98 318ti - P0304 cylinder misfire

[hvfaith5]

I need your help. The car/engine is running rough/shakes and when pressing on the gas the engine hesitates then finally would rev smooth. But when you let go of the gas it return to rough/shakes sounds like a hot rod. I am getting P0304 cylinder 4 misfire. I have checked the spark plugs (replaced) the spark plug cables replaced last year (and also checked that they are ok). The #4 spark plus smelled like gas while the other 3 were ok. Checked and verified the ignition coils are fine. Checked the air intake and for vaccum leaks but have found no leaks. Remove the idle sensor and no change to the car/engine shake. But it addedd code P0100/P0120. Reconnect the idle sensor and reset the codes. After a few minutes the P0304 code returns.

[ATF]

http://www.obd-codes.com/p0304

Sounds like you've checked most of the solutions. I'd triple check everything thoroughly, even run a compression test.

[hvfaith5]

Here's an update and or addition. There was oil on the no. 1 & 2 spark plugs as I pulled the rubber boot. So there is a vacuum leak. But why the code P0304 (no 4 cylinder misfire). This morning I took the no. 4 wire off the spark plug and started the engine, and the problem stayed the same. Took the no. 4 wire removed the no. 3 wire and plug the no. 4 wire to the no. 3 spark plug and started the engine, still no change. Which means the no. 4 coil and wire is fine. HELP....still looking for solution.

[blndweasel]

Could be the fuel injector for that cylinder has failed and is pouring gas into the cylinder, and it's too rich to fire? Just a stab in the dark...

[mohaughn]

Originally Posted by hvfaith5

Here's an update and or addition. There was oil on the no. 1 & 2 spark plugs as I pulled the rubber boot. So there is a vacuum leak. But why the code P0304 (no 4 cylinder misfire). This morning I took the no. 4 wire off the spark plug and started the engine, and the problem stayed the same. Took the no. 4 wire removed the no. 3 wire and plug the no. 4 wire to the no. 3 spark plug and started the engine, still no change. Which means the no. 4 coil and wire is fine. HELP....still looking for solution.

Oil on #1 and #2 is a common problem. The spark plug gaskets, and the valve cover gasket need to be replaced... That won't cause symptoms of a vacuum leak.. Might cause compression to be a bit low for those cylinders, but that is it...

There is no way to isolate the coils on our cars. On the i6 cars you can move the coil from one spark plug to another and the problem will move, in our cars there is no way to change the #4 coil to the #3 coil as it is an all in one coil pack. If you take the output wire from the #4 coil output and plug that into the #3 spark plug, it should detect a misfire as #3 is firing when #4 should fire... That test is intended for cars with seperate coils, not coil packs. If I'm wrong on that, somebody please correct me, because that is how I thought it was..

[bmwgeoff]

well it sounds like you checked most of the basics. with the plug wet of fuel either the plug isnt firing or the injector is leaking or has a piece of crap stuck in it. listen to the injector for a clicking sound. this should sound the same as the other 3. also if you can get a hold of a fuel pressure gauge hook it up and watch the pressure. it should not drop more than 5-8 psi in 30 to an hour or so. if it drops quickly isolate just the injectors by clamping the return line. if it still drops then you probably have a leaking injector. Now as for the coil pack i would use a screw driver grounded to the body and carefully pull the wire for cylinder 4 at the coil away from the coil with the car running. grounding the spark with the screw driver so it wont damage the coil see how strong the spark is and how far it jumps from the coil to the screwdriver. then compair it with the others. just make sure you use a jumper wire connected to the screwdriver and a good ground. I have seen people ruin coils for not grounding the spark. this will tell you if the coil is firing properly because i believe the computer has built in coil drivers telling the coil when it should fire.