Park Avenue Elusive Engine Noise/Problem

[Knot Waiting]

2002 Buick Park Avenue Ultra (supercharged 3.8l L67 V6)

This may be a little long but its the whole story and its got me beat. Thanks in advance for any advice.

For the last few months my engine had been making a slight lifter noise at start up. It didnt allways happen and it usually went away in a few minutes after they had a chance to pump up. I was waiting for warmer weather to address the issue.

Then the problem began to get worse. On hard acceleration the engine would stumble, bog, and the MIL light would come on. One night of foolish driving the light began to flash and the engine shut down. It restarted right away but there was a heavy tapping sound from the rear (right) of the engine and it could barely maintain idle. A scan tool pulled code 3004: #4 cylinder miss-fire.

I pulled the spark plug and found it had burnt up, no electrode or prong. Replaced it and the engine ran a little better but the MIL light still flashed and there was still a loud tapping sound from the lower end on #4. Compression check showed the noisy and misfiring cylinder was 50psi low. I tore the engine down and replaced all the valve lifters (roller type pushrod single cam). No damage was noted to the valve train, although I didnt remove the head. Reassembled, torqued to spec and had very little change. Check engine light went out and the misfire cleared up mostly.

Now the engine makes a loud "clack, clack, clack" noise that increases with RPMS. The strange part is that it fades from noise to total silence every minute or so... ??? I cant figure it. No MIL light, almost no misfire, low compression and consistant a fade in and out noise.? Still sounds like its comming from the #4 cylinder low somewhere. Any ideas? Maybe Im just frustrated but nothing makes sense. Thanks.

P.S. The noise is ever present while accelerating and driving at speed. Only parked and idling does the loud noise fade in and out.

 

[Bondo]

Re: Park Avenue Elusive Engine Noise/Problem

Ayuh,....

You might find this interesting,....

 

[Bob_VT]

Re: Park Avenue Elusive Engine Noise/Problem

1st it's going to require surgery

The good news is that the 3800 is a common engine and if any transplanting is needed ....... hit a junk yard.

I have seen the 3800 break rings and put rods through the block too.

 

[xtraham]

Re: Park Avenue Elusive Engine Noise/Problem

those engines or notorious for the harmonic balancer going bad and making a noise not unlike a bearing knock, I'd check that first

 

[projecthog]

Re: Park Avenue Elusive Engine Noise/Problem

Sounds like a bent intake valve,
Not an exhaust valve, because the engine doesn't make popping sounds(right?)

If so, the plug burned because of Oxygen rich combustion (lean mixture) melting the electrode off the plug over time and removing the bridge on it.

The valve could have been bent in the process of the plug losing the bridge, starting the sound you hear. You couldn't have checked for that because you didnt have the head off.
The whole reason I mention the bent valve is because of the sound you describe but it doesn't nessessarily have to be bent.

I exclude bad carb settings or timing as that would likely have affected all the plugs at the same time.
It could have started with a leaking head gasket, or anything related to air coming into the cylinder when it shouldn't. Not likely a bent intake valve as a cause, but rather as a result, but who knows?
A Headgasket, maybe a leaky intake manifold or.....,rocket fuel.

Ask yourself if the engine ever overheated or boiled over or did it ever freeze?. Does it use small amounts of water at times? Does water (coolant) disappear without a reason?
Is there bubbles showing in the rad fill neck or rad overflow can?
All of these can indicate a leaking headgasket or worse.

There can be more reasons for the noises you hear, it could range from broken valvetrain parts to bad sleeve bearings, to loose mains, although the last two do not line up with the symptoms a whole lot, especially the burnt plug.

The reason I addressed the bent valve or bad headgasket/intake gasket idea, is because that seems the most likely thing to me, if it is anything else, it gets too involved to explain for a long winded feller like me, who is just guessing at it anyway.
You may be looking at some serious dollar spending if I am wrong, or it could be a simple thing I didn't think of.(Murphy! yeah.)

Good luck with it, take care,
PH.