Good evening!

I got my 350 a little while ago upon looking over the engine I noticed valve covers seemed to be leaking along with some plenum gasket leaks.
I went to go do all new valve cover gaskets and upon pulling the spark plugs noticed cylinder 4,6 and 3 had oil in the spark plug tubes. I figured since I’m here might as well do some aluminum valve covers. New iridium NGK plugs and clean the coil pack boots etc. I took the fuel rail off checked the fuel injectors nothing was cracked or damaged, I did keep stock ones in there just as they are expensive and already running a fairly tight budget.
put everything back together double and triple checked everything before starting.
when I did start it I let it fully warm up and noticed I’m getting a little bit of faint white smoke coming from the rear left side of the engine bay (passenger side) and still getting a P0304 and P0300 codes, (cylinder 4 misfire) and (random multiple misfire) as well as a P0327 (knock sensor 1 circuit low bank 1).

If anyone has any ideas on what to check next on why it would be misfiring or how to diagnose specifically why it’s misfiring let me know!
my ideas right now are get new coil packs and MAYBE new injectors. I tried some Techron with new 93 about 5 gallons and tried to let it idle for a while see if that helped clean the injectors further and still no change.

 

I have changed ignition coils, it seems to be an injector problem? That’s my only guess. I’m going to do a compression test and if everything is good there swap injectors from cylinders 2 and 4 and see if I misfire cylinder 2 instead then I know it’s for sure injector issues. If anyone has any other suggestions that would be helpful!

 

Were you getting the misfire codes before you did the valve cover job and messed with the injectors?

It's very possible that by disturbing the injectors you could have introduced a fuel leak. Those injector seals are delicate and once disturbed should really be replaced, especially given the age of these vehicles. When you re-installed the injectors, did you lubricate them with some silicone? If not, it's possible that a seal ripped or tore.

There are some known issues with the VQ35DE knock sensor sub-harness. It's rare for the sensor itself to fail, but better safe than sorry when you have to remove the entire upper and lower intake to gain access. It's also possible that while doing the valve cover job you disturbed the knock sensor wiring. Best to replace both, you can get them from multiple sources. Here's just one example.

Good Luck!
-Icer

 

And, double check wiring to coils 2 and 4. Easy to inadvertently switch them resulting in a P030x DTC. Sounds rudimentary but many an experienced wrench has made this error as they're really easy to mix up.

Oh, certainly not me!! I don't make mistakes like that.

i reserve my blunders for other automotive sub-systems. 🤡

Laff....

 

YES, what MIC said!