My friend Pat Washburn asked:
>Subject: 1998 Chev 3500 Dually w/ 454 engine..
>
>Problem: Absolute sucky fuel use. I don't mean "well you gotta big
>engine, of course it's going to suck" kind of mileage. I mean like 3 to 4
>miles per gallon. Empty. Not towing.
>
>Tried: Dealer and independent repair shop evaluation. (One shop even had
>a brand new, supposedly very high tech Snap-On digital engine anylizer. No
>information from them other than "Well, the compression is good.") Result
>is that all OBDII readings are within spec. Engine has around 49,000
>highway miles. We put on a new fuel regulator, no help. (Thought there was
>a TSB.)
Check the O2 sensors -- I gotta think something is latched lean, which
causes the ECU to run the engine way rich. Running that rich will lead to
really high EGTs, too, which will kill the cats, too (by melting the insides).
>It runs great. No one can seem to figure out why this is. Can anyone
>relate any common experiences?? Any suggested areas to look at? Thanks
>gang!
Are the plugs okay? Something like this, the plugs should be nearly
dripping wet with fuel fouling. Vapor cannister purge system is another
possibility. But nearly all of these should twig something in OBD-II. Is
the crankcase full of gas? Air filter clogged? Exhaust plugged?
Check for fuel leaks, stuck injectors, the neighbor kid with the 2nd-gen
Camaro (you know the one: mullet haircut, the car has air shocks and
extended spring shackles, and the rear tires stick out of the wheelwells
about 3") that, despite $2/gallon premium in the area, has enough cash for
a new set of chrome exhaust tips for his 2" pipes, the driver who seems to
like running 4WD Low Range all the time or mats the gas pedal and regulates
his speed with the brakes, a driving regime that consists entirely of
highway speeds uphill and into the wind, and that same neighbor kid saving
gas by hooking his Camaro to the back bumper on the morning commute...
Jim Crider
autojim@att.net
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