P0300 / P0306 codes (misfire detected, cyl 6)

[ezMatt]

I recently purchased a 2010 Holden Commodore VE International. The check engine light was on since I bought the car, so I bought a cheap WiFi OBD-II scan tool to check the codes on the engine, and the only two that showed up were PO172 and PO175 (running rich in both banks).

Some data BEFORE MY ATTEMPTED REPAIR (at idle ,605 rpm):

• MAF: 4.78g/s
• fuel pressure: 378 kPa
• intake manifold absolute pressure: 48 kPa
• fuel economy: ~10L/100km (normal)
• car’s power felt normal

Well, I made a post here about it and someone said it could be an issue with the high pressure fuel pump leaking internally, so I tried replacing it with a used one that I ordered online, from a car the same as mine. Due to the pump being located at the back of the engine, it was a very hard for me to replace — I had to take off the entire air intake on top of the head, remove many fuel lines, etc, and accessing the actual bolts holding the pump on was a nightmare.

I also tried removing the fuel rails to make accessing the pump much easier. I did this by removing all the bolts, then trying to pry up each fuel rail with a pry bar whilst pulling on them with vice grips. However, I didn't manage to get either one out.

I don’t have a torque wrench, so when reassembling what I'd taken apart, I basically did everything up as tight as possible/what felt necessary. However, this lead to me overtightning a bolt holding the fuel rail to the head in front of cylinder 2, causing it to snap in half, but since there were 3 other bolts holding it in, I just continued reassembling the engine and decided I'd buy a new bolt later.
Well, once I'd reassembled everything, I turned the key to accessories and a bunch of warnings came up on the dash — “stability control fault”, “power reduced”, “safety mode active”. I checked the engine bay again and realised I'd forgotten to reattach the throttle body electrical connector, so turned the car off and connected it.

Then, I turned the key to accessories, no warnings this time. Then, I tried starting the car. It took a while to actually start, but now it's idling very roughly, at over 1000 RPM, 400 more than before. The engine now shakes in its mounts and vibrates badly. After around 20 seconds of running it starts making a scratchy/raspy/bad noise, and starts to die/stall after around 1 minute. I can keep it alive and running by revving it though.

After the car has been running for a minute, there is a very strong smell of petrol from the engine bay. The car also again gives me a warning saying “stability control fault” on the screen and the check engine light comes on for “misfire in cylinder 6” (P0306 reading from “OBDII”) and “misfire detected random/multiple cylinder” (P0300 reading from “ECU”).

Three things I noticed:
- the plastic intake manifold 'gasket' is quite worn and there's flaky plastic stuff on the intake manifold.
- when installing the new (used) HPFP, some very tiny fibres of heat/sound shield may have got between the gasket, pump and/or mount point.
- there's a rubber tube going from a place in the air intake tubing near the throttle body to a point on the crank case/head, the connection of this tube to the crank case is extremely loose.

Any ideas as to what's causing this?

 

[TheIceman]

if you can smell fuel turn it off before it catches fire. those rails can be a real prick, interference fit. have to get angles and position exact to get them in and out, shouldnt have to lever hard you can damage the injectors.
could be anything.