Intermittent Misfire

[Nanniepoo]

This is on a '98 323is, 155k miles.

Replaced the plugs yesterday (they all looked identical and appropriately worn) and thought it fixed it, but it came back today. Originally I was just getting a slight miss occasionally when I was accelerating, but it was kind of a one and done type deal. And would get a slight hiccup at idle every once in a while, but nothing too bad. Then a couple weeks ago I floored it getting it on the highway, in 3rd around 70 it started missing really bad. Kept driving a bit because I didn't really realize what was happening and was trying to figure it out. It was fine cruising, but would shake when accelerating. Finally pulled over (in the middle of Detroit), turned the car off, and when I restarted it went away. That's what prompted me to change the plugs.

So with the new plugs, any missing at idle is completely gone. The occasional miss is still there when accelerating but lessened. But now, twice in one day it has been re-triggered by getting on it while on the highway. It seems to be constantly missing after it has been triggered. I do have a code for misfire in cylinder 2 that was there prior to changing the plugs and just checked and it's either still there or at least back now. The misfire goes away after re-starting my car, but I need to leave it off for 30 seconds or so. An immediate restart and it's still missing.

What I'm thinking, since it is just one cylinder, is if it's fuel related, I'm good through the fuel filter at least or I'd have problems in multiple cylinders. So just that one injector. Could be ignition since it's improved with the new plugs...maybe the stronger plug is helping out a worn ignition coil. I have new boots I can put in tomorrow, and will test the coils. I have BavAuto "high performance" coils for an M50, and have heard I can cut the extra ears off to make them work on a M52, but not sure on that. Think I'd rather sell them and buy new honestly. I think last cause would be vacuum leak but since it's more of an issue while accelerating instead of idle, think I'm good there. Intake boot is brand new.

And just FYI my other codes are SAP relay and intake air temp sensor.

Any ideas? Am I on the right track (especially with my assumptions)?

[MisterM52]

sounds like the coil? Dont think it can be a injector, I guess you can always swap out the injectors..likely the coil imo..sell the m5o ones and grab the M52 ones, things as this you rather not take second chances cutting and what not.

[gcburkett]

Probably easiest to switch the coils with another cylinder to see if the misfire moves to the other cylinder. Not sure why it would take 30 seconds after shutting off to start running correctly again unless the coil is getting hot and causing the problem.

[Nanniepoo]

Well....just happened to be watching a DIY video by BavAuto on a fuel filter replacement and they said a sign is misfire/poor performance at high engine speed that goes away after the engine is off for a little while. Guessing the lines need to re-prime. Odd that I'm only getting a code for one cylinder, but I'm going with it.

Still planning on replacing the boots and checking the coils in the mean-time.

Thanks for the help so far!

[Smoky540i]

I think I may have an extra set of used coils... I'll check tomorrow

[MisterM52]

I did my fuel filter a month ago, very easy thing, not that the old one looked that old or rather too clogged, but hey, just make sure you dont let any of that fuel in your paint, ask me why..I am heading to my this guy I know just before xmas so he can touch things up and fix my little misadventure.

[Smoky540i]

Yeah fuel filters are easy on these cars. I just did mine on my 328i at like midnight, in the cold and I was dead tired.

[Nanniepoo]

Figured I'd update this while I diagnose today. Have narrowed down the symptoms a bit. Issue still there after the fuel filter change.

It varies slightly, but basically when I give it too much gas below 3k, it starts misfiring. By varies I mean how much gas, sometimes I can give it more than other times. I haven't been able to track it if it's based on engine temp or not. If I push it too hard, or don't back off in time, it will constantly misfire until I turn the car off and wait. I haven't actually timed it, but I would say if I wait 10+ seconds it's fine. An immediate restart and it will continue misfiring at idle. Driving yesterday I got on it quite a bit, so I'm able to accelerate like normal above 3k, anything from part throttle to WOT. Under normal conditions idle is rock-solid at ~750 RPM.

I'll pull codes again, but last I checked, and after a couple resets, misfire according to the ECU stays at cylinder 2. This was also consistent before and after changing the plugs. So today I'll be checking the resistance on all the ignition coils. If nothing sticks out I'll swap one cylinder with #2 and see if it follows.

And just to throw it out there, I haven't replaced the intake air temp sensor. I bought all the parts a while ago, but since I'm also cleaning the ICV and replacing the CCV, among other things in the area, I was going to do it when I had a solid day...but now it's cold so I was going to wait for spring. I was putting it off since the car originally drove fine...but since there is an issue with drive-ability I'm thinking I might as well fix what I know is wrong.

- - - Updated - - -

Well....they're all high, but close. I'm kind of assuming it's because of my cheap Craftsman voltmeter.

From the front:

1. 1.0
2. 1.1
3. 1.1
4. 1.2
5. 1.5
6. 1.0

They all bounced between 0.9 and 1.7 but seemed to settle at the values above. I switched 2 and 4 and have to go run errands in a bit so I'll see if the misfire moves.

[xlDooM]

There are failure modes which do not affect the resistance across the primary coil, so it's not because they measure ok that they are good. But you probably already knew that.

[Nanniepoo]

Also I have that torque app and bluetooth OBDII scanner...any data I should look at while driving today?

[Nanniepoo]

Misfire followed the ignition coil. Ordering new coils right meow.

[mike318]

My sons 92 325i has low speed engine missing also, but no codes are produced. Fuel filter is new. The coil multimer reading were in spec too. Would you say it might be the cam sensor, I hate to throw money at it. Thanks in advance. Mike

[Nanniepoo]

My sons 92 325i has low speed engine missing also, but no codes are produced. Fuel filter is new. The coil multimer reading were in spec too. Would you say it might be the cam sensor, I hate to throw money at it. Thanks in advance. Mike

It could be. That did come up in my research.

Unfortunately doesn't look like there's a way to test it.

Have you checked for vacuum leaks?

[mgoods50]

ill leave this here just in case you have not yet bought bav autos. I saw you had a set for m50, just assuming you might buy them for this car. i HATED mine. one failed within 10k, another at abt 15k. the ordeal frustrated me so, i swapped in a set of spares.

ive also had that issue with cam sensor, ( obd1.) i did get a code though.

[Nanniepoo]

ill leave this here just in case you have not yet bought bav autos. I saw you had a set for m50, just assuming you might buy them for this car. i HATED mine. one failed within 10k, another at abt 15k. the ordeal frustrated me so, i swapped in a set of spares.

ive also had that issue with cam sensor, ( obd1.) i did get a code though.

I did go with the BavAuto ones. The M50 ones lasted me at least 30k miles with no issues. Not that that's a particularly long time since the OEM ones lasted 150k...

[mgoods50]

Well I'm hoping whatever issue they had was rectified and these will last you a long time with no problems ☺

[Nanniepoo]

Well I'm hoping whatever issue they had was rectified and these will last you a long time with no problems ?

Got them installed last night and after about 10 minutes of driving everything is running like a champ

[mgoods50]

Awesome !!

[Nanniepoo]

Just thought I'd bump this since I re-read it...one bavauto coil did fail in under 3k miles (from what I remember). Got a replacement under warranty and has been fine since.