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Help! 1990 27' Ford, 460 FI MH won't pass smog at idle. Readout indicates running rich. New Cat Conv. new plugs, wires and new air filter. clean oil. MH has 43,000 miles and passed the high RPM portion of smog with flying colors. Any idea's??
Lots of things can cause rich.Has the thermostat been checked for engine up to normal temp.O2 sensor may be getting slow or lazy.Vacuum leak at slow speeds may cause a lean misfire with unburned gass going out the tail pipe.At higher rpms the vacuum leak is a smaller % of the air intake.may not affect the fuel ratio enough to get missfire.Coolant temp sensor may be off or bad connection. Just a few ideas to check out.You may have to scan the computer to see what it is seeing. Good Luck Mike.How was the CO readings???
Thanks for the info Mike. The CO% reading at idle was 2.42. The MAX is 1.50 with the AVE being 0.20. These numbers are from the smog check emission report. Is there any of these issues you mentioned that would cause low idle as well as the richness problem? The idle (according to the report)is 543 and seems to be be low. Under the hood, a sticker states that the idle and fuel mixture cannot be adjusted. Thanks, dennis
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