96Formula6spd

Hey everyone. I picked up a new to me 2003 350z the other week. Plans are to make it into a spec 350z race car. Bought the car with it not running very well and leaking a lot of oil. Its got its problems but the body is straight enough and the interior is just bad enough for it to become a good race car donor. Anyways when I got it I found the valve covers to be leaking oil where the gasket was pinched. I also found many intake manifold leaks. Car has a plenum spacer and it was missing a total of eight bolts.

Step one was fixing the intake leaks and valve cover leaks. Fixed those and got the car running much better with a brand new set of NGK plugs as well. Car seemed happy. I only changed the upper and middle intake gaskets. All were blown. I left the ones on heads alone. Car was running good so I decided to load it on the trailer to take it to a place where I could drive it. Car is not street registered. Well the bolts backed themselves out and I blew the intake gaskets. I did another set of gaskets and some blue loctite. So far so good with intake leaks. Still have not touched the intake gaskets on the cylinder head, more on this later. Figured the car was throwing some oxygen sensor codes. So I ordered new ones and got them installed. Car runs better but the miss still comes and goes. Going to list what all has got changed down below.

- Plenum Gaskets. With a new throttle body gasket. Ones on cylinder head have not been replaced.
- All PCV hoses where changed due to everyone being cracked.
- New NGK spark plugs. Iridium units.
- Six new Denso Coils (Thought one had failed so just got six.)
- Fixed Camshaft Bank one Sensor connector as it was broken.
- Replaced all Cam and Crank sensors with Hitachi units. Had a P0340 code.
- Brand new NTK Oxygen sensors. Did all four as two out of four where throwing odd ball readings. Two were throwing codes for heater circuits.
- Fixed coil back connectors on cylinder 1/3 with a used harness. Old ones locks were all broken.
- Done throttle body relearn. Both by pedal dance and scan tool.
- Cleaned the mass air flow. Was very dirty. Also swapped with a used one from a know good car. Both run the same.
- Checked and cleaned all grounds in engine bay and interior. Nothing loose or dirty.

So this is where I am at. I can fire the car up and sometimes its fine. But you go to take off and the misfire will come and go. Car seems to pull fine one minute then flat on its face another. Decided tonight to check compression. With my old gauge these were the readings. Making sure I did not have a dead or weak cylinder. I did budget an engine on this car. But then one seems happy enough to play with it first.

#1 - 180psi
#2 - 182psi
#3 - 185psi
#4 - 183psi
#5 - 182psi
#6 - 183psi

So engine seems good. Nothing there that says we have a problem. Cylinder one is the worse but only 5psi lower than the rest. Now when I did this the plugs all looked good minus cylinder one. It was soaked in gas. You can see below.

Cylinder one on left. Cylinder three right. Rest of the plugs match cylinder three.





Whole Set



So right now this has me a little stumped. Here is an idle video of the car from today. Just does not sound right. Maybe I am wrong?


This video also shows the ticking sound that usually comes with the misfire. However it was not at this time.


Have a couple other videos but the sound is not good enough to hear on them.

So anybody got any ideas. I think I am going to start tomorrow by doing the lower intake manifold gaskets. I will also maybe move number one injector around to cylinder two as well as replace the o-rings. Figure if its a trouble maker and maybe a sticking injector the problem would move unless its a wiring issue. Figure what ever issues I have is with cylinder one. The ticking sound is coming from that area when it shows up with the misfire and the plug is way worse for wear vs the other five. Anything else to check for while I am in that deep?

SlowZ333

I’m interested in what people say because I just bought an 03 and am having the same problem except I just have P0300 multiple misfires. I changed spark plugs and that didn’t fix it. I read some forums on here from a long time ago and it seems to always be a coil pack so that’s my next move.

96Formula6spd

Well it seems I found the issue. When I took the car apart the first time there were only five bolts under the intake manifold. Well i figured since they did not put seven on the outside what is one more. Well I pulled the intake manifold back and out and found this little surprise the missing lower plenum bolt....

Look what I found.



That is not the worst part. Its where I found it...



Can't believe I did not see this guy the two times I pulled the intake. Granted I had thought the guy just not put it in. I changed the lower intake gaskets and moved the injector to confirm. But looks like my ticking sound was the bolt smacking the valve. Valve looks ok. Car is leaking some oil so I think over the winter the engine is coming out and the head will come and get a new valve and I will do a good reseal before it sees a lot of track time. Did take the car around the block and it pulls fine and is not making any bad sounds. No codes on the computer as well. So looks like we are in the clear for now at least.

iideadeyeii

iTrader: (6)

Holy shiz, haha. I was going to say stuck injector from the plugs, but then I saw the last pic