P0171 Lean Bank Issue, Help !

Here we go again....ugh

2002 Toyota Tacoma SR5

Check engine light back on.

Replaced

1. ) Fuel Filter
2. ) Both oxygen 2 sensors, upstream and downstream. ( Abigail - aftermarket )
3. ) Air Filter
4. ) MAF sensor
5. ) Fuel Injector Pressure Regulator

Also checked for air or hose leaks and none.


After putting pressure regulator in and cleared code, drove 10 miles and check engine light
comes back on ?

I'm getting awful gas mileage, like 12 miles per gallon ?

Took it to Toyota dealer a few weeks ago and the wanted $2,000 to replace timing belt, water pump and gaskets and fuel pressure regulator ? LMAO

The timing belt is off by a tooth and idles good, not great. Could that be the cause of a lean bank code ?


I'm just so frustrated. Bought the truck 6 weeks ago with 153,000 miles on and CEL goes on
the moment I drove away from the deal. Joke on me, ugh

Any help would be much appreciated.

Stan

 

yes to the timing belt causing the issue. get her back in time and it "should" be OK.

 

I've never heard of a p0171 being thrown due to the timing belt being off, but that is still an issue that should definitely get fixed. A trusted private mechanic should be able to do that for you for much cheaper.

P0171 is almost always a vacuum leak, even a tiny one can trip the code. Check the throttle body, the intake tube can get dry and cracked over the years. As well as all the lines running to and from it, use carb cleaner to search for leaks.

A leak or crack in the exhaust can also trip that code. I chased a P0171 for a frustratingly long time and in the end, for me it was a small cap on the back of my supercharger had come slightly loose.

 

Had a lean code on my 3.4 around the same mileage ended up being a bad fuel injector

 

I feel your pain, like I said in a previous post I went through a similar nightmare because of P0171...it's a tough code to pinpoint because it can be so many different things, but I still think it's most likely a vacuum leak. A small crack in a hose or a tiny loose connection somewhere will throw the code. Gotta be very thorough in checking every line and rubber hose fitting. Usually if it's related to the exhaust, or your O2 or A/F sensors then you'll get other codes as well. Check for leaks in the engine bay

 

Timing will not have anything to do with your lean code. Surprising you didn't get a p0300 for random misfire, but all the mark can be correct and belt installed off which wouldn't matter in that case.

Assuming this is a 5vz, check your driver side valve cover, toward the rear in front of the firewall, you'll have a vacuum hose going to intake. That hose had my buddy running around like a chicken without a head cause the hose cracked at nipple cause major leak. His stft and ltft was way off.

If all check out, might be bad fuel pump or leaking injector.

 

Ok, I disconnect the neg terminal, CEL goes off, drive 5 miles, CEL comes back on.

 

If it was a bad fuel pump or leaking injector why would the truck run, start, and idle smooth in some cases ?

This is a Tacoma V6 3.4

 

Your lean code is major in my opinion if it's triggering the mil light that fast. I'm leaning towards leaking or clogged injector and or bad fuel pump

 

Yes. Truck will start, run, and idle. All you're doing is starving the engine of fuel thus causing a lean code. You can have 1 crack head on 2 cylinder and your truck will start and run.

Bad fuel pump don't mean pump is not working completely. Pump might be at est 40% cycle instead of full capacity.

Leaking or clogged injector will still have fuel mist, just more air then fuel. Causing it to run lean.

 

Sounds like fuel injector to me but odd your not getting a misfire code with your lean code.

 

Check thoroughly for vacuum leaks. Did you work on anything prior to the lean code coming in?

 

this is a very good explanation of what is going on...

https://repairpal.com/obd-ii-code-p0171

sorry for the frustration.

 

yes, read this article last week, thanks

 

What about a bad or weak fuel pump ?

This is what I found online.


2. Difficulty starting
Another symptom that is commonly associated with a problematic fuel pump is difficulty starting. Because of how they operate (constantly running whenever the ignition is turned on) over time fuel pumps can eventually wear out and weaken. A weak fuel pump may still pump fuel, however the vehicle may experience difficulty starting as a result of the lack in pressure. A weakened fuel pump can cause the vehicle to take more cranks to start than normal, and in more serious cases may even cause the vehicle to require multiple turns of the key before it will start.


3. Misfires and a decrease in power, acceleration, and fuel efficiency
Another symptom of a problem with the fuel pump is engine performance issues. As the fuel pump is what supplies the vehicle with the fuel required for combustion to occur, any issues with it can affect the engine’s fuel supply and cause issues. A faulty pump with low pressure will disturb the engine’s air-fuel ratio, which can cause all sorts of performance problems. Aside from hard starting, the vehicle may experience misfires, a loss in power and acceleration, a decrease in fuel efficiency, and even engine stalling.

 

stab in the dark again... how long will the power brake booster hold vacuum for after you shut the truck ? I am thinking maybe the diaphragm is questionable.

 

My truck just threw this code yesterday on the way to work. I reset the code and drove 30 miles home and the CEL didn't come back on. So I'm going to clean the MAF and check for vacuum leaks this weekend.

 

As you have found, disconnecting the battery does not fix the underlying problem causing the malfunction.

All of the Tacoma's I've owned have thrown codes more frequently then any other vehicle I've owned. I've had the P0171 in conjunction with other codes. In my case it was the A/F sensor.

Follow the diagnostics in the attached doc from the FSM. A systematic approach to the problem will work better than random stabs in the dark.

 

These engines prefer Denso sensors. That's not to say the others can't work, but it seems most of us have better results with the OEM part.

 

Your A/F sensor is upstream, before the cat. Your O2 sensor is downstream, after the cat.