Intermittent Misfire on my 325i Coupe with n N52 Engine

Elvin · Monday at 11:55 AM

Hi All,

So I have experience this this issue for a few months now.
The initial Diagnostics pointed to bad Coil Packs 1&2. I replace all 6 with OEM Coilpacks. 2 days later the misfire was back. Did another Diagnostics and this time it pointed to Post Cat Sensor in active. Replaced this sensor and the problem was still there but this time diagnostics pointed to Bank 1 Sensor 2. Replace that and 2 days later it started the misfire again. Did another Diagnostics and this time the fault was Fuelsys1 02Sensor OL. I started by cleaning the DME. Then the fault was only in the mornings. Please can I get an insight into this issue.

Nastaliq · Monday at 12:26 PM

Check the catalytic converter backpressure, clogged cats can cause misfire.

Have you done a compression test?

if the fault seems to be limited only to the mornings, this could be temp related, morning temps are lower than later on and therefore temp can cause issues if sensors are cold, especially the post-cat sensor and bank 1 sensor 2.

Mytfine · Monday at 12:34 PM

Did you replace spark plugs along with the coil packs ?

Nastaliq · 2025-10-01T13:53:40+0100

This bra joined the forum to ask questions, and left it when he got answers.

Elvin · 2025-10-02T09:03:47+0100

Nastaliq said:
This bra joined the forum to ask questions, and left it when he got answers.

My apologies Sir. My work day really consumes me sometimes.

Elvin · 2025-10-02T09:05:38+0100

Mytfine said:
Did you replace spark plugs along with the coil packs ?

Hi Sir. Yes I did. New coil packs and new plugs, Post cat Sensor and Pre cat Sensor as well. It was running fine these past few days but then started again this morning.

Elvin · 2025-10-02T09:07:52+0100

Nastaliq said:
Check the catalytic converter backpressure, clogged cats can cause misfire.

Have you done a compression test?

if the fault seems to be limited only to the mornings, this could be temp related, morning temps are lower than later on and therefore temp can cause issues if sensors are cold, especially the post-cat sensor and bank 1 sensor 2.

I've done everything as per the diagnostics. It was running fine for the past few days and then the misfire started again this morning.

Elvin · 2025-10-02T09:12:26+0100

Mytfine said:
Did you replace spark plugs along with the coil packs ?

Hi, Yes I did.

Elvin · 2025-10-02T09:14:56+0100

Nastaliq said:
Check the catalytic converter backpressure, clogged cats can cause misfire.

Have you done a compression test?

if the fault seems to be limited only to the mornings, this could be temp related, morning temps are lower than later on and therefore temp can cause issues if sensors are cold, especially the post-cat sensor and bank 1 sensor 2.

I'm considering a De-Cat. Any suggestions. Any reputable guys out there can do it at a decent price.

Teezoh · 2025-10-02T09:22:02+0100

Where are you based? You need to get your car scanned in order to get some sort of indication of what is actually wrong with it, no use in just replacing random shit and hoping for the best.

Yes, you said you checked and cleaned the DME but I also know there's potato software out there so you might want to give a tad more detail, what software etc. and also include the codes. Also try and be a tad more clear on your experience as a misfire, is it only on idle, on load etc.

Elvin · 2025-10-02T09:23:05+0100

About a year ago I changed the CVV Valve on the Valve Cover with an aftermarket from Goldwagen. Did I make a wrong choice with an aftermarket part? I am considering changing the complete Valve cover next week.
I also discovered that the wiring after the Oxygen Sensors that are in the harness is very hard. IT's actually brittle. Could this be another cause for misfire?

Elvin · 2025-10-02T09:27:01+0100

Teezoh said:
Where are you based? You need to get your car scanned in order to get some sort of indication of what is actually wrong with it, no use in just replacing random shit and hoping for the best.

Hello Teezoh. I have my own Scanner. Its the basic one though. The latest fault code I get now is "FUELSYS2 OL-Fault"

Elvin · 2025-10-02T09:29:23+0100

Teezoh said:
Where are you based? You need to get your car scanned in order to get some sort of indication of what is actually wrong with it, no use in just replacing random shit and hoping for the best.

