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Engine power fade/ loss at higher RPMs?? Low voltage (lean) front O2

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#1 Motodrew

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Posted 12 April 2017 - 12:43 AM

Hey gang,


First things first, here's what I'm experiencing:   My 2001 S10 4.3 ZR2 pickup appears to lose power and has troubles climbing in RPMs above about 3,000.  Trucks starts and idles perfectly. It feels strong and runs hard up until about 3,000RPM at which point the power drops off and it has a slow climb to redline.  This issue was magnified when I attempted to go up in elevation outside Denver.  The truck began to hiccup and stutter in an attempt to climb the hills.  Normal day to day driving to/from work there is no signs of issues.  Only noticeable when needing higher RPMs.  The only engine code I'm receiving is both bank1 & bank2 O2 sensors voltage low (or lean).  


I've replaced both front O2 sensors.   I've checked the fuel pressure and it was consistently 50psi+ as I drove around locally for a brief amount of time.  (Perhaps I need to perform a longer test.)  MAF sensor was thoroughly cleaned as well as the sensor behind it.  I've got a new distributor cap & rotor as well as a new fuel filter arriving in the mail tomorrow.


Any experiences or direction you all could share would be greatly appreciated.  I'd really like to save myself from throwing a bunch more money into this thing.   I'd like to get it running well so I can sell it soon. :)



Edited by Motodrew, 12 April 2017 - 12:46 AM.

#2 jderekt

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Posted 12 April 2017 - 12:52 AM

Plugged catalytic converter.

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#3 babydeuce

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Posted 12 April 2017 - 06:54 AM

I would investigate the MAP sensor...You should be able to google electrical checks for that sensor and get a pretty decent idea of if it is good of not.

#4 gsmobile2007

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Posted 12 April 2017 - 04:35 PM

How clean is the air filter, but I would bet jderekt is right with a cat thats going bad, those front O2 sensors probable got cooked by the higher back pressure holding in the heat, it's still open enough to let low to moderate flow but once the throttle body is fully open the cat cant pass gas (exhaust wise), and we all know what ist's like to be plugged up. Maybe the muff (ler) but you'll need to do your own muff diving.

#5 iCrash

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Posted 12 April 2017 - 06:28 PM

I would say its the catalytic converter too. My Blazer would go fine until you tried to either A - merge in traffic or B - go up a hill. I used a bluetooth ODBII adapter and the Torque Pro app to read the voltage differences between the upstream and downstream O2 sensors and was able to determine that something was wrong with the cat (you can find the exact procedure online). I replaced the cat with a direct fit and it solved my problem.

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