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Discussion Starter · #1 ·
I used to run K&N filters in all my vehicles so putting one in the FJ was just a normal "mod" till my MAF started throwing codes on my Torque+ App.
A little research and out came the K&N, removed and cleaned the MAF with MAF cleaner spray, reset codes... still threw an error after about 50 miles.
OK, new MAF... same deal after about 100 miles p0171 popped up again. Maybe a defective MAF? Replaced, cleaned electrical connector, reset codes... Same deal...
Then po430 started showing up. Coming back from PA on a trip right after a fill-up it started to go into limp mode, to the point of literally dying under full throttle. Next stop i added about 3 bottles of HEET just in case it was water in the fuel. So it runs OK for a while... until it started happening more frequently... and I got error codes for just about everything fuel related.

Took a Toyota tech for a ride, showed the MAF readings live and Fuel Trim graphs running as we drove... He said you have an air leak... So I pay $90 for them to "smoke" test for leaks - nothing! He hooks up a fuel pressure tester and says you have a bad fuel pump - only 34psi instead of 42psi - $1200 to replace.
Well, that's a no-brainer, purchase the URD Walbro high volume pump and external NAPA filter upgrade and install... Yep lotsa black stuff in the filter housing and rusty stuff coming out of the fuel pump.. Problem solved!!
So reset all codes... go for a test drive.. no more hesitation but got pending p0430 and pending p0171 within the first 2 days of driving to work.

Meanwhile, after smashing a muffler on the rocks at SOR, I replaced the exhaust system with a true dual free flowing cat-back custom system, but all cats were left alone. I had the tranny out for a clutch job and cleaned and put di-electric grease into all the electrical connectors so no loose connections there either...

I can't believe that 3 MAF sensors all went bad... I haven't touched anything on the intake since the smoke test so no leaks... Don't feel like spending $$$$ on a new Catalytic and feel that the problem is upstream unless the MAF situation is dumping a rich mixture and causing Cat failure...

Any ideas or suggestions on where to start? I just set up my Torque+ app to monitor bank 2 Cat temps and voltages at pre and post O2 sensors and will see what that shows tonight...
Still no clues as to why the repeated MAF errors???

2008 MT
Current mileage 145k
 

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You are not not going to like this but the problem is likely to be the cats. The computer is detecting a signal from the oxygen sensors that is out of bounds. The first reaction is to replace the sensors because it's easier and cheaper. The primary cats are probably at fault and that sucks because they are a one piece assembly with the exhaust manifold. The manifold bolts are accessible from the wheel wells but all the bolts/nuts for the exhaust tend to act like they are welded for all eternity when you try to remove them. If you decide to replace the cats do the primarys first and see if the codes clear. If the codes clear you are good to go, if not then go to the secondaries. I had to replace mine and it was just the primarys. A friend also had this issue and the dealer did the secondaries first because it was cheaper but they were OK and the primaries still had to be replaced. Buy a Scan Gauge or other reader that can clear codes and you can avoid the limp mode by clearing the computer. The codes will come back until you get it fixed but at least you can still drive.
 

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(minor threadjack)
With the torque app... are you able to clear codes?
 

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Discussion Starter · #5 ·
You are not not going to like this but the problem is likely to be the cats. The computer is detecting a signal from the oxygen sensors that is out of bounds. The first reaction is to replace the sensors because it's easier and cheaper. The primary cats are probably at fault and that sucks because they are a one piece assembly with the exhaust manifold. The manifold bolts are accessible from the wheel wells but all the bolts/nuts for the exhaust tend to act like they are welded for all eternity when you try to remove them. If you decide to replace the cats do the primarys first and see if the codes clear. If the codes clear you are good to go, if not then go to the secondaries. I had to replace mine and it was just the primarys. A friend also had this issue and the dealer did the secondaries first because it was cheaper but they were OK and the primaries still had to be replaced. Buy a Scan Gauge or other reader that can clear codes and you can avoid the limp mode by clearing the computer. The codes will come back until you get it fixed but at least you can still drive.
Here's a screenshot of the CAT data - Bank 2 cat temp sensor 1 & 2; Bank 2 Wideband o2 voltage & post CAT voltage; fuel status.

Should CAT post temps be higher than input?

Yes the Torque+ app clears codes...
I haven't been running a K&N for months, removed it and cleaned out everything then just running stock paper filter. This was when I first cleaned the MAF sensor.
 

