General Maintenance & Repairs - Misfire then tap/knock sound/pcv disconnected (long)

Spirited driving on an hour long road trip, on the way back the service engine soon light began to flash. Code p0308: Cylinder 8 misfire. (Didn't know which cyl until I was able to get home, if i kept revs at 1500 or below it didn't seem to misfire enough to trigger a CEL or at all maybe)

So I pull over, since it was throwing a misfire all visible wiring, spark plug wires (except for 8 I couldn't reach it from the top) all I could see seemed fine. Checked engine oil, level is fine, checked trans fluid, level is fine, checked flexplate bolts, they are perfect. I'm sure the engine would have been shaking but I have solid motor mounts so she wasn't budging.

I get home and hook it up to the scanner (I have a tech force 2) and read the codes and datastream information from the vehicle. p0308 and there has been a lot of misfire count (over 5600) in the history on cylinder 8.

I jack up the car and access the #8 plug wire from the bottom... loose. I snug it back on there sit her back down and try to snug the top of the wire by the coil. I notice a little bit of oil around the area. I glance to the right and I see the PCV nipple coming off the valve cover is not connected. The hose came off and is laying beside it. I reconnect that and fire her up.

All seems well, no crazy sounds and the engine is running normally. I connect the Tech Force 2 scanner back up and go for a drive. Misfired once in about 10 minutes. Everything felt strong so I took it to redline... running perfect. I get back to the house thinking I may have dodged a catastrophic failure and then as its sitting there idling for a minute... I hear what sounds like something tapping in a single cylinder. Key off, time to go to work... called a cab.


The tapping at idle (seems to go away if at anything over idle) seems to change in intensity. it will be quieter, then louder, then quieter... a single hit each time. The question is... what is hitting where? :huh:

2000 T/A stock longblock, stalled A4, 116k

Going to take the valve cover off for a little self inspection. Anything else you guys recommend?

I don't know if LS1's have coil packs (the LT1 has an opti, what's the LS1 have?) but if it does, make sure they are working properly (search for how to test them). Also, how do the spark plugs look? I think the LS1 has a distributor -- make sure that's working. I don't know much about the LT1/LS1, since I never had my head under one, but I know a lot about my 3.8L :D

The tapping might be an exhaust leak too... I think the LS1's are notorious for ticking noises.

lifter/cam wear? how often do you clean your throttle body and upper engine?

did you check the plug on #8? could be fouling out. if you have a tapping noise, check your rockers and make sure a rocker bolt didnt back out.

also, if your plug is new, or you put a new one in and it still misfires, take that spark plug wire off and move it to a different cylinder. run it and see if the misfire follows your wire. you will know if its the plug wire or not.

just some suggestions

I popped off the valve cover and everything looks as it should and surprisingly clean.

I eliminated the misfire in my first round of troubleshooting when I got home. (loose plug wire on cylinder 8, techforce2 scanner basicallly hasnt shown a misfire since, and no more flashing service vehicle soon light)

I havent cleaned the upper engine, but I cleaned the throttle body very well (off the motor) and it is still as clean as the day i reinstalled it months ago. (I have egr deleted) It might be that clean because the pcv hose from the drivers side head to the passenger side head was disconnected for some reason (overlooked during reassembly perhaps)

Plugs have about 4,000 miles on them. The car does not have any power loss since the plug wire was reseated. Pulls to redline without a hiccup.

All of this is leading me to the lifter... Oil pressure has never been an issue in the past, at cold idle its 40-45 psi and hot idle is about 25 psi.

Could the spark plug wire getting loose and a misfire cause damage to a lifter?

I have a full bottle of Marvel Mystery Oil and I hear it can help with freeing a lifter (if thats whats going on?... we'll see)

Going to dump it in probably tomorrow and drive around easily for 15-20 minutes and see what happens... Maybe it will explode and I can start a LQ9 build... who knows.

Well I tried the MMO and it seemed to help a little at first but in the end it didnt. I'm thinking the lifter possibly rotated. In storage she goes.