Engine Vibration and Misfire: Possible Causes?
 

Hello all. Tonight I started my buddy's Ti after doing some work to it. We replaced the following:

Spark plugs (Bosch super, pre-gapped)
Wires
Coilpack
Cam position sensor
Valve cover gasket
Oil pan gasket
Water pump
Thermostat
Radiator
Radiator hoses
Air intake boot
Engine mounts
Suspension
Brakes

The car has been sitting for about 3 weeks. It started right up and the idle seems steady, but I am hearing what I am pretty sure is some misfire action at the tail pipe and the engine seems to have a little bit of excessive vibration. I ran the engine for about half an hour while waiting for the fan to come on (flushing coolant system). I had a look around and read several posts about misfire issues and rough running issues, but most of them don't have any resolution or follow up posts that tell how the problem was fixed. At the moment there is no check engine light.

While it was running, I went over the bay several times checking for loose connections or something that might have not been plugged in and didn't find anything. Any ideas about what I should check first? Second? Third?


Thanks!

After the list of things you've done, if there really is a misfire then the injectors are where I would start.

But (not being able to hear the car myself) if there is no CEL, I'd tend to trust the ECU and believe that there isn't a misfire.

How much have you driven the car? When I started test driving ti's early this year one thing that surprised me was that they seemed to run rough. Not so much like a misfire, but just rougher than I would expect (especially at idle)- and every ti I drove was like that. Turns out my basis for comparison was an M3 with an I6 (S50) engine. I've come to believe that the I4 (M42/44) just does sound rougher than a comparable I6. I've owned a ti for several months now and have thoroughly checked it over, and have no reason at all to believe there is a misfire or anything else is amiss- but it is still a bit rougher than I originally would have expected.

Do you normally drive a ti, and does yours sound quieter?

Check the air lines running to the injectors. When mine started cracking I got misfire issues. Also check the torque on the bolts holding the intake manifold together.

I've heard these engines tend to run better with NGK plugs than Bosch, not sure why but it's something to consider

I've never seen a perfectly smooth running M42 or M44. They all have a slight ruff idle and pop in the exhaust due to the cam timing. BMW tried to get it smoother by dialing out on the cam exhaust degree which hurt a little performance but smoothed the idle a little more. Just my personal experience I've never got mine to idle 100% smooth alway a little pop out the exhaust and tiny shake here and there


Forgot to add my car always idled and ran the best with cheap autolites. Stock and full out turbo....I've run bosch, NGK 2 & 4 prong....they suck and caused mis-fires on my supercharged applications

Thanks for all the replies guys. I haven't had too many chances to drive a ti so I don't have much base for comparison except my m20 powered e30, which is apples to oranges. It's been close to a week now and there is still no check engine light so I'm gonna go ahead and chalk it up to being normal for the good ol' m44 like you guys said.


I really appreciate all of you guys taking the time to respond. Forums with guys like you are life savers and what make being a car enthusiast bearable when things aren't working out.

Follow ups are good.