RESOLVED: Vibration problems after valve cover gasket replacement
 

Long story...have had my 06 4.8is for a few months. Had an oil leak at timing case cover and valve gasket so took the plunge last weekend to replace both valve cover gaskets, both timing cover gaskets and all seals/o-rings encountered along the way. Also replaced spark plugs, drive belt and leaking coolant expansion tank.

Job was a total PITA - first took 2 full days. Once we started it back up, I had a VERY bad vibration at idle, white smoke out drivers side exhaust after idle for a few minutes, much louder engine/exhaust growl and delayed throttle response on the low end. Like rattling your teeth out bad...sounded like every piece of plastic in the dash as going to shatter apart. Calmed down when you gave it gas and better at highway speeds. No codes or SES.

Figured I had a vacuum leak on the drivers side valve cover (was some oil on the back side again). So I pulled VC back off Monday to re-seat. Resulted in vibration at idle much better but still ALOT worse then before any work. Throttle was maybe better then prior to any work. Still louder at WOT then originally - but in a good way (wouldn't need that X-pipe I had previously wanted to get just a little more growl).

Unwilling to accept defeat, I pulled the drivers VC back off a THIRD f'in time today to re-seat. Results about the same = much more felt vibration at idle and low gears and louder then before I did any work. Seems fine at highway speeds. Noticed vibration is worse when I turn on the AC at idle.

99% sure I got the VC nice and tight this time (will test of oil leak once it cools down later today). Just not sure if the problem is from a vacuum leak (and where?!), plugs, drive belt, etc. I have quadruple checked all wiring/plugs and hoses.

It idled like a normal car before. I just don't know if this is normal or not. With new plugs, clean VANOS (that were crazy dirty), new belt...maybe this is the way it's supposed to feel? What/how do your 4.8/4.6is's feel and sound at idle?

I'm out of ideas and incredibly frustrated at this point having spent probably 30-40 hours dealing with it. :( Anyone have ideas or experienced something like?

Here's a video from interior (hard to hear the vibration from video...but you can tell it more when I turn on AC).

Here's a video from engine bay.

Mine is pretty smooth, it does have a little rock though, you can feel it once in a while at stop lights. No vibrations though and it sounds great.

That ticking underhood sounds very un-4.8 like. Though I must admit I don't think I've run mine with the sound insulating cover off. That just sounds really loud to be injector tick.



Mine is very smooth compared to your videos... even with engine mounts that need replacing.

Okay hate to say this but if the vehicle was running smoother before you did all this work then there is something wrong if the idle is worse and vibrations are present after doing all the work. Check to make sure no ground wires are off, coil packs seated correctly. After all that has been checked you might need to get the engined smoked to see if there are any gaskets leaking causing a small leak.

For the AC did you check the tensioner? Yes your vibrations get more pronounced when you turn on the compressor so you may have a defective tensioner. The idle of the engine looks good the engine appears to be smooth and no stumbling.

Remove the belts for power steering & a/c compressor and see if there is any improvement.

Use your iPhone to take a slow motion video of the crank pulley, A/C compressor pulley, power steering pulley and the tensonier pulley(S) - see if you can make out any wobble.

Definitely not normal; My 4.8 is insanely smooth especially considering age and miles.

Check that the spark plugs are properly torqued and the solenoids valves fully seated in the upper timing case.

+1, those solenoids are tricky. they almost "pop" back into place with a good amount of pressure.

any codes?

4.6/4.8s run smooth at normal idle RPMs. There is no cam lope at all or vibration that goes away when engine is at higher RPMs. How they sound depends on what exhaust they have. If your engine sounds different and runs worse than before you started your work stay will checking the work that you did. The premise when DIYing is there are no coincidences. If you did some work and you now have a different problem or made the problem worse--check your work. Any conclusion from the videos would only be a guess.

Have you checked for codes? Do you have a scanner that can show you real time engine info?

Still beating my head on the wall with this one. Took it to a local indy shop this week and they basically told me they have no idea what the deal is. Told me it was "over their head" and to come back and pick it up. :dunno:

Yep, we checked immediately after with a pimp Snap On scanner. No dash lights and nothing on scanner. Just had it checked at local indy shop and they confirmed no codes as well.


Ok, well good to know I guess.


This was my original suspicion. Wasn't sure I got the drivers side VC seated all the way. But local indy says it's on good and doesn't appear to be an oil leaks around it. Not sure that I believe them so may pursue smoke test again at a different shop.