engine spark knock

keveyj · April 16, 2006

i got a 02 chevy with a 4.8l i just put on a flowmaster cat back and i took it for a drive tonight and now it spark knocks and won't kick down does anyone know what i have to do to fix this ?

99Silver6.0 · April 16, 2006

i got a 02 chevy with a 4.8l i just put on a flowmaster cat back and i took it for a drive tonight and now it spark knocks and won't kick down does anyone know what i have to do to fix this ?

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Changed plugs, fuel filter lately? Might be a good time to blow some SeaFoam through the PCV and brake booster vacuum lines. The LSx base engines are pretty good about sending oil back up the PCV line and barfing it all inside the intake. Then putting it right on top of the pistons. Carbon buildup from that crap causes alot of knock. Sometimes its audible and sometimes it can only be seen with logging software. There are a few things to remedy the oil consumption problem if that is in fact the problem. Some simple and some are more technical. Try looking at your plugs and filter first.

Butch 02 Denali · April 16, 2006

Good recomendations above! I would also clean the mafs. That can cause both pinging and shifting problems if it's dirty or going bad.

No codes?

ChevyTech007 · April 16, 2006

Did the ping start immediately after you replaced the cat or did it do it before also?

99Silver6.0 · April 16, 2006

Good recomendations above! I would also clean the mafs. That can cause both pinging and shifting problems if it's dirty or going bad.

No codes?

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Dam, I forgot to mention the MAF!!!

keveyj · April 16, 2006

i put in on the scaner last night its saying misfire on number 3 iand no it started about 20min after i put the cat back on it and i did go thu about 3 feet of water with the truck also thanks for the help i'll check the plugs and mafs tonight when i get in the shop to put in my shift kit

99Silver6.0 · April 16, 2006

i put in on the scaner last night its saying misfire on number 3 iand no it started about 20min after i put the cat back on it and i did go thu about 3 feet of water with the truck also thanks for the help i'll check the plugs and mafs tonight when i get in the shop to put in my shift kit

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Check the wires too!

keveyj · April 23, 2006

i got the truck fixed on wensday it was the cats were pluged so until i get my new ones i cut them out the truck sounds alot better now and has alot more power