i have a 306 cam lt1..when i first initial start it misses for the first 45seconds-a minute...feels like a dead miss i think on cylinder 7 and 8 at any rpm...then after warmup it turns into a random miss maybe swappinh between the 2 and runs smoother but is down on power...yall think it could be a vacume leak on back of manifold? worth checking? btw no oil leak back there

i been working on it and got alota my problems fixed with gm opti, any other ideas?

 

Since you have headers, it would be easy to find the misfiring cylinder. After the engine is completely cold, fire it up and quickly find the header pipe that is staying much colder then the rest with an infrared thermometer.

Now you can go about finding the cause a few different ways. You could swap in another plug and plug wire and see if it clears it up. You could also put an inductive timing light on it and look for a changing flash pattern.

My bet is on a plug wire firing to a nearby metal piece. Once you find the cylinder, the problem plug wire should be easy to find. If that is the problem.

If it's not ignition, then it's time for compression or leak down testing.

Another possibility is coolant leaking into a cylinder from a bad intake gasket. As the joint heats up, it can sometimes seal up as was the case on my Vortec motor I just put gaskets on. But then you should see the water level go down over time and the piston and or plug should show that as well.

 

dont see any noticable coolant loss...the wires could be arcing, but ive done an infared test and the back 2 cylinders are about 20 degrees colder after 15 seconds running? any ideas

 

Try the timing light since 20 degrees does not seem that bad.

 

toming light they all look fine...
i was running tonite and when i got to about 6000+ i had about 4 pops before it shifterd about 6700, these were what i believe to be misfires...
when at idle also in neutral i can hear it miss and it sounds as if you say "doom" real deep, and it misses about 3 times in a row constantly (same cylinder) then picks up and runs for about 3-5, then misses again....if i bring the rpm up to about 2k i can hear a miss also...this one sounds more consistant...so its like one cylinder hits half of the time at idle...and under any load it misses consistantly...
what can cause this?
it sounds like oblivously to me its either intake gasket, head gasket, injector(not leaky), spark plug, wire, distributor
underlined is what i havent checked, i dont have coolant loss and dont have burning oil i dont think, so im guessing leaky intake gasket could cause this how?
help!