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Discussion Starter #1
hi guys,
on my way home from a hour trip my 99 blazer (trailblazer) started to hesitate & as i continued to drive it got worse until i could barely go anymore. An hour later when the wrecker showed up to tow it it fired right up & ran fine. When i got home I got out the code reader & it gave me P0131. It only seems to act up when it gets fully warmed up.

My question is: is the drivers 02 sensor bad or is it something else like maybe EGR or MAF?

i also replaced the fuel pump & filter last year so i doubt it would be that.

any help would be appreciated....
 

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Age: 15 1/2
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Bad O2 sensor or wire?
Leak in exhust manifold when hot?
Plugged exhust?
Bad injector or leaky fuel injection?
 

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Discussion Starter #3
Bad O2 sensor or wire?
Leak in exhust manifold when hot?
Plugged exhust?
Bad injector or leaky fuel injection?

Bill,
When it was acting up i didnt hear any exhaust leaks under the hood.
I didnt smell any gas like it was leaky injector.

Seems odd that it only happened when hot & if i let it cool down it was fine till it got warmed up again.

thanks for the input. I'll try to play with it tonight & see if i can get something figured out....
 

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Age: 15 1/2
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The Cat is easy to test. Connect a vacuum gauge, Hold the rpms up to about 2.5K. If it's plugged the reading will drop steady to near zero.

The hard part is what caused it to fail. If it is an over rich mixture, then you can probably clean it out.
 

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You're getting a low voltage signal from Bank 1 Sensor 1. That is the one on the driver's side ahead of the cat. Low voltage means that the sensor is dying or something happened to the connection. Not much chance that it has anything to do with the cat. Get a new sensor from Delco or Standard Motor Products and that should take care of it. Click here for more info.
 

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Discussion Starter #8
thanks guys, i'll do the test on the cat and see if thats it. if not probably be replacing the o2. will let you know what i find out...
 

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Discussion Starter #12
Have you checked your fuel filter? Same happened to me, fuel filter was clogged.
i replaced that last year when i replaced the fuel pump. wouldnt it run crappy all the time if the filter was clogged? the truck starts up fine but when it gets fully warmed up it acts up...

btw, it has 130k on it.

thanks glad to be here, i was on the blazer forum site, but for some reason i couldnt post anything so i moved to a better site :)
 

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When it starts up, it's running in "Open Loop" because it is not warmed up and the O2 sensors don't even work until they get to 600* F. After the engine Coolant Temp reaches a certain point, it may be 135* F., the engine goes into "Closed Loop" and starts running off of the O2 sensors. But your sensor is putting out too little voltage, which is read as a lean condition, and the PCM floods that bank with fuel to compensate, so the motor runs rough, because it is too rich.

A clogged fuel filter could also cause a lean condition, but it would be hard to start and run rough all of the time.
 
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