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Need help with 4.3

Cstiles90

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Cstiles90 New Member

Cstiles90

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I really need some help  I got a 99 Silverado 1500 with 4.3.its throwing a p0300 .it's had a full tune up.including the coil and icm .the distributor is good.fuel pressure is good .the cam retard is good..maf is good.tps is good.egr is good.o2s are good.i have upgraded the injectors.i changed the crank and cam sensors...according to misfire counter 80  percent of the misfires are on cyl 2 and 5.on the misfire counter it appears the misfires are only happening at 12-1800 rpms.i barely get a misfire sometimes at idle but  but none 1800 rpms and up on the counter when I'm idling.when I'm driving I really only get misfires on the counter when I let of and barely give it gas cruising on the highway.the service engine light has even flashed at me when doing this rarely but it has and I couldn't feel a miss when it was flashing.the only time I can feel like a small buck is when acceleration on mid throttle about 1800-2500 rpms.its like it cuts out barely for half a sec and goes right back but other than that nothing and that's not even where I'm showingisfires at.i have sprayedbthe intake every possible way with carb cleaner without finding a vacuum leak.have also blew ciggarette smoke down the brake booster line with no luck.i check the compression on about 4 of the cylinders that were showing a misfire and they were about all 165psi.the only sensor I haven't messed with is the knock sensor but I don't thank it would cause a misfire.im out of ideas on it

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