2005 325XI cylinder misfire w/details.

[richbarn2]

2005 325XI random cylinder 5 misfire. Yes I did actually search through the ongoing threads. None of which were helpful. Thank you in advance for any help given. FWIW, I have been a member here for quite some time, 1995 318IS, I still own it, besides the floor rust, it's a great car.

I purchased this E46 3 months ago, 109K miles.

The random #5 cylinder misfire is the last issue I am working through. When it occurs I get a SES light and can feel the cylinder drop offline. I pull over, shut the car off and start it again, all 6 firing. Car starts and runs flawlessly and smooth except when #5 is flagged. No other codes except #5 misfire are shown.

It only happens on the highway, around 65-75 mph. If I go the back roads to work, the misfire does not occur.

I started with all 6 new spark plugs. Went about 2 weeks then it misfired again.

Replaced all 6 coils, went about 3 weeks then misfired again.

Swapped injectors, no fix. Problem stayed with #5.

Compression check - 180 all 6 cylinders.

Considering changing the coil harness, fuel pump and filter, battery and alternator, sending my DME in for testing.

An experienced mechanic friend told me he had dealt with a bad battery doing this in an E46 before. I have been monitoring my voltage, 14.3 steady, but I understand it could be too quick of a dip to see on my volt display (cigarette lighter unit). I have witnessed batteries do some pretty strange things to cars and aircraft so this isn't as crazy as it may sound. Although it's not at the top of my "do next" list.

Thank you in advance for any help with this one. I love this car, just have to work my way though this complicated issue.

[MIKYZZ4]

Check coil and injector electrical connections on cylinder 5 for corrosion or looseness.

[richbarn2]

I did inspect the injector and coil connectors when it was apart. Clean and the sockets had the same tension as the rest of the cylinders connectors. I actually applied stabilant 22 to all of the connectors while everything was apart. I have been using it for decades, was introduced to it when I worked at USAirways. Its an Electrical connection enhancer used in the aviation industry. Prevents corrosion, enhances conductivity. Really good product, quite pricey though.

[MIKYZZ4]

Maybe a cylinder leakdown test on cylinder#5 can reveal more than the simple compression check.

[richbarn2]

All 6 original spark plugs looked the same, quite clean for the mileage on the car. I actually borescoped all 6 cylinders, cylinders, valves and piston tops all looked very good. Not to mention I had 180 across the board for the compression test. Had it been lower, or if there were oil or build up in the cylinder, I would have considered an actual engine issue. This sure looks like a component or harness problem to me. But due diligence dictates a leakdown check could be done. Although at 180, do you actually think that could be the problem? Clean plugs and borescope inspection noted?

[richbarn2]

I should add that this has only occurred with the AC off and in normal mode. With the AC on or in sport mode, it has not been an issue. More info, not sure if it helps.

[MIKYZZ4]

After your additional info, a leakdown test isn't warranted, unless as a DIY for due diligence.
Your excellent inspection of possible cylinder issues, and no clear clues, has me stumped also.

[richbarn2]

Leaning towards a DME test and fuel pump and filter replacement. Deciding on which first? Probably the pump and filter, cost for pump and filter 200ish, DME test 75, 675 for a repaired/replaced unit.

[richbarn2]

Scratch that. Happened in sport mode with the ac on today. Rolling reset, fine the rest of the drive.

[richbarn2]

I even swapped the new plugs and coils in the off chance I got a bad one. No fix. Cylinder number 5 remains the problem child.

[mtnbimmer]

Leaning towards a...fuel pump and filter replacement..

Why? Quick fuel pressure test will determine if there is a problem here.

Based on all the info you have provided, it seems like all the potential mechanical issues have been ruled out. Leaves the electrical system. Focus on the wiring harness for the number 5 cylinder. Coil, injector, etc.

[MIKYZZ4]

This seems specific to cylinder #5.
Since all other variables seem to have been excluded,
Focus further down the path, such as harness.

[MarcoZandrini]

I'd check the coil connector on cylinder #3 to ensure it's very "intimate" with the harness connector. Also, what's the condition of the coil boot. If the boots are original I'd just go ahead and replace them as PM. I'd download OBDFusion for your smartphone or tablet. It allows you to log all sorts of data that can be exported for analysis in Excel. It's available in both iOS and android. iOS uses wifi, while android uses Bluetooth. Search E46Fanatics for OBDFusion threads in which jfoj has commented. He's the guru.

[Jackson42]

You're battling precisely the same problem I'm seeing in my '04 330i, except mine's on #6. I've not resorted to the borescope (I appreciate your methodical approach to troubleshooting - USAirways obviously trained you well!) but have done all the other things you have, with precisely the same results - zip. I'd forgotten about Stabilant 22 - that's a good tip for everyone on this thread, as our cars are getting older and some of the electrical connections are already starting to fret.

I wish we could find one of the original software developers at Bosch that wrote the code for this DME and lure him/her into a consulting contract. I'll bet that if everyone on this board that has this problem threw $20 into the hat, this person could make a tidy bet of change and be a genuine hero.