Exphiliac

I've got a 2003 touring just hit 100k miles that has an intake, plenum, and catback exhaust on it. Ever since I bought the car, I've noticed that after hard turns and stops my oil pressure drops and rises again slowly, usually about 30 psi each time. I did some research and I guess this is normal because of oil surge, but I also noticed that over time my oil pressure just ttends to drop in general. When I do a fresh oil change the pressure shoots to around 90psi on cold start and stays around 60psi at idle for a while(a couple weeks).
Currently, the pressure shoots to around 60 on a cold start and stays around 30 at idle. So with the surge problem my pressure tends to drop to 0 and hit the warning light on normal turns and slightly hard braking. It's only been a few weeks since my last oil change(less than 1000 miles). So my oil is losing it's viscosity at a pretty quick rate. Oil level seems normal and I'm using full synthetic every change so I'm stumped.
I'm thinking that there's fuel getting into my oil somehow and breaking it down because I can smell it on the dipstick but I can't find where they're mixing. Ive already replaced all my injectors but I haven't replaced my pressure sending unit if that means anything. I could use some help with what could possibly be causing my viscosity to be dropping so much so fast. I mean I can start it all over again and just change my oil but I've already gone through 4 oil changes in 6 months...

rancor

I haven't heard of oil starvation issues with the Z before. If you are racing the car on slicks maybe, I think i remember a 370Z killing his VVEL from oil starvation but that seems to be a rare case. Is the engine clean, or filled with sludge? Maybe if the oil is getting stuck in the heads it could be causing a problem?

If you can smell the gas in the oil that is probably the cause of your oil dilution. Have you seen any other issues? Check engine lights, misfires, is your car badly tuned, running very rich?

About the best I can give you is this. It might be worth checking compression.
https://www.amsoil.com/techservicesb...20Dilution.pdf

Exphiliac

It's a daily driver, I've never taken it to the track. The engine is clean- I've ran seafoam and other cleaners through it a couple times. I do get an occasional random misfire code but it usually goes away immediately. The car was running very rich when I first bought it but it was also straight piped. I have since put catalytic converters on it and they helped reduce the fuel consumption.
It used to smell pretty rich before I put the cats on but now it only really smells if I gas it hard and have the windows down. I can look into a compression test and I'm actually not sure how well the car is tuned. I've got a new pressure sending unit and vvt solenoid on the way and I'm gonna see if replacing those helps any. Anything else I can do?

rancor

Then you shouldn't be getting oil starvation issues unless something is wrong with your oil system, but I have no idea what. What does the camshaft look like if you open the oil fill cap? Do you still have the OE oil pan?

On to the misfire, if you are having one something is wrong and this is probably the place to start. Is your engine throwing codes, have you checked it with a code reader to see if anything is stored? It might help to know what cylinder is misfiring. Have you pulled the plugs to see if they need to be replaced or are fouled? One issue might be the spark plug tube seals. They are known to leak and can cause a misfire.

If you remove the spark plugs please post pictures. The gas smell on acceleration is odd considering the exhaust is behind the driver. Have you checked your PCV system to make sure it is hooked up and the valve is working?

The gas smell with test pipes isn't necessarily a sign of running rich, just that your catalytic converter used to take care of that. Test pipes actually tend to make these cars run lean on the stock tune. Try and fix the misfire first the oil problem and gas smell might be related.

Exphiliac

Camshaft looks clean as far as I can tell and the oil pan is OE. And the misfire code happens maybe once a month before going away immediately so I'm not sure what it is. Every time I use a code reader on the light it'll show p0300 random multiple misfire rather than narrow down a cylinder. The only other code I've gotten was a bank 1 running lean code that appeared once along with a p0300 code but that's it.

An autozone reader came up with a suggested replacement for the bank 1 vvt solenoid with that bank 1 running lean code and I've got one of those on the way. I also replaced all my spark plugs with ngk ones back in November along with my coil packs a couple months ago. When I took out the old ones cylinder 4 and 6 plugs were wet and a couple others were white so I suspected valve seals. A vacuum test determined that was not the cause.

I've messed with my pcv system in the past because it was drawing oil into the intake right around the time I did the spark plugs so that may have caused the wetness. But I've since installed a catch can on the driver side hose and I know for sure the passenger side one is completely connected(also with a new pcv valve as of December) so there's no venting.

I do know for sure that the p0300 code will happen if I take a long trip such as 3+ hours and when that happens it doesn't go away until I reset the ecu or clean the maf. I've also completely sealed up around my plenum with rtv to ward off vacuum leaks and put a brand new throttle in about a month and a half ago. I mean, there's only so many parts I can replace before I get the correct one, right?

It's also probably worth mentioning that if I add more oil the pressure goes back to normal for a couple days then goes right back to where it was before.

Exphiliac

Update:
I replaced a few different parts a couple days ago and here's how it changed. While I was doing my oil change I also put in a new pressure sending unit(not oem). I also put a new driver side vvt solenoid on and did a pcv delete to eliminate oil consumption. With my pcv delete I put a breather on a drilled out pcv valve and a catch can on the opposite side hose to maintain vacuum from one side. I also refilled with Mobil 1 extended 5w-20 (4 1/2 quarts).
Right off the bat the new sensor read drastically different from the original one. At idle it sits at just a hair away from zero without illuminating the low oil pressure light and doesn't go above 50 psi even if I rev it high. So now I'm thinking it's either another bad pressure sensor or it's the pump.
The pressure still drops when I turn and brake but not nearly as bad and goes right back down to near zero when I'm not in gear.
I ordered an oem pressure sending unit and I will post another update as soon as I get some data from it. I'm also going to end this with a couple of questions:
- I noticed that the original sending unit wasn't screwed completely in, so does that mean I have to have a new sending unit be screwed in a certain amount of turns?
- does a brand new sensor require a break in period? I've had this one in for a few days now and there haven't been any changes in its behavior
-how difficult and time consuming is an oil pump replacement?

rancor

Why are you using 5W-20, the car is designed for 5W-30 a 20 weight will be to thin and is probably why your oil pressure is low.

The oil sensor threads are tapered the sensor only needs to go in about as far as the original. If you try to screw it in further you might crack the block/upper oil pan.

Pretty sure the oil pump replacement requires dropping the upper oil pan, not an easy job.

Exphiliac

That's a very good question. I'm not sure how I managed to grab the wrong grade considering how many changes I've done alreadyand that is the first time this has happened. You sir are a gentleman and a scholar. I'll post another update once I get the right oil in there.

NissanTracker

iTrader: (8)

I just updated my oil pressure issue here:

https://my350z.com/forum/maintenance...iast-151k.html

and here:

https://my350z.com/forum/maintenance...-pressure.html