Yesterday, I performed an oil change in my 2003 Nissan 350z (VQ35DE). During the oil change, I installed a sandwich plate between the oil filter (for ease of installing an oil temp sensor, which is on it's way to me. The sandwich plate has NPT ports, so I won't have to tap the oil pan). The install was very straight forward and everything fit perfectly (all ports plugged for the moment, since I don't have the oil temp gauge parts yet.). Perviously, I had used a synthetic blend oil, but I had opted to use full synthetic this time around (Mobil Super Synthetic 5W-30). We filled the car with 5 quarts.
Upon turning the car back on to allow the oil to circulate, the SES light immediately came on (Service Engine Soon). The idle also seemed to be slightly more rough than usual. No oil leaks under the car. Turned the car off and back on. The light remained illuminated. I decided to take the car for a very easy test drive around the neighborhood to see if the light would go away. During my test drive, I heard a loud "BANG.......BANGBANG" sound from under the hood/engine bay area. I pulled over and turned the car off. Still no leaks. Nothing unusual in the engine bay. No unusual smells. After a lot of inspection, I hopped back in the car and began driving again. The same thing happened within 1 minute of driving. The noise was terrifying enough for my friend and I to push the car back to his house, as I didn't want to risk any more driving.
We gave the car a thorough inspection, and couldn't find anything peculiar. We removed the dip stick multiple times (wiping it clean between dips) to get an accurate oil level reading. The synthetic oil was nearly IMPOSSIBLE to see. We even tried running our fingers along the stick to see if we could feel the reading rather than see it. Still no luck, even with another set of eyes (a mechanically inclined neighbor had joined us by this point).
We ran the SES code with an OBD reader, and it was a "Multiple Random Misfires" log. After doing some research, I found that excessive amounts of oil can lead to fowled spark plugs (which could cause misfires).Since we did not know which bank/cylinder we were dealing with from the code, we decided to randomly pull a spark plug and see what we get. The plug that we pulled looked fine (no charring/oil residue). The mechanically inclined neighbor told us that it could also be due to a bad coil pack. He happened to have a new on in his garage, so we installed it for the plug that we had already removed, and took the car for another test drive. The loud "BANG" noises seemed to be cured.
There is now a slight issue with stuttering/hesitation while driving, where the RPM needle dips and then returns within a split second. I have narrowed this issue down to the 1,500-2,500 RPM range, and it only seems to occur under load with moderate acceleration (roughly 1/2 gas pedal depression). Idle is completely issue free. The car has not thrown any codes or dash lights since the coil pack was replaced. I have also noticed that the oil pressure is significantly less than it used to be before the oil was changed. Currently, oil pressure while idling is around 15psi (whereas it used to read about 28-30psi) and under load it reads about 30psi (whereas it used to read about 55psi). Outside of this issue, the car seems to run perfectly fine now. I don't know if this is due to the switch in oil, or the fact that we decided to purge a small amount of oil when we suspected the oil level may be high (we drained just under a quart or so).
I have also reset the ECU by disconnecting the negative battery terminal for around 8 min (confirmed reset by clear tripometer and "new set up" of aftermarket head unit), in hopes that it would prevent this hesitation from happening. The car seems to idle and run smoother, but the issue persists.
Does anyone have any other ideas of what could be causing this, or what else I should be checking? The oil that we drained from the car seemed to be perfectly fine (no metallic flakes or shavings).
