Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 12 of 12 Posts

·
Registered
2002 chevy
Joined
·
2,582 Posts
Discussion Starter #1
A month ago Ive got headers install which was great btw, everything seemed fine except getting the engine code P0420 which was the high flow cats. I got it removed from the tune but the light still pops out.

But that's not the problem. A month later Im starting to hear knocking noise for the first time when at 70mph. Anything where before or after 70mph I don't hear any knocking noise. The truck feels like it had lost some power around 1-2 shift and my gas mileage decrease from 15 to 13.2. And sometimes when at stop or park the truck revs automaticly for no reason several times.

Ive looked at previous threads and have not found answer. I would appreicate some advice from the experts on this site. Thanks

Heres what I got replaced a year ago:
1) All spark plugs
2) Ignition Coils
3) Both O2 sensors
4) Clean throttle body
5) changed air fliter
6) Oil Change (sythetic)
7) Battery
8) Alternator
9) Ignition switch

misfire.jpg
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
4,125 Posts
Where is the knocking? Do you hear it or feel it? Coasting or on the gas make a difference?

Could your 2WD parts that you added have come loose?

(Your front diff is doing awesome BTW. Been rippin some crazy donuts with it)
 

·
Registered
2002 chevy
Joined
·
2,582 Posts
Discussion Starter #4 (Edited)
Where is the knocking? Do you hear it or feel it? Coasting or on the gas make a difference?

Could your 2WD parts that you added have come loose?

(Your front diff is doing awesome BTW. Been rippin some crazy donuts with it)
Of course! I keep my stuff in peak top shape! :D

The engine knocks sound like train tracks. I hear the knock on the engine side while coasting at 70 mph in the hwy and felt a lost in some power around low throttle. Its as if the engine got leaner.

Btw i did the mod for the oxygen sensor and it still pops up. When I did a dyno the rear oxygen sensor has no voltage reading on the dyno even though the rear and front o2 were already replaced.


Hhmmm Luis, where is your rear o2 located on the end of the headers pipe? When looking straight ahead the engine is in front of you, my sensor is on the left side of the pipe near the exhaust pipe. Kinda close to the bottom frame pointing toward the trans. Is your sensor near the same location as mine?

 

·
Registered
2002 chevy trailblazer_ls
Joined
·
4,125 Posts
You might have to add the second spacer but do not drill it. Just put that one in the pipe then the drilled one after that one. It just hit me that you got the Y piped headers and all 6 cylinders go thru the one cat. I have true duals so each of my cats get fed 3 cylinders. My rear O2 is somewhere by the rear of the trans so just like your pic.



As for the knock, I had one that knocked only when the A/C was off. It turned out to be the A/C clutch bearing.

http://forums.trailvoy.com/showthread.php?t=53918

You could try a shorter belt mentioned in that thread and see if it's still there. Could also be an idler pulley.
 

·
Registered
2002 chevy
Joined
·
2,582 Posts
Discussion Starter #6
As for the knock, I had one that knocked only when the A/C was off. It turned out to be the A/C clutch bearing.

http://forums.trailvoy.com/showthread.php?t=53918

You could try a shorter belt mentioned in that thread and see if it's still there. Could also be an idler pulley.
The idler pulley was already replace BUT when i replaced the alternator with a 250 the pulley was a lot smaller than the stock. They said to get a smaller belt but I couldn't find a smaller belt until your mention it on the thread above.

Thanks Luis! Ill try replacing the bearing and getting a smaller belt. Was this the right size (705K6) belt you got Luis???
http://cgi.ebay.ca/705K6-belt-KELLY-NOS-GM-FORD-MITS-etc_W0QQitemZ350303206107QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item518fb2badb
 

·
Registered
2002 chevy
Joined
·
2,582 Posts
Discussion Starter #8
my shorter belt was for no A/C w/ stock everything else.

If your pulley is smaller I would say the 705k6 is too small to use w/ A/C
Alright, i get the ac bearing replaced and see if it stops the knocking noise. Thanks!
 

·
Registered
2002 chevy
Joined
·
2,582 Posts
Discussion Starter #10
I would try a shorter belt first cause it's less espensive and you can get it at any parts store today. The bearing is special order and it's a lot of work.
I just dont get how the headers play a role in this ac bearing problem...
 

·
Registered
2005 chevy trailblazer_ls
Joined
·
422 Posts
Well for the revving when stopped I'm pretty sure that's because of the loss of backpressure you have with your headers? I'm not sure what kind of flow these headers are supposed to give you but I do know that ever since I cut off my res. and muffler, my TB has been doing the same thing... :m2:
 
1 - 12 of 12 Posts
Top