05 330i ZHP High RPM Misfire Issue

[weytakeninja]

Hey all,
I have been having an issue with my ZHP where under load, around 5k RPM, it will misfire, and go into limp home mode. So far I have seen misfires in cylinder 4, 5, and 6, either at different times, or at the same time. I recently had to take a road trip in this car, and cruising on the highway was not an issue, but accelerating for passing, or going up hills would cause another misfire and I would lose all power, sometimes not being able to make it up hills. After the misfire, it will idle rough, almost stalling, but when I turn it off and on again, it idles fine. I also recently had the intake smoke tested to look for vacuum leaks, and replaced the hoses that were leaking. I also just replaced the fuel filter which helped, but did not solve the problem completely. Since replacing the fuel filter, I haven't seen any lean codes, but these were coming up before, specifically bank 2 system too lean. After driving it around and trying WOT, I noticed that power is not what it used to be, and if I go over around 4-5k RPM, it will misfire, so far only in cylinder 6 after replacing the fuel filter.

I did some research on what the causes could be, and most of the problems I found were parts that I have already replaced. Oxygen sensors are relatively new, same with spark plugs, and I haven't found any ignition issues. New intake boots, I plan on changing the ccv soon. I wanted to see if you guys had any ideas on what the problem could be. I attached the freeze frame data and code data from INPA, but its all in german, so let me know if you need it translated.

I've read that clogged catalytic converters can also cause this problem, but since I live in california, I'm really trying to avoid paying $1000 per cat to replace them. Let me know what you guys think. Thanks!

[MarcoZandrini]

Is the fuel pump original? There’s a fuel pressure test valve on the fuel rail. Buy/borrow a fuel pressure gauge and check the pressure. The pressure has to be at least 50psi at all engine speeds and loads. What codes were you getting? What codes are still getting?

[weytakeninja]

Fuel pump is original to my knowledge. I’ll test the fuel pressure and make sure I’m getting 50 psi.

These are the codes I was getting before:
P3027
P0306
P0155
P0171
P2227
P0304

These codes didn’t happen all at the same time, and after replacing the o2 sensors P3027 and P0155 have been solved. I cleared the service engine light to see which ones came back and so far I have only gotten a P0306 and nothing else. I’ll keep you updated on any other codes that show up, but for now cylinder 6 misfire seems to be the only one.

Also there’s definitely a lack of power throughout the rev range, but it feels like higher range is more drastically affected. It idles and drives normally until I try to give it some gas, and I’ll noticed a dip in rpm before it begins to climb again. It also seems like it’s bogging down and having a hard time accelerating in higher gears. Again it cruises fine, but once I try to accelerate I notice the lack of power. I also replaced the vanos unit about a year ago with a rebuilt one, so that shouldn’t be the issue.

[MarcoZandrini]

Fuel pump and filter would be my course of action. Confirm with the fuel pressure test. Tape the gauge to the windshield so your passenger can watch it as you drive the car. The only fuel pump you want to buy is one made by Siemens/VDO. Aftermarket fuel pumps are junk. Replace the fuel filter also with one made by either Mahle or Keyser. The filter contains the fuel pressure regulator. Replace the 3 short pieces of fuel hose and the 6 stainless steel clamps. The filter is located under the car, under the drivers seat behind a metal panel.

[weytakeninja]

Sounds good. I replaced the fuel filter with a Mahle fuel filter, and I had to replace all of the rubber hoses because they were deteriorating and the hose clamps were also broken so those were replaced as well. I’m going to be checking the fuel pressure today to make sure I’m at 50 psi all around. I took the car out to test again last night, and I definitely noticed that the problem was much worse when the car was cold. It started misfiring almost immediately after I accelerated at a normal speed, but once it warmed up it seemed to change towards misfiring at higher rpm. I also read the codes again and this time I saw only misfire codes for cylinder 4, 5, and 6. This leads me to believe that the bank 2 cat may be clogged.

BTW this car has over 250k miles and to my knowledge mostly everything is still original, aside from the cooling system of course. I read that fuel pressure issues tend to affect cylinders 1-3 since they are at the end of the fuel rail, but I will still test it to make sure. Let me know if there’s anything else that I should look at. Thanks for your replies!

[MarcoZandrini]

It does sound like the cat could be clogged. There’s a pressure differential test that will tell you if it’s clogged.

[laxm3]

I had same issues on my 05 ZHP and turned out to be a bank 2 clogged catalytic converter. I took manifold out and had a muffler shop replace cat $300. It’s running like a champ now.