missing on a cylinder under accelleration

I have a '96 318is, and a strange problem started happening yesterday. While accellerating, it sounds as if a cylinder is mis-firing, if I drive with no additional strain on the engine (cruising a steady speed, or slight accel) it runs normally. Any ideas on what to check first? (spark plugs/wires, sensors)

Do you have a Check Engine Light on? If so, get the code read and report back.

Could be fuel related, spark related, or wrong air mixture. It would also help to know when cylinder is missing.

The gear light is on, but it has been on way before this issue started happening (not quite sure what that light is for). The "Check Engine" light itself does not come on

Well I suggest you get that sorted out first... might not be the engine, but an issue with the trans

http://www.bimmerfest.com/forums/showthread.php?t=99154

That light, as I said, has been on since I've owned the car. Yes, that light indicates a transmission fault, but has nothing to do with the ignotion or firing. This is a new issue that started happening yesterday, I'll just start digging into it myself since i'm being led in a different direction than what my problem is (mis-firing on accelleration)

That sounds like an ignition coil breaking down under load to me. There are quite a few other possibilities but that is classic ignition coil behaviour. As with all of these things, the thing to do would be check the codes with a reader. That should take you straight to the problem. If you don't have the means to do this you could try inspecting the spark plugs. The one that is missing will look different to the others. If you can substitute the coil pack and it goes away, there's your answer.

It's always best to read the codes before guessing and randomly throwing money at a car. I highly recommend the Peake Research R5 ($140 from Pelican Parts)

during idle and and cruise engine load is less than when accelerating hard. this is what causes the ignition system to be stressed, causing the miss.

does this occur when snapping the throttle in park?? if so, then you can try using a spark plug tester to stress the coil(s) and see which one fails.


something like this...

the threaded portion can be adjusted to max out the coil at atmospheric pressure, which is going to be closer to the amount of pressure in the combusiton chamber during acceleration. (pressure increases resistance, just so ya know...)



df

thanks for the tips guys
turns out it was a failed spark plug wire at the plug. the boot was split, causing it to arc out on cyl4.