radical fuel mpg loss 1994 chevy suburban

Asked by Mar 27, 2013 at 07:27 PM about the 1994 Chevrolet Suburban K2500 4WD

Question type: Maintenance & Repair

last summer vehicle was in high heat 1oo plus degrees outside temps. battery went dead tried to jump start burned up a set of jumper cables in jump start process the cables were connected properly from ea veh battery pos to pos  neg to neg . after replacing battery the suburban started ok runs ok but have a radical mpg loss . any thoughts ?

7 Answers

94,975

I would start by checking the EGR and PVC valves. Something changed to cause that kind of drop. Maybe a O2 sensor but that have lit the CEL.

88,855

If it is a Vortec engine it could be the early signs of a intake manifold gasket failure. My Chevy started a drop in mileage, then it would ping really bad under a moderate load but no check engine light ever came on. Pulled the intake off, and sure enough the manifold gaskets were just starting to fail. replaced gaskets and everything went back to normal.

no check engine light? there should be with a problem of this nature, even the plugged EGR should toss out a warning- efficiency should be monitored....somewhere?....the built in diagnostics~

no c e l. need to check intake and other vac lines and vac operated devices for leakage and function and will check intake manifold gaskets and egr valve also will check idle air control valve as well and clean carbon deposits. thanks for your help.

egr valve can have a carbon problem and not trip a code or the I a c v can can have a carbon problem and not trip a code.

any other suggestions out there ? other jacking up the radiator cap and bring in a new veh L O L.

88,855

Hey judge it's OBD1 there was a lot of leeway on what would turn on the light and what would not, I thought that the PCV vacuum that was applied to the crankcase would overcome the smaller intake gasket leak at the time, but when you pulled the PCV out of the system and and plugged the crankcase in take tube then you slowly got vacuum back into crankcase that was the clencher for me to tear it down. If I had let it go longer it might have set a fuel management code but why wait when you now what and where to go.

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