ls1_simpson

iTrader: (1)

got an 94 camaro with the lt4 hotcam kit, long tube headers,full 3in dual exhaust. The car has a mis in the high rpms ive changed the opti,plugs,coilpack and i checked the fuel pressure what could be wrong with it

1994Z28Lt1

iTrader: (1)

what plugs did you go with? what are they gapped at? no missing at low rpm's when lugging? how closely did you check the wires? does it tend to run better when its cool? know anyone with the same car you could swap ignition modules with?

ls1_simpson

iTrader: (1)

i bought ac delco platuim plugs gap them at stock gap. aint check the wires they was just put on the car about a yr ago there msd wires. would the ign module make it miss like that.it dont miss at low rpms it runs about the same cold or hot

moderate Z28

The coil made mine do that once.

96capricemgr

iTrader: (1)

Well stock platinum plugs were a poor choice but honestly I think your problem is the springs, they are not sufficient for the heavier LT1 valves.

1994Z28Lt1

iTrader: (1)

i would double check the routing on your wires if you have pacesetters LT's like i do you really have to be careful with the routing on passenger side especially with the #6 plug, the boot gets extremely close to the primary.

most of the LT's are very similar in their routing, so i would start there

what rpm is it missing at?

does it run really strong up to a point and then start breaking up? being as how your obdI you're probably not throwing any codes right?

ls1_simpson

iTrader: (1)

its stout till about 4100 rpm then it all over the only codes im throwing is o2s and smog but i got the smog all bypassed. ill check the routing on the plug wires because i do have pacesetter long tube headers.

ls1_simpson

iTrader: (1)

i got the lt4 springs the car didnt run like this after the cam was installed i let it set for about 3mnths and it started this crap its doing

lt170chevelle

iTrader: (2)

replace your coil. I had a very similar problem and it ended up being the coil. They rarely go out but the do tend to get weak over time. you can get a msd coil from auto parts store for like only like 40-50 bucks and is a cheap quick fix. My car would run strong until 4,000 rpms and just start banging out..i tried plugs wires and was about to change the opti before somebody told me to try the coil.

moderate Z28

Yeah try the coil. If it doesnt work, return it. I would get an MSD blaster coil.

ss.slp.ls1

iTrader: (36)

+1 on testing/replacing the coil. There is no need to run a non-OEM coil though. I had a bad high-rpm miss once, car broke up badly above 5k rpm. Pulled my opti and found one of the plastic rivets on the rotor pointer was broken. New AC Delco and the miss got better, but didn't disappear. Changed the coil for a new OEM coil, miss got better still, but still didn't disappear. Hooked up a fuel pressure gauge to the rail, propped the gauge up next to my windsheild and took the car for a spin. At crank, idle, and running, car had 43psi. But at WOT at ~5k rpm the fuel pressure sank to 20psi. Installed a new fuel pump and no more miss! I was just really unfortunate to have a bad opti, pump, and coil all at the same time.

LM97Z

iTrader: (4)

Sounds like the coil.

ElkySS

iTrader: (6)

im having the same problem. i suspect coil. even tho its a fairly new msd

96capricemgr

iTrader: (1)

Coil is possible, BUT like I said and nobody wants to listen too the LT4 springs are NOT sufficient for the HOT cam when combined with the heavier LT1 valves. Springs break in and fatigue, nothing you have said eliminates springs as a possible culprit. Those springs were used because they were cheap and in the GM parts list, those factorsdo NOT make them appropriate. The LT1 had hollow intake valve and a sodium filled exhaust, good bit lighter than te solid LT1 valves meaning they could get away with tha weak spring. Only thing it is actually good for is a stock cam with 1.6s.

Figure when an engine is sitting static you have a handful of springs sitting substantially compressed for long periods, granted they are not getting beaten on and are not being heat cycled but still near bind for months on a few is not going to be as easy on them as sitting in a box extended.

BALLSS

While it certainly could be fuel or ignition...Dwayne is right about the valve springs.

You can decide where you want to start in terms of replacing parts....it "could" be a combination of Opti and springs.

It also would help to clean up the issues throwing codes...possible PCM tweaks to disable the smog stuff you said you don't run

if you "replaced" opti, coil, plugs, wires (and they are in fact good)....springs are very likely

Ignition module...possible...confirm heat sink putty is between ICM and head.

myltwon

iTrader: (1)

coil or icm imo

possibly bad ground aswell

ls1_simpson

iTrader: (1)

thanks guys the coil is new changed it when i changed the opti i changed the icm today and it didnt help im gonna put new wires on it if that dont fix it im gonna pay someone to go all through it buying parts i dont need is getting costly. i dont think its the springs because no one else is having any problem out of them.

96capricemgr

iTrader: (1)

Most people who buy the LT4 kit are just not sharp enough to notice the problem. You wont find anyone competent and knowledgable swearing the LT4 springs are sufficient for the HOT cam. Just the inexperianced and ignorant.

Plug wires is not a bad idea, but ignoring the input saying springs are possible is. You know how many guys buy badly matched parts and within a few months have valve float issues??? It is very common and they are just like you, completely unwilling to admit it is possible, so they spend $700 on ignition parts only to still find the problem unchanged.

robsquikz28

iTrader: (246)

agree^ seen and heard this to many times on here

myltwon

iTrader: (1)

try popping the hood at night and look for arching just to rule out wires