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1998 GMC K1500 CEL on towing uphill
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WestCoaster
1998 GMC K1500 5.7 liter VIN Code "R", CA emissions, 64680 miles, 3.73 final drive, automatic trans. Truck runs normally on flat and level and up grades by itself, but upon towing trailers uphill, CEL comes on and engine performance begins to drop off. Scanner indicates random misfire #4 with codes P0300 and P0304 in memory. Primary and secondary ignition checked, and cap, rotor, wires replaced. Primary and secondary fuel components from in-tank pump to intake crab and injectors diagnosed to have no problems. Problem persists. Preliminary TSB #1539013 mentioned in Motor Age magazine indicates in-spec but overly tight exhaust valve clearances causing misfire upon heavy load conditions. Borescope inspection of all cylinders and exhaust valves show no significant carbon buildup. Small ring of deposits seen on valve stem-to-guide interface. Anyone experiencing this problem and what is solution? Next step for me is to teardown and inspect for tight exhaust valve clearance on #4 especially. Help?
Rich
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