P0171 - System Too Lean Bank 1

Grizzly Be4R said:
Mechanic didn't detect a vacuum leak. Changed the MAF (new Delphi) and also replaced the PCV valve+ gasket.

CEL stayed off for about 100 miles and then popped back on. P0171. O2 sensors are new as well. Any other suggestions? I'll try to get a smoke test done soon if that's my only option besides the fuel filter..
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Fuel filter is an inexpensive fix. OEM filters go for about $40 iirc. If the inlet and outlet nuts aren't rusted on yours I'd suggest doing it yourself, it's not a hard job as long as the nuts can thread easily. Perhaps give that a shot, especially if it's never been done on your truck before and report back. If you need the p/n let me know.

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If the fuel filter doesn’t fix it look for cracks on the intake tube between the MAF sensor and the throttle body.


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JoeT4R said:
Any further updates on this? My rig is now having the P0171, even after clearing the code three times now with my ScanGauge.

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I had this code in July and eventually tracked it down to either a dirty MAF or a vac leak, I'm not sure which it was because I did both at the same time and it hasn't come back since
 
RodrickHeffley said:
I had this code in July and eventually tracked it down to either a dirty MAF or a vac leak, I'm not sure which it was because I did both at the same time and it hasn't come back since
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Did you clean the MAF sensor or replace it?

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RodrickHeffley said:
just cleaned it with the cleaner from oreilly's, the MAF for the 98 runs pretty expensive new so that was the first (and cheapest) option I found
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I'll do some more research today and see what shows up.
Doc2012 said:
Mine was a partially clogged fuel injector.


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How did you end up discovering that it was a fuel injector?

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JoeT4R said:
How did you end up discovering that it was a fuel injector?

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Deductive reasoning.

Cleaned, tested, and replaced everything that the FSM said was related to the 171; and it still showed up.

So then I moved onto the fuel system; replaced the filter with no change; tested the pump (within spec); ohmed out the injectors (within spec).

Just for poops and giggles I bought an ultrasonic cleaner and injector tester; put all 6 in the cleaner with dawn for about an hour, then pulsed each one for about 30 minutes in the cleaner; then put them back in with fuel system cleaner (to try and get rid of water).

Bam.

No more 171.


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Doc2012 said:
Deductive reasoning.

Cleaned, tested, and replaced everything that the FSM said was related to the 171; and it still showed up.

So then I moved onto the fuel system; replaced the filter with no change; tested the pump (within spec); ohmed out the injectors (within spec).

Just for poops and giggles I bought an ultrasonic cleaner and injector tester; put all 6 in the cleaner with dawn for about an hour, then pulsed each one for about 30 minutes in the cleaner; then put them back in with fuel system cleaner (to try and get rid of water).

Bam.

No more 171.


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I see. That's good to hear you were able to work the process like that. And I appreciate the information on that. I actually went ahead and ordered a new Denso MAF sensor from RockAuto. Should be here in two days. I'll throw that in and see where it takes me. I haven't noticed a decrease in overall performance or mileage, I've recently done my A/F ratio sensor and o2 sensor, and the fuel filter.

If the new MAF sensor doesn't resolve the CEL, then I'll continue working the problem with some of the things you did. Hopeful that it's just the sensor itself.
 
Doc2012 said:
Deductive reasoning.

Cleaned, tested, and replaced everything that the FSM said was related to the 171; and it still showed up.

So then I moved onto the fuel system; replaced the filter with no change; tested the pump (within spec); ohmed out the injectors (within spec).

Just for poops and giggles I bought an ultrasonic cleaner and injector tester; put all 6 in the cleaner with dawn for about an hour, then pulsed each one for about 30 minutes in the cleaner; then put them back in with fuel system cleaner (to try and get rid of water).

Bam.

No more 171.


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Click to expand...


It’s fairly easy rebuilding the injectors. I have how I did it in my build and repair thread with the rebuild kit.


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P0171 system too lean bank 1

I’ve replaced my fuel injectors fuel pump intake manifold gaskets o2 sensors tps sensor vaccum lines fuel filter and maf sensor I’m still getting a p0171 code a mechanic told me it was the fuel pump and said it was at 28psi instead of 33-38 psi so that’s why I replaced it again I believe it might be my catalytic converter I just had recently changed about 7 months ago bc it sounds weird what do you guys think it could be I’ve replaced literally everything pertaining to the code p0171 I wanted to post my own thread but it wasn’t letting sorry so I tagged along on yours I’ve gotten it smoke tested also it’s not the vacuum lines I’m completely at a lost besides the catalytic converter any help would be appreciated
 
Josiah21 said:
My 4Runner will get to 70 mph and will struggle to go past it that’s why I’m trying to fix the issue
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When was the fuel filter changed, and the fuel pressure good? A other possibility is injectors plugged up.

Does it always cut out at that rpm level ?

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Josiah21 said:
I’ve replaced my fuel injectors fuel pump intake manifold gaskets o2 sensors tps sensor vaccum lines fuel filter and maf sensor I’m still getting a p0171 code a mechanic told me it was the fuel pump and said it was at 28psi instead of 33-38 psi so that’s why I replaced it again I believe it might be my catalytic converter I just had recently changed about 7 months ago bc it sounds weird what do you guys think it could be I’ve replaced literally everything pertaining to the code p0171 I wanted to post my own thread but it wasn’t letting sorry so I tagged along on yours I’ve gotten it smoke tested also it’s not the vacuum lines I’m completely at a lost besides the catalytic converter any help would be appreciated
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Exhaust leaks or a bad air/fuel sensor can also cause P0171.
 
With all that changed, I would definitely look at the cat. Shine a flash light through it. to see if its clogged. Being [MENTION=388984]jross20[/MENTION] just had a pinging issue with one. Its definitely possible. Plus a possible vacuum leak
 
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