lq4 missfire / tacking sound
07-28-2012, 11:49 PM
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Staging Lane
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lq4 missfire / tacking sound i have a 2004 1500 LS extended cab silverado 2x4
it came with a 4.8 with 706 heads
the day after i bought it from a local dealership as is i cranked it up and i had no oil pressure. i drained the oil and had about a quart of coolant in the bottom of the pan. sludged oil. after i changed it a puff of smoke came out the pipe every single time i drove it for any distance and shut it off for a bit then cranked it back up.
pulled the motor and it was massivly sludged and the valve covers were full of milkshake. the 706 heads were cracked in the oil returns in 3 places on one head and 2 places on the other.
i replaced the motor with a lq4 6.0 that supposedly had 60k miles on it. had eps in baton rouge program it upon suggestion by members here. it now gets rediculous fuel milage and rediculous power over 4k rpm.
everything is stock. it is dbw and i used the 4.8 intake and tb after cleaning all the oil out of it. ever since i put the motor in even before programming it it has had a faint tacking sound coming from the bottom end and a missfire when the motor is warmed up that does not stay consistant. mostly does it with the a/c running and sitting at a redlight or bumping the gas pedal.
it sounds to me like a lifter, i know 6.0's have a ticking sound when u first crank them up but is different. when i put a can of engine restorer (the blue kind) in it it stops making the tacking sound for about 1500 miles then starts back up and seems to missfire less. the only dtc i get is missfire detected and if i dont clear it for about 3000 miles the data stream counter in history says sometimes 20,000 missfires on cyl 1 and 8. 6 usually has about 2k and the rest below 500. could the lifters cause this? im running new delco iridium plugs and delco wires.
one thing that seemed to help it for a while was i swapped the coil rails out for the 4.8 coils but after about 1500 miles it started back up again on the same cylinders.
one other thing i noticed that worries me about the ecm is that sometimes my rev limiter is at 5k and sometimes at 6k. and the other day injector number 1 decided to stop working alltogether until i let it sit for a few hours then it started working again. the injector thing actually happened once before i had it programmed. i checked that i had it plugged in and it seemed to be loose on the connection and unplugged too easily so i took out the weather proof seal and it locked on no problem.
sometimes the tacking sound is really loud. even when the oil pressure is at 40-50 lbs on idle. and that seems to be when it missfires the most.
any ideas besides pulling the heads and replacing the lifters?
this engine sees 6k rpm every single day since i love embarrasing the local cameros and vettes in a full size truck lol.
it came with a 4.8 with 706 heads
the day after i bought it from a local dealership as is i cranked it up and i had no oil pressure. i drained the oil and had about a quart of coolant in the bottom of the pan. sludged oil. after i changed it a puff of smoke came out the pipe every single time i drove it for any distance and shut it off for a bit then cranked it back up.
pulled the motor and it was massivly sludged and the valve covers were full of milkshake. the 706 heads were cracked in the oil returns in 3 places on one head and 2 places on the other.
i replaced the motor with a lq4 6.0 that supposedly had 60k miles on it. had eps in baton rouge program it upon suggestion by members here. it now gets rediculous fuel milage and rediculous power over 4k rpm.
everything is stock. it is dbw and i used the 4.8 intake and tb after cleaning all the oil out of it. ever since i put the motor in even before programming it it has had a faint tacking sound coming from the bottom end and a missfire when the motor is warmed up that does not stay consistant. mostly does it with the a/c running and sitting at a redlight or bumping the gas pedal.
it sounds to me like a lifter, i know 6.0's have a ticking sound when u first crank them up but is different. when i put a can of engine restorer (the blue kind) in it it stops making the tacking sound for about 1500 miles then starts back up and seems to missfire less. the only dtc i get is missfire detected and if i dont clear it for about 3000 miles the data stream counter in history says sometimes 20,000 missfires on cyl 1 and 8. 6 usually has about 2k and the rest below 500. could the lifters cause this? im running new delco iridium plugs and delco wires.
one thing that seemed to help it for a while was i swapped the coil rails out for the 4.8 coils but after about 1500 miles it started back up again on the same cylinders.
one other thing i noticed that worries me about the ecm is that sometimes my rev limiter is at 5k and sometimes at 6k. and the other day injector number 1 decided to stop working alltogether until i let it sit for a few hours then it started working again. the injector thing actually happened once before i had it programmed. i checked that i had it plugged in and it seemed to be loose on the connection and unplugged too easily so i took out the weather proof seal and it locked on no problem.
sometimes the tacking sound is really loud. even when the oil pressure is at 40-50 lbs on idle. and that seems to be when it missfires the most.
any ideas besides pulling the heads and replacing the lifters?
this engine sees 6k rpm every single day since i love embarrasing the local cameros and vettes in a full size truck lol.
