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Discussion Starter #1
Okay I have a 2000 prerunner 2x4 Trd 3.4L. roughley 80,000 miles. The only engine mods it has are an k&n intake and magnaflow exhaust. My check engine is on the OBD code is P0171 (system too lean (bank 1)). Which would refer to the first O2 sensor. So I bucked up and bought both 02 sensors (genuine toyota parts) and installed them. Then i reset the computer, and everything was good. After about 20 miles its back on, and I'm frustraited as hell after spending $400 on 02 sensors, please someone help me, I'd greatley appreciate it.
 

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First step I'd say is to check the MAF element and see if it's dirty. A lot of folks running oiled filters here seem to run into that code (as well as bank II) due to a dirty MAF. Auto parts stores usually have a MAF specific aersol cleaner, pick up a can and give it a shot.

A clogged B1 fuel injector, vaccum leaks or upstream leaks in the exhaust could also trigger a lean code.
 

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i have the same issue on my scharged 3.4L. will this cause permanent damage to the engine?
 

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scottmc said:
Okay I have a 2000 prerunner 2x4 Trd 3.4L. roughley 80,000 miles. The only engine mods it has are an k&n intake and magnaflow exhaust. My check engine is on the OBD code is P0171 (system too lean (bank 1)). Which would refer to the first O2 sensor. So I bucked up and bought both 02 sensors (genuine toyota parts) and installed them. Then i reset the computer, and everything was good. After about 20 miles its back on, and I'm frustraited as hell after spending $400 on 02 sensors, please someone help me, I'd greatley appreciate it.
I dealt with the same issue and the same exact sysmptoms as you are describing in a corolla, and the problem was a bad MAF sensor. It was dirty also, but cleaning it didn't help. And after resetting the computer, the CEL would come on about 20 miles later. He had a stock intake with a stock filter though. So, either the MAF just failed on its own, or the K&N filter was over oiled. If I were you, after fixing the problem I would ditch the K&N and throw the stock intake back on (assuming you still have it), and do either the deckplate or elbow mod to it.
 

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I cleaned my MAF, O2 sensors and disconnected the battery to reset the computer. My light still turns on after a few miles of driving. What gives?
 

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how do i richen up the a/f ratio w/o gettin the 7th injector set-up?
 

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Not my department contact urdusa.com :shrug:

You could be running lean for other reasons though. Have you always had a lean code since you put the blower on?
 

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OK check to see if you have an intake leak, but seriously cleaning the MAF doesnt work all the time. I would check to see there is not leak and then check the Brake booster line. Some years the booster leaks and causes the 171 code. If you do not have any leaks. 100% your MAF is bad.
 

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Supercharged truck still has fuel control via MAF, even though its forced induction the MAF still controls the fuel ratio. If your still getting that code then you have a bad MAF. I see this problem once in awhile on SC 3.4L engines. Unless there is a vacuum leak due to a vacuum cap that came off during the boost..

To be honest you will need to look at the freeze frame data for the fuel trim.
 

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BatuKing said:
Supercharged truck still has fuel control via MAF, even though its forced induction the MAF still controls the fuel ratio. If your still getting that code then you have a bad MAF. I see this problem once in awhile on SC 3.4L engines. Unless there is a vacuum leak due to a vacuum cap that came off during the boost..

To be honest you will need to look at the freeze frame data for the fuel trim.
Yeah but how many pounds of boost are we talking about and what is a non-modified fuel management system capable of adapting to?

Too many variables, not enough info.

Oh, and a $150 MAF is a pretty big dart to throw at a truck off of a hunch dude, what do I know though. :shrug:
 

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Discussion Starter #15 (Edited)
after cleaning my MAF all was well til about 140 miles and then my light came back on. i haven't checked the codes again but i'm assuming that its the P0171 (which is what it had previousley been). does anyone know what voltages should be present at the MAF when it is operating. or is there any other way to figure out what might be tripping the light, keep in mind i just replaced both 02 sensors. also i'm not sure if i mentioned to add in the first post, that the first time the light came on as this past april. and i had it checked and the mechanic said no big deal, its running lean cause your K&N. I knew its wasn't the K&N itself cause i've had it on for about 40K+. the truck drove fine so that's why i delayed fixing it for so long. then i got my smog notice and thats why i've waited so long to solve this. since i've waited so long on a 171 code could that have cause further damage somewhere else. my truck has bee running fine with no real noticable change throughout this peeriod though. hope i didn't sound like too much of an idiot there
 
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