Only when it rains, I get a misfire and the check engine light comes on (code=multiple misfire). I've replacedthe cap, rotor, wires, plugs and coil. The problem persists. I have a 4.3 Vortec.
I had the same problem with my truck...(i have a 99 silverado 4.3L also) i took off the cap, cleaned all of the electrical areas on the inside of the cap and rotor....and put a small thin layor of die electric grease on it all....then before i put the cap back on...i ran a bead of silicone around the cap surface that seats to the distributor...and i havent had a problem for the month that i have done that......hope this helps!
Our van did this also. only when it rains. we did 2 things to cure it. 1 expensive but huge difference. use GM oem cap, rotor, ignition module. 2 make sure your windsheild seal is watertight. we were getting water into our firewall junction under the dash board.
Look at the air inlet where the air filter is- maybe it gets wet while it should take only air!
I have a 2000 jimmy 2wd 4.3 vortex ..occasional ses light multiple misfires, car has a stumble before gear changes and highway speed between 1800 and 2200 rpm , also sometmes at light accel from stop. runs like a banshee at full throttle. i replaced sfi with mfi conversion, exhaust converter, ox sensors, tune up,distributer cap twice, still has stumble, from a stop if i floor it it will burn tires and take off, but normal driving is a problem . ses light comes and goes clears itself out after a day, if i let it keep missing it will come on.
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