Misfires at low RPM under load - 03 z4 3.0

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pcaponetti

New member
Hello All,

come along with me on my journey to bringing my z4 back to health after sitting for a year and a half (terrible idea).

First, the battery wouldn't hold a charge so I replaced that with the advanced auto parts special.

As I began driving the car and scraping off the rotors the temperature gauge pegged and an oil temp light turned on (with a loud beep) after only 2 miles. I pulled over and checked under the hood and gathered the courage to pull the dipstick and feel the temp, not hot at all. After starting the car again, the temp was fine, so I figured it was an anomoly, drove another mile and it pegged the temp gauge again. After going through this cycle 3 times, I figured it was just a sensor or electrical problem and went home. with the temp pegged for a mile it went back to normal temp and stayed there.

This particular issue turned out to be a leaky coolant sensor letting air into my coolant lines which I replaced and bled the system, turned out fine. I got the check engine light reset, and the temperature has been perfect ever since.

Somewhere during that coolant sensor fix I started developing a misfire in multiple cylinders. I tried replacing three of the coils that looked bad and the plugs, still misfiring at low RPM under load.

I found a post saying that it could be the fuel pump, but I'm thinking it could be that, the electrical system (corroded ground?), hole in the air intake tube, etc etc. With all of these possible issues, what is most common for the 3.0 motor?

Please help!
 
How old is the fuel in there, possibly just working through the old stale fuel? Apart from that, I would have said coils and plugs but you have already done those. I'm sure more knowledgeable people will be along soon.
 
Thanks for the quick reply! I was thinking gas and it sat for a long time with just under 1/4 tank so when I got it I filled it with premium and some heet water extractor. Since then I've gone through about a quarter tank and the problem still exists.
 
It can take a while to work through all the old gas. I cant really think what else it could be but I'm sure someone will be able to help.
 
Hi pcaponetti, welcome.

Old fuel is bad news. You can't be sure of what you're symptoms you're seeing until that stuff has worked its way out. It may have affected the injector operation by leaving a some contaminants in the works, they may need to be flushed clean. Even though the other coils looked OK, one of them could still be bad. Try replacing the best of the old ones and then moving the freed up new one around to the other coils and see if that improves anything. I'd venture that a bad coil pack is perhaps the most common cause of misfire in M54 engines.

An air leak is also a possibility, in particular the rubber intake boot that's about an 80 degree elbow with a side inlet seems to be particularly prone to splitting.

BTW, we love pictures of Z4s here, let's see what yours looks like!
 
Seems as if the problem is getting better. It might be gas, so I will drain whatever I have left and see where I am after that.

I will post a pic when I get to my computer :)
 
pcaponetti said:
Seems as if the problem is getting better. It might be gas, so I will drain whatever I have left and see where I am after that.

I will post a pic when I get to my computer :)
Click to expand...

It's the weekend, so a good Italien tune up sounds the order of the.... weekend
 
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