QuestionQUESTION: i recently did a tune up on my 2000 gmc jimmy 4.3L changed the oil and oil filter, plugs, and plug wires. after tune up it started backfiring at mid to high rpms. misfires under acceleration from stop. has catback exhaust and KnN cold air intake kit. only misfires under hard acceleration but doesnt under soft acceleration, new plugs, new wires and oil change, all started after doing this.
ANSWER: i would take the plugs back out dry them off sand them... and put them back in. you are gettin air in somehow.. runnin lean... did any of the plugs break when you took them out?
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QUESTION: no plugs broke when i took them out. when its idling the oil pressure is normally at about 40 to 42 psi but when it starts acting up the oil pressure is at about 34 to 36 psi and the rpm's are normally at 1000 but when its acting up its at about 600. it has the correct amount of oil. and the correct oil weight.
Answeroil amount and weight has not much to do with misfire. if you are sure its a misfire its coming from the plugs OR there maybe a hair line crack in the distributor that you cant see.. if you over tighten the cap this is common. now backfiring is usually caused by a build up somewhere and again usually if you are running lean(gettin to much air in) this happens.take the plugs out are they wet on the end? if they are then you have a build up or its gettin to much air.
ill tell you what i did to a car i had that did this.
1997 chevy lumina
i replaced plugs wires disb cap belts all that and it started actin gup
so i took the plugs out every other day dried them off put them back in
then about the 3rd week i took the car out on an open stretch of road and floored it
cleaned out the carbon build up and about a week later it was back to normal
