New Car, New Issues

[bowtieguy]

thanks JB...i was thinking valve adjustment until i realized the car has perfect idle, burns no oil, and drives very well at lower throttle.

if it weren't for this one peace cat/manifold, id just buy a universal cat and new manifold. the valve adjustment is still in the back of my mind as reg maintenance. might have it done next tax season when i get the timing belt looked at/replaced.

[Dr. Jerryrigger]

Originally Posted by bowtieguy

thanks JB...i was thinking valve adjustment until i realized the car has perfect idle, burns no oil, and drives very well at lower throttle.

I just did a valve lash adjustment on my car. I wouldn't recommend you do it yourself, but if you have time to kill, and it's not hard to get your valve cover off, you could check the lash with out doing any adjustments.
My car was acting aright, but was clicking more than it should have been.

[benfrogg]

BTG-
How quickly do the rpms drop from open throttle to idle? I pulled my cat to seal the exhaust leak where it meets the manifold on my VX. In doing so, I flipped the cat over and over a handful of "sand" material dropped out of it. It was obviously stuck in there with no where to go.
After reassembly, the rpms didn't dive nearly as fast back to idle after closing the throttle. It was obvious I alleviated some backpressure from there. I, and perhaps you, should use a pressure gauge in the 02 hole to determine if there is backpressure there or not. (and how much)

I'd like to replace the cat myself but it isn't in the cards right now. You can also pull your 02 and take it around the block to see if this lack of pressure brings your power back instantly or not. Good poor man's test. Don't do it for long and don't do it with flammables nearby.

Let us know how you make out. I'm interested in doing this myself.
B

[bowtieguy]

Ben,

i'll have to check my rpms, but it's academic because of the crack in the manifold. i think it wise to just replace the assembly rather than just tinkering with it.

[bowtieguy]

looks like i'll be replacing the cat/manifold assembly sooner rather than later...got a trouble code P0420 today. research tells me that it is in fact the catalyst. questions...

1)should i do this RIGHT away...possibly avoiding O2 sensor issues?

i would like to avoid the OEM manifold "crack" issue, but research seems to indicate there are issues w/ after market cats in regard to trouble codes returning so...
2)should i buy after market or OEM?

[theholycow]

P0420 meant a failed cat for me when I had it, but it does warrant additional sleuthing before you implicate the cat...it could mean almost anything that results in improper exhaust content or an improper measurement thereof. Guesses of additional possibilities: Pre-cat or post-cat O2 sensor worn out or mispositioned, leak between pre-cat O2 and post-cat O2 (whether in pipe or cat), etc.

A quick googling also suggests engine coolant temperature sensor malfunction or retarded spark timing, though I'm not sure how those could cause it.

[bowtieguy]

thanks HC.

considering i DO have an exhaust leak via the manifold crack, it likely is the cat. besides, the upstream O2 sensor is new, so...

[VetteOwner]

yea that crack prolly told theO2 to dump in more fuel which usually kills cats and O2's, it COULD be the downstream O2 gone bad which i know on GM is purely there to let you know if the cat is bad or not, it could have gotten buggered up with overfueling too.

id fix/replace that cracked manifold before you do anything.

i know the 2.2L GM engine needs some back pressure as do most engines but not crazy ammounts and it will cause stumbiling and poor accel at high RPM's (when exhaust gasses are trying to flow the fastest) if its got too much IE restriction

[palemelanesian]

Since the manifold and cat are one piece, I'd go ahead and replace it. Kill 2 birds with 1 stone. I'd use an aftermarket part. Cheaper and possibly less likely to develop the same crack. That's what I plan to do when mine opens up.

[bowtieguy]

one more question before i buy...

dorman makes a 2 piece, keeping the cat separate from the manifold before install
atp makes a 1 piece assembly

so, here are my thoughts...
the one piece is more like OEM, and i could see fewer issues w/ say leaks and subsequent O2 codes
the 2 piece would seem less likely to have the manifold crack again

your thoughts?