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2006 chevy trailblazer_ss_3ss
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17 Posts
Discussion Starter #1
I wanted to post a driveability symptom with result...just in case there are others working through this issue.

I recently had some driveability issues. Generally, loss of power. According to the data logger, the engine wasn't able to deliver more than 220 ft-lb without picking up knock. I was also picking up engine codes for missfires on 5 & 7. When i looked at my data logging, I found the driver side bank to be reading way lean and there were consistent missfires throughout that bank (1-3-5-7).

I found a broken drivers side converter was blocking exhaust flow of that bank. See the pics of the good vs bad. I'm not certain, but the cause may have been my +10% fuel during power enrichment and an extened run at 130+ mph and shutting it down right after. I think the converter was overheated and then allow to cool to quickly...causing the crack and allowing the substrate-to-outer case cushioning material to fall in front and block the converter.

I've eliminated the blockage, and I have my power back. :woohoo:
 

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2004 gmc envoy_slt_xuv
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Loss of engine power

Hi, This is my first time to post in this forum. I am a new member.

I'm having intermittent problem with my Envoy XUV sometimes it looses driving power and seldom run normal engine power. I replace fuel filter, air filter, cleaned the throttle body, spark plugs, change engine oil, transmission oil, and differential oil. Problem still exist.

I brought it to the car shop and the mechanic run computerize diagnostic test but failed to detect any problem. Need help.
 

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2002 olds bravada
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2,369 Posts
wow 3 years old and already a bad cat? i wonder why so soon..:undecided

Hi, This is my first time to post in this forum. I am a new member.

I'm having intermittent problem with my Envoy XUV sometimes it looses driving power and seldom run normal engine power. I replace fuel filter, air filter, cleaned the throttle body, spark plugs, change engine oil, transmission oil, and differential oil. Problem still exist.

I brought it to the car shop and the mechanic run computerize diagnostic test but failed to detect any problem. Need help.
If you feel like performance bogs down and notice a "rotten-egg" smell its most likely a bad cat. It can also be a bad o2 sensor as well. Best way to check is to use a scan tool and read the voltages to the sensor
 

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2004 gmc envoy_slt_xuv
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Loss of Power

If in case the CAT is clogged and because it's difficult to find replacement here in Saudi Arabia, will it be ok if I bypass the CAT but keeping the O2 sensor? It's no problem here driving without the CAT. Will there be louder exhaust even during idle?

Regarding O2 what is the normal voltage reading on the scanner? Here, the mechanic does not tell us what's he getting from the scanner, he merely says "no problem" or "problem".

Thanks for your advice. I'll update soon.
 

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2006 chevy trailblazer_ss_3ss
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17 Posts
Discussion Starter #6
The failure occurred at 52k miles. So, in most circumstances, that failure would be covered by the 8yr 80k warranty required for all emissions related components here in the United States.

When I had this failure...it was an immediate loss of power, not intermitent in any way. I never got the P0420 style "catalyst inefficiency" code...that surprised me given the level of blockage. The engine missfires and excessive fuel trim were the only things I saw during data logging. If you can't get "full power", I would add the catalytic converter(s) to the list of items to suspect. Given what you've already done, I would recommend checking the fuel pressure (I thing it's supposed to be 58psig) first. If that checks out fine, I would turn to the converters. It's no easy job removing the converter assembly...several other components need to be removed to get it out. I ended up cutting mine apart. If you are looking for the quickest way, I say cut in front of both converters and pull the pipe down far enough to look at the substrate (mesh, honeycomb, etc). If it looks good, you only have two spots to weld back in place. If it looks bad, you have two more cut and some straight sections of pipe to weld in place.

In my case, I did not think it to be ethical to turn this in for warranty since I was adding extra fuel during Power Enrichment and running above the 130mph factory speed limiter. I think the extra fuel overheated the converter. Unless I start hearing about lots of failures of "stock" vehicles, I wouldn't worry.

The voltage on the O2 is not constant. It swiches between a lower and upper voltage many times each second. Typically the voltage will bounce between 100 millivolts and 900 millivolts during operation. That switching is used to trim fueling levels up or down...which is seen while data logging the Short Term Bank fueling levels. If the trim levels are exceeded, it should set an engine code.

If the converters are removed, there will be engine codes set for the secondary oxygen sensors. You can retune the computer to eliminate the codes or get some MIL eliminators to simulate the sensors. The sound level does increase, not bad but I'm not sure what to compare it to. It's definitely louder than the stock SS and there is some resonation within the stock muffler during high rpm operation.

Good Luck with the diagnosis.
 

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2007 chevy trailblazer_ss_3ss
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208 Posts
Common in tunes to turn off the COT enrichment or mess with those numbers. Maybe you had this turned off?
 

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2004 gmc envoy_slt_xuv
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loss of power: update

Hi guys, sorry for the delayed update. I brought my car to the carshop and they did PCM program upgrade/update (some sort of calibrations as what i've seen). It run ok now but it's now under observation. My mechanic expects me to come back to him tomorrow for any comment.
 

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2006 chevy trailblazer_ss_3ss
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Discussion Starter #9
Common in tunes to turn off the COT enrichment or mess with those numbers. Maybe you had this turned off?
I didn't change the Catalytic Over Temperature protection values. The COT was "enabled" and the temperature thresholds were the stock values (1787, 1697, 1661 deg F in the three different ). I just made the tune WAY too rich...and cooled it off WAY too fast.

I should've spent some money on a wide band O2...but instead I had to spend money on exhaust parts. :duh:
 

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2004 gmc envoy_slt_xuv
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SOLVED: Intermittent Loss of Engine Power

My Envoy XUV 2004 has 84K mileage.

The mechanics actually did not fix my problem, he insisted that the fuel pump is the culprit (intermittent engine power loss). Here's what I did:

Replaced the following parts (did not fix the problem):
-Accelerator Position Pedal
-Camshaft Position Actuator Solenoid (due to oil leaks).
-Catalytic Converter (found partially clogged)
-Oxygen sensors
-Intake Air Temperature sensor

The fix:

Replaced Fan Clutch (even it appears to be good and rotation-tested), and that's it, back to normal engine power.
 

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2002 olds bravada
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Even with out the GMPP, you're covered under a federal warranty up to 8 years or 80k miles
 
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