my car has developed a slight misfire off idle to about 2500 rpms under light throttle. give it a little more gas (which cause of the stall takes it above 2500 RPMS), its fine. it also isnt noticeable once the car is hot, its mainly when its cold. no CEL. its getting worse now. the tune hasnt been messed with in over a month, and this only started maybe 2 weeks ago.

things ive check
-spark plugs (ive looked at them, and got a set on order)
-plug wire resistance (nothing too high or low)
-fuel injector resistance (just incase)
-compression test; most were 200-210 with cyl # 3 being 195 (done on a cold motor that sat overnight)
-sprayed carb cleaner looking for a vacuum leak but didnt find anything
-removed valve covers to look for broken springs; nothing
-no popped fuses under the hood
-cleaned the maf
-fuel pressure is good
-disconnected the O2s, problem still happened
-disconnected the MAF, problem still happened


i also tried measuring the resistance of the coils, and found 1 coil with about 2K more ohms of resistance on the outside set of wires. all the rest were about 48K, and 1 was 50K. i dont know if we can really ohm check these coils though


the motor is a built 402, ported AFR heads, 230s duration .600 lift cam, kooks LTs, ported fast 92, vararam intake. overall maybe 5-6K on the motor. also between the cam and the stall (3800 PT yank) the misfire table was set to the max. the only way i would actually get a code would be if i turned it down some (which i cant do right now because my wife has the laptop back in the states)

 

What are you setting your multimeter on? And what style of coil pack do you have?

 

how could you drive it with out the maf and 02's even hooked up? You run a speed density tune or something?

 

i didnt drive it. i just unplugged it and gave it a quick rev and it still had a misfire, so i turned it off and plugged it back in. it wasnt running more than a few seconds


my multimeter has an auto range function, so i just set it to ohms. they are the stock LS2 coil packs

 

UPDATE:

I changed my misfire tables around and cyl # 2 and 6 are having problems. i tried moving coils around as well as wires with no luck. i had just installed new plugs and O2s before that.

next thing im going to try is moving around the injectors and seeing if that does anything. if not, someone suggested it my be a PCM cause they had the same problem. it wouldnt suprise me if its the PCM as ive had problems with it already. sometime after the 402 went in it developed a rolling idle. the shop tried everything to fix it and ended up having the dealer reflashing it to stock, then reloaded the tune and it went away. only problem is i dont have access to a tech 2

 

im having a similar problem on my forged/built LS1. except mine only does it when its cold. if i let the car idle for more than 10 minutes. i can drive off with no problem.

if i fire the car up cold. let it warm up for about 3 minutes or so, drive it i have an extreme misfire around 2500-3000 rpms... i give it more throttle it goes away, i drive it 1/4 mile it goes away after and, its non-existant under WOT. also, the car does NOT throw a misfire code. im thinking coils, but i have yet to take the coils off my 5.3L tahoe to test it out.

 

You listed alot of things you checked...only thing I can add is the spark plug wires may be touching or very close and are banging into the exhaust manifold pipes. That will cause misfires, usually mid-rpms to high-rpms.

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its a little late, but i found the problem shortly after that last post. it turns out it was a broke spring. i missed it the first time cause the broke part of the spring was pointed towards the rocker, and the spring had twisted together so the other side looked normal. i rechecked them after i heard a slight tick when i started it up.