Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 11 of 11 Posts

·
Registered
2007 Trailblazer LT
Joined
·
78 Posts
Discussion Starter #1
Just had my exhaust manifold replaced on my 2007 TB and on the way home from the repair shop I stopped for fuel. Started up and it seemed a bit rough at idle. Then I backed out to head home and it cut out a couple times, sorta sputtering. Started right back up and I got home no problem. I gave it a good workout going uphill and got some black smoke from the exhaust but the truck sounds great, has way more power, and is finally quiet...

Any idea what might be happening with the rough idle and cutting out?? I know a few things get moved around under the hood when a manifold is installed; anything I should check for specifically? Perhaps some sensor is needing a smack or an air hose needs twisting? Any ideas?

Thanks
 

·
Registered
2004 gmc envoy_slt
Joined
·
2,447 Posts
This is just a guess, but maybe the throttle body needs cleaning. When they replaced the exhaust manifold, they may have disconnected the battery and this resets the PCM. If the TB was very dirty, the PCM would have adjusted parameters for that. Make sure to clean front and back sides.
 

·
Registered
2007 Trailblazer LT
Joined
·
78 Posts
Discussion Starter #3 (Edited)
I don't know if the battery was disconnected or not, but wouldn't the PCM adjust to the difference in air flow and exhaust flow anyway?
 

·
Registered
2007 Trailblazer LT
Joined
·
78 Posts
Discussion Starter #4
Should note that since fueling up after the manifold job, I've driven just 80km and burned a quarter tank. It seems like I can watch the gas gauge falling....Before the manifold I was getting about 250km for half a tank of gas.... Combined with the black smoke, minor sputtering at idle, does it sound like an o2 sensor?...It wasn't changed previously as far as I know.
 

·
Registered
2004 gmc envoy_slt
Joined
·
2,447 Posts
As far as the PCM adjusting itself, yes it will but will take a while.
If you have access to a OBDII scan tool that can show live data, take a look at the upstream O2 voltage levels. It should be cycling low and high. Also have you ever taken it back to the place that did the work?
 

·
Registered
2007 Trailblazer LT
Joined
·
78 Posts
Discussion Starter #6
I don't have a scan tool and didn't take it back to the repair place yet. I only got it back three days ago so I wanted to be sure it wasn't just a kink that needed time to work itself out. I will give it a few days and see how it goes. I don't mind the bit of rough idling but the gas guzzling is the real worry. The gas tank on a 2007 is 22 gallons or something, right?
 

·
Registered
2004 gmc envoy_slt
Joined
·
2,447 Posts
Do not wait too long to address this, since you are apparently burning too much fuel and this can lead to a clogged or damaged catalytic converter.
 

·
Registered
2007 Trailblazer LT
Joined
·
78 Posts
Discussion Starter #8
People cut those out sometimes, right? I looked online at the prices and definetely do not want to replace it. I'm gonna give it till midweek and then take it in. My calculations tell me I'm getting about 9 or 10 mpg so that is just not something to let go for long.
 

·
Registered
2003 chevy trailblazer_ltz
Joined
·
137 Posts
People cut those out sometimes, right?
The catalytic converter? Sure. If it's done by a professional, and they get caught, it's a $10,000 fine. It's illegal to sell "test pipes" that fit in place of the converter; and it would be illegal for a shop to make and install one.

If a regular consumer does it, I don't think there's a fine, but you'll never pass an emissions test; and you've created a "gross polluter".

If the shop installed a new exhaust manifold, but did not install a new O2 sensor, you need to find a different shop.

You've already waited too long to deal with this. You could already be damaging the catalyst.
 

·
Registered
2007 Trailblazer LT
Joined
·
78 Posts
Discussion Starter #10
No emissions where I live in Canada. But regardless the issue has already been fixed. I got the truck in the day after I last posted and had a new O2 sensor installed. I don't think I racked up even 100km with the failed senor in.
 

·
Registered
2003 chevy trailblazer_ltz
Joined
·
137 Posts
60 miles is enough to poison the catalyst...given the right conditions.

Hopefully, yours is still OK.
 
1 - 11 of 11 Posts
Top