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Low Power issue HELP ME

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13 Aug 2019 17:59 #32785 by Jace
Low Power issue HELP ME was created by Jace
I hooked up a vacuum gauge due to a loss of power and misfire under high load. Engine has 200k vacuum gauge is 16inhg and steady leading me to late ignition timing. from my understanding the timing can't be adjusted on a COP system. Do I need to do a crank relearn or how do I fix this

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13 Aug 2019 18:24 #32786 by Cheryl
Replied by Cheryl on topic Low Power issue HELP ME
What kind of car is it??

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13 Aug 2019 18:39 - 13 Aug 2019 18:40 #32787 by Jace
Replied by Jace on topic Low Power issue HELP ME
2001 GMC Sierra 5.3 liter engine
Last edit: 13 Aug 2019 18:40 by Jace.

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13 Aug 2019 19:58 #32791 by Cheryl
Replied by Cheryl on topic Low Power issue HELP ME
What do the oxygen sensors do? Do they go rich when the no power happens?? Or lean out??

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13 Aug 2019 21:10 #32797 by Jace
Replied by Jace on topic Low Power issue HELP ME
Oxygen sensors look as they should. Fuel delivery looks good to.

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13 Aug 2019 21:30 #32798 by Cheryl
Replied by Cheryl on topic Low Power issue HELP ME
They go full rich? As in close to 1 volt both banks?? If so I’d definitely pull the oxygen sensors out and check the exhaust back pressure with a back pressure gauge

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13 Aug 2019 21:31 #32799 by Cheryl
Replied by Cheryl on topic Low Power issue HELP ME
It’s almost got to be a clogged converter
The following user(s) said Thank You: Noah

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28 Aug 2019 14:02 #33225 by rpd1125
Replied by rpd1125 on topic Low Power issue HELP ME
I just had one doing exact thing. if you can get your hands on a back pressure gauge they will save you so much time This clearly sounds like a clogged catalytic converter. That back pressure gauge simply threads into the upstream o2 sensor port and you rev the engine. it should be easily on the green at idle and if it goes to red scale then you have a clogged Catalytic converter.
From what I remember these Cats are serviced as one unit and don't forget to get the new gaskets for both sides they never seal right when reused especially the driver side one which is a crush ring style but get both and save yourself the headache

hope it helps

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