random misfire on 2003 Ford Expedition

My check engine light is on and had diagnostic read random misfire but I just had all my coils and plugs replaced last April. What next?

by in Harrison Township, MI on September 17, 2009
1 answer 1 comment
ANSWER by on September 17, 2009
Check your fuel trim numbers. The Diagnostic read was not really a full one. You need to check the Fuel Trim and other data values. There is much., much more going on than just checking for the presence of codes, and if there is a code, you need to study the context of the problem. You may have a LEAN misfire which will set a P0300 which is a random misfire. This can be caused by small vacuum leaks, worn but not yet failed sensors etc This is a common code on your engine, but there are several things that can cause it, so with out a real scan of your system, you and I are still not sure of the cause of the problem. It is best to have an Emissions expert look at this type of Code. I do Emissions work in California, and I see this type of stuff every week. A person who does not really do emissions work will be puzzled by this. Ask for a shop with a really good Emissions Diagnostic Tech.
COMMENT by on July 26, 2011
could a fuel filter cause this probem too because the filter has not been changed the cars whole life 182,000 miles
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