Have a Car Question? Ask a Mechanic Online.
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.
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.
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?
its a 4.2 258 cid inline 6 with a one barrel carter yf carb
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.
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.
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. ?
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.