Join Date: Dec 2008
Location: Tyler, TX
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Does your 2004 4300 have a 2004 emissions (EGR) engine, or the pre-EGR DT? That's very important to the solution.
My guess from afar is that you have a pre-04 DT (non-EGR) engine and that one of the injector o-rings has failed allowing oil to leak into the fuel system.
EASY check, open the tank and see what color the fuel is. If it's greenish/amberish it's OK, but if it's brownish/blackish, well you have an injector o-ring leaking.
The "check A/C light" has many causes. Common ones include: Loss of charge, corroded terminals at the refrigerant temp sensors (two small sensors in the A/C piping on the RH side of the cowl under the hood right near the hood bumper), or a programming problem in the body controller that tripped the system off from high head pressure (common with a viscous fan drive and hot, humid days - this is fixable with a quick reflash).
By far the most common are the temp sensor terminals corroding and low charge.
'93 F-250 HD, 7.3L IDI, 5spd - FARM TRUCK
I Support: Trailer brakes an every axle over the towing vehicle's GVW; CDLs for RVers; Safety inspections for ALL vehicles and 6 axle trucks (97K GVW proposal).
Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote - Benjamin Franklin
I vote for LIBERTY!