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I have a 1999 C5 LS1 manual, 70,000 miles all original driven less than 50 miles a month. The engine sputtered, and misfired a dozen or more times under normal operation (no codes or check engines lights)
Fuel additive was added and ran through the next tank of fuel. Ran good at normal operation, drove the interstate put some miles on it and before I got home it developed the random sputter and misfire again, but still no dash lights or codes. Parked over night, next morning started fine, minor miss/skip but ran good under normal/hard acceleration. Got on interstate cruising in 5th or 6th gear, accelerate normal and the engine began to skip and randomly misfire. Used spray bottle of water, #8 exhaust cooler than others no dash lights, showed misfire cylinder 8. (everything original other than plugs, MSD wires and OPS that were replaced within the past two years) Started replacing the older sensors and switches.
Replaced fuel filter, coil packs, plug wires and 24lb fuel injectors. Test drove, exact same result, but this time a check engine light. Computer displayed cylinder # 8 and random misfire. (the rocker covers were removed, no loose rockers, all lifters holding pressure)
The service completed - checked or replaced - Crank and camshaft position sensor replaced - MAP, OPS and Knock Sensors replaced - All 4 O2 sensors replaced - checked for vacuum leaks - checked ground and wire harnesses for issues. Completed repairs, test drove and again - ran the same, random sputter and a random skip. (no check engine lights) ( this time codes displayed Mass Air Flow and Knock Sensor - Low Circuit (knock sensors are new) (2 weeks ago while changing parts, code P1635 appeared once, cleared and has not returned)
Please, help I'm at wits end. Thanks you - Joe
Last edited by jbmcdonald; Apr 4, 2024 at 08:55 AM.
Reason: added addition information
I have a 1999 C5 LS1 manual, 70,000 miles all original driven less than 50 miles a month. The engine sputtered, and misfired a dozen or more times under normal operation (no codes or check engines lights)
Fuel additive was added and ran through the next tank of fuel. Ran good at normal operation, drove the interstate put some miles on it and before I got home it developed the random sputter and misfire again, but still no dash lights or codes. Parked over night, next morning started fine, minor miss/skip but ran good under normal/hard acceleration. Got on interstate cruising in 5th or 6th gear, accelerate normal and the engine began to skip and randomly misfire. Used spray bottle of water, #8 exhaust cooler than others no dash lights, showed misfire cylinder 8. (everything original other than plugs, MSD wires and OPS that were replaced within the past two years) Started replacing the older sensors and switches.
Replaced fuel filter, coil packs, plug wires and 24lb fuel injectors. Test drove, exact same result, but this time a check engine light. Computer displayed cylinder # 8 and random misfire. (the rocker covers were removed, no loose rockers, all lifters holding pressure)
The service completed - checked or replaced - Crank and camshaft position sensor replaced - MAP, OPS and Knock Sensors replaced - All 4 O2 sensors replaced - checked for vacuum leaks - checked ground and wire harnesses for issues. Completed repairs, test drove and again - ran the same, random sputter and a random skip. (no check engine lights) ( this time codes displayed Mass Air Flow and Knock Sensor - Low Circuit (knock sensors are new) (2 weeks ago while changing parts, code P1635 appeared once, cleared and has not returned)
Joe, well if you want to drive the car to the Gulf Coast I'd be happy to look at the car for you...no parts cannon fired here and it looks like you fired it...one diagnosis and one part...I use the most advanced diagnostic equipment (scope,pressure transducer and others) 99.9% of dealerships or repair shops don't even use.
1999 C5 Intermediate Misfire - HELP
