newly purchased '04 CVPI...and now there's noises....help...

[ltdcrwnvic]

hey guys....

my buddy just bought a '04 p71 PI and after a few days of driving it, it started making some noises underneath the car. we didn't hear anything when we test drove it until now. we will inspect it later today but here is what he has been noticing:
-sound appears to be coming from under the car, by the tranny or behind the engine somewhere
-you can only hear the sound when the car is idling and at times after you let go of the gas when driving
-while driving, the sound disappears
-while at low rpms, it kinda sounds like the typical tin can with marbles in it.

what do you guys think it is? we're hoping its a possible bad/loose cat, bad/loose muffler/exhaust pipe, or something loose overall, or is it the timing?

thanks for any help.

[gadget73]

sounds like a broken exhaust hanger, or a cat converter heat shield broken loose. Probably should be fairly easy to find if you get under it. Shake things around, something will make a funny noise.

[Ryan12689]

Don't know if this will help, but my 2004 P71 has bad rot and rust on both exhaust manifolds, all over. Maybe the flanges on the manifold is rusted away and became loose?

[ltdcrwnvic]

well guys......we drove the PI onto some ramps and fired it up.....we found out where the knocking was coming from. it was the drive side cats....we thought it might have been the heat shields but even after we compressed em and held em tight, the knocking was still present inside the driver side cats, the lower one specifically.

my buddy was thinking of just buying the whole part brand new off ebay since he's afraid if we gut 'em, the O2 sensors might make the check engine light turn on. he was also thinking of just going straight pipe, no cats, and 2 mufflers, but then again the thought of the check engine light turning on lurks in his head. if he does buy it, besides taking off the 4 bolts and the O2 sensor, that else is there to worry about?

should he replace both sides(all 4 cats)? straight pipe? gut the cats? what do you guys recommend?

[marquisman]

The cats are pretty much needed, since you got a set of O2s after the cat. The ECM will have a hard time tuning the air/fuel mixture, if both O2s in one bank have the same reading. I would go with a set of magnaflow direct replacement cats.

[sly]

it won't jack with the ECM, but it'll throw codes all day long telling you that the cats are screwed. the engine will still run fine without cats. and since it will light the CEL, if you have inspection nazis/emissions, it won't pass.

[gadget73]

if its got less than 100k on it, I believe those parts are all warranted for 10 years and 100k miles. I don;t know if they will replace them on fleet vehicles or for noise problems though but its worth asking about before actually spending money.