to rise. I know you said that the smog tech does not think it will help , but I think it will.

Chris
Customer: replied 5 years ago.

what might i try to correct a possible evaporative emission system problem?

Just make sure that the evap purge solenoid is not stuck open and pulling vapors from the canister constantly. Also make sure that there are no cracked or broken hoses or lines.

Chris

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