Hello everybody,

I recently picked up an 03 R53 with 120k miles but it has some problems. If the car sits for about 1-2 weeks the next time I start it throws a code "misfire in cylinder 3". I put new plugs in when I got it and today when I pulled them plug 3 was all coated in black soot, the others still look great. Looking down into the cylinders 1,2 & 4 look the same; black (carbon) but cylinder 3 was "cleaner" and looked wet. Today I did a compression test and got:

1 = 150
2 = 150
3 = 160
4 = 120,130

So I was figuring it must be the head gasket but these results kind of threw me. If it is leaking into cylinder 3 I was expecting it to be the low one. I never had a bad head gasket so I am wondering if this type of thing is common when it goes bad. I thought I would see if anybody had any input before start tearing things apart. Thanks in advance!

 

First of all check your coil pack, terminal for cylinder # 3. Frequent source of corrosion and resultant misfire.

 

Yep back of the coil pack, I add a little electrical grease to help.

 

All new plugs and wires. Cleaned all connections on coil and used dielectric grease. Again, it only has a misfire when first starting after sitting for a week or more. If i let it run for a bit and restart it runs OK. If i drive it every day it runs OK. Im more concerned and confused about the loss of compression in cyl4. What is the best way to determine the source of the loss? I guess it looks like a big job any way I slice it...

 

All i can think is a leaking valve stem or a slow leak. Sticky valve? I would d a leak down test.

 

How's the car's performance? If you have a clogged cat converter it can affect the cylinder compression pressure readings. It will also mess up the fuel trims which could explain soot build up.

 

I had a clogged cat recently, car made 0 power, but I got no codes.

Leak-down test is the best way to verify. Go to your local auto parts store and rent a leak-down tester, cheapest way to find out.

I wish you the best of luck.

 

oops wrong thread

 

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