Engine Power Loss

Tiny
DELGADODANIEL
  • MEMBER
  • 2007 GMC SIERRA
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 111,900 MILES
I have the check engine light on and so far all the shops I have been to say its a catalytic converter issue, at least that is what the code reader says. It shows as both banks being bad also the most recent shop I went to said due to the bad catalytic converter. I also have one cylinder misfire. Well since I cannot afford to fully fix it all right now I have been driving it as it is. But now every time I have to rev up the engine a little to get up a steep hill I have no power and I am stuck between 3000 rpm's and 3500 rpm's.

The engine has a hard time switching gears and not sure why this comes up but on my dash the "check engine light starts flashing, the stability track is off, then traction control is off and after it says to service both of those. I am hoping that once I do change the catalytic converter this whole issue goes away. But what else would you suggest the issue is? Please Help I do not want to get rid of my truck.
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Thursday, September 15th, 2016 AT 1:22 PM

3 Replies

Tiny
CJ MEDEVAC
  • EXPERT
Sort of sounds like maybe a big ole chunk of the catalytic converter innards may have broke loose and is now blocking the outlet. The catalyst sort oc looks like a honey comb (allowing exhaust to pass through) but its kind of brittle like charcoal. A loose chunk turned sideways is almost like crimping your exhaust pipe off.

Might not be a good idea to drive it like that. The excessive heat and the back pressure is not your friend or your trucks. Then there is the safety factor whereas you might not be able to get out of a jam quickly.

The Medic
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Thursday, September 15th, 2016 AT 7:46 PM
Tiny
DELGADODANIEL
  • MEMBER
Would it help to clean it out or just simply replace?
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Friday, September 16th, 2016 AT 7:23 AM
Tiny
CARADIODOC
  • EXPERT
Hi guys. Excuse me for butting in.

You are doing yourself a disservice. By not fixing the problem properly, it is going to cost you a lot more very quickly. The clue here is the flashing Check Engine light. First the Check Engine light told you the Engine Computer detected a problem, and that would be related to the misfire. A spark-related misfire sends unburned gas and oxygen into the exhaust system where the oxygen sensor detects that oxygen as a "lean" condition. In response, the computer adds more fuel to the fuel metering calculations, but it adds it to all the cylinders. Now you still have the unburned fuel from the misfiring cylinder, and the additional fuel from the other cylinders, that all gets burned in the catalytic converter, PLUS, you still have that original unburned oxygen being detected as a too-lean condition. Burning excessive fuel in the catalytic converter overheats it and melts the catalyst. That is what CJ Medevac was describing. Once that melts, it blocks exhaust gas flow so the engine spends all of its power trying to blow exhaust gas through it. There's little power left to move the truck. The clue to a plugged converter is you will hear a steady hiss from the tail pipe instead of the normal "putt putt".

Before this serious damage occurs, the Check Engine light will start to flash. Flashing indicates the most serious of situations and you are supposed to stop the engine right away and let the exhaust system cool down. It does not mean keep on forcing the truck to move until you have the time or money to have it repaired.

While it is impossible to say for sure now, it is likely this all started with a failure to replace the spark plugs at the recommended interval. Ignoring the problem will only end up costing a lot more in the long run.

As for removing the catalyst material and leaving a hollow housing, that is really a bad idea. You will still end up replacing the converter anyway. The front oxygen sensor switches between "rich" and "lean" about two times per second when the engine is running properly. When the catalytic converter is doing its job, the gas coming out is mostly carbon dioxide and water vapor. There is another oxygen sensor after the converter that monitors that gas, and when the converter is working, it switches between "rich" and "lean" perhaps once every minute or two. As the converter loses its efficiency, less change takes place in the composition of the exhaust gas, so the rear oxygen sensor switches between states faster and faster. That is how the Engine Computer knows the efficiency of the converter. You want to remove all of the catalyst. That means there will be no difference between the exhaust coming in and going out, so both sensors will read exactly the same. That will turn the Check Engine light on right away.

With the Check Engine light on, there will be diagnostic fault codes stored associated with it. The Engine Computer performs a large number of self-tests while you are driving, and will set a fault code related to any problem it detects. There is always a long list of conditions that must be met to set a fault code, and one of those conditions is that certain other codes cannot already be set. By having a "catalytic converter efficiency" code already set, many self-tests that need that rear sensor's information will be suspended. If a problem related to one of those tests develops, it may go undetected because the computer is not doing those tests. You already want to ignore a very serious problem that we know is going to cause more trouble and expense. The Engine Computer is going to do the same thing by ignoring certain operating conditions. There are a lot of minor things that are easily corrected, if you know about them, and when you do not, they can become expensive.

The least expensive and most effective way to fix this is by doing it the right way, not by running to multiple shops hoping to find a different answer you like better. I would stop driving the truck until you can have it repaired. To prevent this from happening again, always stop the engine any time the Check Engine light is flashing.
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Friday, September 16th, 2016 AT 1:50 PM

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