2003 chevy silverado 4x4, 2500 series 158,000 miles
Well taken care of, gets all scheduled maintenance, tuneups, flushes, etc etc
I drive it about 18,000 per year, and it is heavily loaded- a veterinary unit is on the back.
regular gas mileage is about 14, now about 10.
Check engine light started blinking about 1 mo ago. Computer said it was misfiring. It got a tuneup/plugs/wires/air filter/fuel filter. No change.
Tried repalcing 2 sticky fuel injectors, fuel injector flush, no change.
The blinking light is on from the time the car turns on until I turn shut it off.
Any ideas what to check next?
Blinking light means shut it off immediately to prevent damage to the catalytic converter. WAY too much raw fuel is going into the exhaust. You will likely find the converter is red hot. You hit one common cause already with the spark plugs. Another one that is only common on GM vehicles is a leaking fuel pressure regulator. Remove the vacuum hose and check for fuel leaking past the diaphragm. Another problem that only affects GM engines is mismatched fuel injectors. They just grab a handful of injectors from a bin and pop them in on the assembly line. They work fine but flow at different rates. When one is a little lean, it introduces unburned oxygen into the exhaust where it is detected by the oxygen sensor. The Engine Computer responds by requesting more fuel to all four cylinders on that side of the engine. This is a real common cause of poor fuel mileage, high emissions, and intermittent misfires, but since this came on suddenly, suspect the leaking regulator. If it's leaking badly enough to turn the catalytic converter red hot, the clue would be both of them are getting hot. An injector problem will usually cause just one to get hot. The only cure for injector problems is to buy a set of rebuilt injectors, not new ones from the dealer. Rebuilt ones are flow-matched to prevent the misfire condition. Chrysler gets their injectors from Bosch in flow-matched sets and problems in those vehicles is unheard of.