I got a 44 as per Haynes ---> Lean Exhaust - Check ECM wiring Connection terminals. Have the fuel pressure checked. Check the oxygen sensor wire. Check the carburetor gasket, vacuum hoses and intake manifold gaskets for leaks. Replace oxygen sensor (Component replacement may not cure the problem in all cases. For this reason, you may want to seek professional advice before purchasing replacement parts.) Here is what recently happened. New heads, new exhaust manifold (pass side), replaced and fixed many vacuum lines. Check engine light never came on before....but does now after about 10 - 14 minutes of freeway driving. Has always had a slight hesitation on take off, idles slightly irregular at a stop. Any ideas??? Should I change the O2 sensor and see if that helps??