high rpm/load miss/backfire
10-20-2009, 11:10 PM
#1
high rpm/load miss/backfire iv already posted a couple threads about this problem in the past with no help so i thought id try again before i bought an MSD opti.
its intermittent. usually happens above 5500. can hear a small backfire through the exhaust. seems to be worse when its been driven for a long time, like half an hour or more. its driving me nuts and i just cant figure it out. it started after i put my cam in.
Parts that were replaced during cam swap:
cam, LS7 lifters, pushrods, guide plates, rockers, springs, locks, seats, GM timing chain, GM opti, new design SVO red top injectors, ACDelco fuel pressure regulator
Parts replaced since problem started (not all necessarily to diagnose problem):
several different MSD coils, several different ICMs, OTVC MSD wires, several different sets of TR55s and TR6s, SPEC 3 clutch and billet steel flywheel, Moser 12, TPS, IAC, MAP, deleted EGR, o2 sensors, head gaskets, Pig tails going to: MAF, ICM, coil. PCM replaced. racetronix fuel pump and hotwire kit
anyone who has something new to bring to the table, please help.
im probably missing a couple things here and will add them as i can remember them.
its intermittent. usually happens above 5500. can hear a small backfire through the exhaust. seems to be worse when its been driven for a long time, like half an hour or more. its driving me nuts and i just cant figure it out. it started after i put my cam in.
Parts that were replaced during cam swap:
cam, LS7 lifters, pushrods, guide plates, rockers, springs, locks, seats, GM timing chain, GM opti, new design SVO red top injectors, ACDelco fuel pressure regulator
Parts replaced since problem started (not all necessarily to diagnose problem):
several different MSD coils, several different ICMs, OTVC MSD wires, several different sets of TR55s and TR6s, SPEC 3 clutch and billet steel flywheel, Moser 12, TPS, IAC, MAP, deleted EGR, o2 sensors, head gaskets, Pig tails going to: MAF, ICM, coil. PCM replaced. racetronix fuel pump and hotwire kit
anyone who has something new to bring to the table, please help.
im probably missing a couple things here and will add them as i can remember them.
10-21-2009, 08:00 PM
#4
its like the motor turns off for a fraction of a second several times in a row. it did do it on the dyno once. theres about a 200 rpm gap in the graph. if you connected a line from where it cut out to where it came back it would look completely normal. tuner told me it dropped 70 hp when it did it. still made 363rwhp which everyone keeps saying is impressive for my mods.
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10-23-2009, 07:48 AM
#8
Yeah that is normal. I've been fighting the samething and I run the msd opti. right at about 5700-5900 it miss' a few times then pulls normal and shifts. And then other times it will pull nice and smooth up there.
Ill let you know if I figure it out, Ive been through the coils and ICM.
Ill let you know if I figure it out, Ive been through the coils and ICM.
10-23-2009, 06:50 PM
#11
no i was assured by my tuner that i was getting enough fuel. too much if anything. i dont remember what my a/f was but im pretty sure it was consistant. i have the sheet at hime. ill let you guys know when i get there and find out. i checked as many grounds and powers as i could find. any hidden ones im missing?
355z28. what lifters are you running?
355z28. what lifters are you running?
10-23-2009, 08:28 PM
#13
it will barely do it when at part throttle but gets worse about 3/4 throttle and up. it has never done it any lower than 5k tho. even if i punch it at 3k it wont do it until i hit at least 5k. if i punch it at 5k it will start doing it immediatly (when it does it)