My 318 bmw starts perfect but sometime then runs on 3 cylinders and mis fires after a few mins clears changed cold start coil packs plugs garage can't find a fault showing nothing on anolizer

SOURCE: poor starting problem bmw 318 ti

WARNING! Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when you are near the battery or engine. A battery is filled with explosive gasses that can ignite when extreme heat or a spark is present. A battery could have residual acid on the outside casing so use caution when handling a battery and the surrounding area. Use baking soda to neutralize any suspected acid residue before work begins.

You can check the car battery using a multimeter or voltmeter an electronic one is preferred , connect the black wire to the negative side (-) and the red to positive , WARNING :DO NOT CROSS THE RED AND BLACK WIRES OR SHORT CIRCUIT THE LEADS OF THE BATTERY OR MULTIMETER YOU CAN GET SERIOUSLY HURT!!!!! you should also get a spare watering can and fill it with water ,  (dont reuse for other purposes for safety) and remove those little tabs (usually around 4 or more) and fill it up very little in each tab/cap make sure you DONT fill it to the top. The good condition of a battery is 12.5 and 12.8 volts on the multmeter and when the car is started it
(not driven just started) should around 14V which shows that your alternater (acts as battery charger when driving) is working properly.

SOURCE: 2001 (3.2) Concorde hard starting

put gas in it

SOURCE: 2002 ford f150 mis fire

Which engine?

SOURCE: mercedes c200 elegance 1996 model mis-firing on cylinders 1-4

I beleive your firing order is 1 3 4 2. 1 and 4 are companion cylinders-meaning the piston is up or down at the same time i.e. compression and exhaust stroke both pistons are up and even on the exhaust stroke the ignition fires in order to burn unburnt fuel/ h ve you checked your trigger. There is a good coil testing tool that is placed over the coil and has a magnetic pickup that allows you to see if the coil is being triggered-just because you have power doesn't mean that you will have spark. I would replace your ignition wires and look at your wiring harness very carefully- if it is very brittle and you see bare wires exposed that is your most likley problem because the trigger is working for 1 and 3 and has the crank senser input for all for spark plugs and the cam senser is used for ignition advance and your fuel injection system. try wiggling your harness and see if your coils start to work. wireharnesses are a major problem on mercedes benz vehicles of that era. I hope I have been helpful

SOURCE: 1998 ford ranger, number 3 cylinder mis fires.

When you change the plug what color is the tip of the old one? This could be the answer to your problems. It should be a light beige or tan if everything is working properly.Just take one of the old plugs down to your local garage and get the mechanic to have a look at it. He'll be able to tell you why it keeps misfiring. Hope this helps.