Cylinder 4 low compression paired with misfire - Nissan 350Z Forum, Nissan 370Z Tech Forums
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post #1 of 7 (permalink) Old 06-21-2016, 09:49 PM Thread Starter
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Cylinder 4 low compression paired with misfire

I've got a 2003 touring with 101k miles on it. It's got a few mods such as a plenum spacer and exhaust manifold. A few days ago out of nowhere the car started to misfire pretty badly when I started it up. I had it towed to the dealership because I didn't know what kind of stress it would cause to drive it the whole way and they told me that cylinder 4 had low compression at 140 psi compared to the other two on bank 2 which were at 185ish each. They also told me that the spark plug was completely fouled and that the electrode was completely covered in carbon.
So at that point I decided to take the car myself to save money and replace the spark plug and see what happens from there. Well, after installing it, the cylinder was still missing pretty badly. In the past few months I've replaced all my injectors and coil packs, and I put in NGK iridium plugs at 96k, so I thought it was kind of weird that 5K miles later the spark plug is ruined.
Now I'm stumped. The car is still misfiring but I've replaced all the usual culprits. I haven't performed another compression test yet but I plan to whenever I can. As of right now my symptoms are:
-CEL light with code p0300
-misfire in cylinder 4
-low compression in cylinder 4
-white smoke in exhaust
-running rich and strong gassy smell

I'm thinking it's either my head gasket or my piston rings because those are pretty much the only other seals in the cylinder. I need to know what you guys think it is and what I should do to fix it as soon as possible because I'm moving soon and can't take the car with me.
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post #2 of 7 (permalink) Old 06-22-2016, 05:11 AM
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Have you noticed if the car is losing coolant? As that would be an indicator of head gasket failure. If its piston rings then you would be able to smell oil coming from the exhaust fumes.
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post #3 of 7 (permalink) Old 06-22-2016, 07:48 AM Thread Starter
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Originally Posted by Jinxter View Post
Have you noticed if the car is losing coolant? As that would be an indicator of head gasket failure. If its piston rings then you would be able to smell oil coming from the exhaust fumes.
I'll check it today. It's sitting at the dealership parking lot. Doesn't the white smoke indicate either oil or coolant is burning?
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post #4 of 7 (permalink) Old 06-22-2016, 08:41 AM
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White smoke usually indicates water/coolant is burning. Black smoke indicates oil in the combustion chamber.
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post #5 of 7 (permalink) Old 06-22-2016, 09:14 AM
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I would agree with dkmura. Although Iv had a turbo oil seal go on a Toyota Starlet and it gave out white smoke but wreaked of oil. That's why I suggested the smell.


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post #6 of 7 (permalink) Old 06-22-2016, 10:58 AM Thread Starter
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Alright well I was looking around the site and I saw a couple threads of people who also had low compression but they were saying their bad cylinder was at like 30 psi and the rest were about 115-120 and we're still firing. Since mine is still at 140 it should be firing still so maybe the low compression isn't the main issue. I mean is definitely not helping but at least it still holds 140.
Also when I pulled the old spark plug it was covered in fuel so I don't think my injector is clogged. I'm gonna try testing the wires leading to the coil pack with a multi meter.
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post #7 of 7 (permalink) Old 06-23-2016, 01:12 PM Thread Starter
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As it turns out, the dealership lied to me. The technician said he took out all three spark plugs on bank 2 and said that cylinder 4 was the bad one. Well I took out 2 and 6 to check them and they were both as bad as cylinder 4. So I replaced all three and the car runs fine now. They must have all been fouled because the car runs a bit rich on bank 2 (I've gotten a couple codes in the past but never had the money to get a tune). So it looks like I'm done with it. Once it gets a tune the plugs shouldn't be getting doused anymore. Thanks for yalls help!
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