About every 1,000-2,000 miles I get a cel for random cylinder misfires... But what I don't get is when I drive the car for about 100 miles the cel automatically turns off. Might be the coil packs or spark plugs ?

 

sounds like something is getting wet.

 

six speed and misfires.

could be caused by an engine over-rev condition.
you'll need to trouble shoot the coils, first.

 

^^ +1

 

I have spare coils I can test out. I mean I find it weird the cel would turn off by itself after about 60-100 miles of normal driving

 

Your cel turns off because after a certain amount of drive cycles, if the ecu doesn't see a fault the light will automatically turn off. Codes are still stored but the light will turn off. Scan the code, you'll need to look at the data list and see what cylinders have the highest count. Map voltage will tell you a lot also.

 

Another one bites tha dust. Leak down test will confirm my suspecions on it being the valves, wouldnt hurt doing a compression test while ur at it. If im right you will need to rebuild the heads or buy new ones. 6 speed + misfires = bent valves. Also if you happen to pass the leak down/compression tests, adjust the valves..could fix it. Im putting my money on the heads being toast. Sorry to be a debbie downer, but im a realist. Good luck brotha!

 

Save yourself the trouble of check compression and doing a leak down test on 6 cylinders. Just check your map voltage and see if the fluctuation is more thanh .02-.06 volts. If so adjust your valves. If the fluctuation is greater than .06v+ then start a compression then leak down test. Map voltage at operating temp should be .90-.95 volts and stable to within .02volts.

 

i don't believe that is as accurate and as precise of a procedure to check the valves/valve timing. yes it may work. but is it better or just as good as a leak down? no. many variables can affect the map voltage. I wouldn't put my faith in that. . do what u do..idk what im talking about or anything

 

hopefully i dont have any bend valves... but if i do i have a spare head sitting around waiting to be built

 

^nice!

just upgrade already.
your shit is fuxxed.

if it were me; I'd already have the heads sent off to be machined.

 

It's probably the easiest and quickest way to check. Map voltage is very stable when looked at properly, and is usually the first thing I look at when a customer comes in for a misfire. It's a pressure sensor, and any change in manifold pressure would be caused from hanging valves(+ voltage) or vacuum leak (more negative voltage)