Yes, you said you checked and cleaned the DME but I also know there's potato software out there so you might want to give a tad more detail, what software etc. and also include the codes. Also try and be a tad more clear on your experience as a misfire, is it only on idle, on load etc.

I'm based in Durban. I work in New Germany. I've take my car to a highly recommended BM Tech up the road from my work. He changed the sensors and brought the car back to me. it ran perfectly for 2 days and then the misfire was back.

Teezoh · 2025-10-02T09:32:14+0100

Elvin said:
Hello Teezoh. I have my own Scanner. Its the basic one though. The latest fault code I get now is "FUELSYS2 OL-Fault"

This is a very generic code, you need to get it scanned with something providing a little more detail like ISTA/D, INPA, Rheingold, Foxwell NT510, Carly, MHD logs, etc.

Teezoh · 2025-10-02T09:47:08+0100

If you can't get it scanned and really want to go the forum route I would personally start with the following order:

Smoke testing the intake and valve cover area - any workshop can do this for you or you can get creative with a vape.
Check crankcase vacuum - pull the oil cap off at idle. If it’s very hard to remove and idle changes drastically, CCV/valve cover can be the issue.

Then report back.

KPM3_30 · 2025-10-02T10:25:48+0100

Elvin said:
I've done everything as per the diagnostics. It was running fine for the past few days and then the misfire started again this morning.

So the reoccurence is effectively what brought you back and coincidentally, your work didn't consume you now.. Gotcha.

Mytfine · 2025-10-02T18:27:24+0100

Elvin said:
Hello Teezoh. I have my own Scanner. Its the basic one though. The latest fault code I get now is "FUELSYS2 OL-Fault"

Yeah bud as the members said you need a proper scan before you throw parts at the problem.
If its still random, then you need to run live logs as well.

I have had ccv cause random misfires as well as injector issues as well as dodgy fuel or bad fuel pump/pressure under load give random misfires but if you dont have the data on what the cylinder is doing when the misfire happens then its hard to diagnose.

If you cant ,
Start with the basics, remove every plug, clean with electrical cleaner, check continuity between points, pull the plugs again and read them on condition (plenty info online) swap plugs and coils around and make notes which way you did and see if the misfire moves cylinders.

Good luck to you.

Nastaliq · 2025-10-02T18:28:01+0100

Elvin said:
About a year ago I changed the CVV Valve on the Valve Cover with an aftermarket from Goldwagen. Did I make a wrong choice with an aftermarket part? I am considering changing the complete Valve cover next week.
I also discovered that the wiring after the Oxygen Sensors that are in the harness is very hard. IT's actually brittle. Could this be another cause for misfire?

sounds fishy.
If its not properly sealed, it will fail a compression test.

I agree with the comments on here, scanning with a random scanner and scanning with ISTA are two very different things.
ISTA will give you alot more information on exactly what the fault is as a likely consequence of, since this wouldnt be a random 1 off fault.

It will say persistent versus intermittent.

Get the car scanned by someone with ISTA. Dont decat till its scanned and definitely do a compression test because if that seal is suspect, it will give you errors like youre getting now.

The misfire is a cough. You dont need to stop the cough, you need to stop the cold which is causing the cough.
Figure out what conditions result in a misfire and replicate it repeatedly and then you can figure out the root cause.

Nastaliq · 2025-10-02T18:30:53+0100

Check the plugs for carbon buildup. There are specifications for the gap which is optimum. Use a feeler gauge to check that gap on the plug.
I have had misfires before caused by a plug that came out of tolerance from the box.
Looking at it, it seemed hundreds, but a feeler gauge showed it was shit. I took it back with the box and receipt to BMW and they replaced it no questions asked once i slid the feeler through and showed them the variance versus another one from the parts bin. I suppose it passed QC somehow.

Nastaliq · 2025-10-02T18:31:59+0100

Queue all the "feeler" gauge jokes.

Intermittent Misfire on my 325i Coupe with n N52 Engine

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