high rpm/load miss/backfire

ElkySS · 10-21-2009, 12:10 AM

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.

ElkySS · 10-21-2009, 08:00 PM

anyone?

robsquikz28 · 10-21-2009, 08:47 PM

Does the car lose power at all when this problem occurs? Has this ever happened on the dyno and you have been able to verify power loss?

ElkySS · 10-21-2009, 09:00 PM

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.

ElkySS · 10-22-2009, 12:26 AM

i have noticed that my pass. side o2 sensor has been fouling out fairly often. maybe i have a leaking injector or an injector sticking open?

ElkySS · 10-22-2009, 08:11 PM

bump...

ElkySS · 10-22-2009, 09:35 PM

leak checked the fuel system. took an hour to bleed down from 40ps1 to about 5psi. does this sound normal?

355z28 · 10-23-2009, 08:48 AM

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.

old93camaro · 10-23-2009, 09:19 AM

sounds like you running to lean up top..when you had it dynoed how was your a/f at wot

robsquikz28 · 10-23-2009, 07:27 PM

Do you a air/fuel gauge at all or on the dyno did it run lean at all near that rpm? Did you check all ur grounds to be good and all powers to be tight and have good voltage?

ElkySS · 10-23-2009, 07:50 PM

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?

67goatman455 · 10-23-2009, 08:58 PM

your title says a load miss also? describe

mine had a miss under heavy load and an occasional miss through the rpm.... my problem was the opti

ElkySS · 10-23-2009, 09:28 PM

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)

67goatman455 · 10-23-2009, 10:23 PM

its probably going to be the opti. mine did the same thing but in low RPM.

ElkySS · 10-24-2009, 12:11 AM

^^ ill probably replace it soon if, for nothing more, peace of mind

ElkySS · 10-24-2009, 12:13 AM

my a/f starts off at anout 13 and then slowly drops and ends at 12. very smooth a/f btw

robsquikz28 · 10-24-2009, 12:18 AM

so if it starts at 13 and then goes to 12 when jacked up that would mean it gets extremely rich which can cause a bog down. A/f should be around 13.2-13.8 with a tune but if it goes to 12 and back to 13 thats bad.

ElkySS · 10-24-2009, 12:46 AM

no its at 13 when when pull starts and slowly and smoothly drops to 12. it doesnt seem to be affected by the miss or even relate to it, just by looking at the dyno sheet. its almost a perfectly strait line. it doesnt go back up

ElkySS · 10-24-2009, 08:26 PM

bump...

robsquikz28 · 10-24-2009, 10:08 PM

Just askin but did you ever clean your maf at all. Being dirty can make shit run rough.