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Discussion Starter · #6 · (Edited)
According to the aa1car.com library:


There are several ways to detect a restricted, plugged or worn out converter using a scan tool. Here's what to look for

* A significant difference in Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values between the right and left cylinder banks on a V6, V8 or V10 engine. If you see such a difference and the vehicle has separate converters for each cylinder bank, one of the converters may be plugged.

* A lower than normal barometric pressure (BARO) value. If your engine has a Mass Airflow (MAF) sensor, and the engine computer uses the signal from the MAF sensor to calculate a barometric pressure (BARO) value, the calculated value may be lower than normal is the exhaust is restricted.

* A lower than normal Manifold Absolute Pressure (MAP) sensor value. A restricted converter will cause an increase in backpressure that reduces intake vacuum.

All of these look good when running the vehicle scanning all the above plus vacuum, everything responds as its supposed to.
 

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According to the aa1car.com library:


There are several ways to detect a restricted, plugged or worn out converter using a scan tool. Here's what to look for

* A significant difference in Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values between the right and left cylinder banks on a V6, V8 or V10 engine. If you see such a difference and the vehicle has separate converters for each cylinder bank, one of the converters may be plugged.

* A lower than normal barometric pressure (BARO) value. If your engine has a Mass Airflow (MAF) sensor, and the engine computer uses the signal from the MAF sensor to calculate a barometric pressure (BARO) value, the calculated value may be lower than normal is the exhaust is restricted.

* A lower than normal Manifold Absolute Pressure (MAP) sensor value. A restricted converter will cause an increase in backpressure that reduces intake vacuum.

All of these look good when running the vehicle scanning all the above plus vacuum, everything responds as its supposed to.

I don't think the cats are plugged up. When I had the P0340 issue the FJ drove fine as long as I kept the codes cleared. What I think has happened is that the primary cats have lost efficiency and this causes too big of a variance between the 1st and 2nd oxygen sensors. The cat failure is I think partially due to an overrich condition while the engine is warming up and could have been worsened by your KN filter oil. Toyota has acknowledged that this is an issue and this is likely the reason that the newer FJ's have the air pump that gets in the way of dual battery setups. I was fortunate in that I live in California and mine failed about a week before I drove over the extended smog component warranty mileage so I didn't have pay for the repair. It was well over 2 grand for my friend who had all 4 cats replaced. It might be worth inquiring about a Technical Service Bulletin at the dealer, Toyota might pick up part of the tab if your intake system looks stock. I'm sure they would blow you off if the KN filter were still there.
 

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When you see a P0430 "catalytic converter efficiency" code in conjunction with other codes, always address the other codes first, as they can be the root cause of the P0430.

You seem to have immediately focused on a defective MAF as a factor. Which codes did you think were associated with a MAF failure? Neither P0171 or P0430 are directly linked to the MAF sensor. And you're 100% correct, the probability of three MAF sensors "going bad" in the same vehicle within a very short period of time is astronomically small. The Toyota MAF sensors are extremely reliable, and almost never truly "fail". They can get contaminated, and can be physically damaged by clumsy attempts to clean them, but they rarely fail spontaneously.

Let's look at the P0171 code first. What is the literal description? "System too lean - Bank 1". What does this mean? It means that the ECU "thinks" that it received valid data indicating that the passenger side cylinder bank is running too lean, and requires a larger than normal correction ("fuel trim") to bring it back towards the target 14.7:1 air-fuel ratio.

So, what could cause the ECU to think Bank 1 (but NOT Bank-2) is lean? Probably NOT the MAF sensor, because the single MAF sensor provides air flowrate data for BOTH cylinder banks, and as far as we know, bank-2 is running just fine.

So the pertinent questions are:
1. What could make one cylinder bank run lean, while the other one apparently is running within spec?

2. Is it possible that the ECU is receiving bad data for the Bank-1 mixture, and it's not really running lean?

For question #1 , a partially clogged fuel injector or a localized intake manifold leak affecting only one cylinder bank could create a true lean condition. Low fuel pump pressure or an air leak between MAF and intake manifold would affect both cylinder banks. However, if one bank was truly running excessively lean, you might encounter some drivability problems, like detectable hesitation under initial acceleration.

For question #2 , it is very possible for the ECU to be getting bad data from the Bank-1 air-fuel and/or oxygen sensors, depending on age, mileage, state of engine maintenance, etc. If these sensors have more than 85K miles on them, their response time may be getting "slow", or their output voltage may no longer met the original specifications.

If there are no obvious driveability problems that would be associated with a true lean-mixture problem, I'd suspect the air/fuel and oxygen sensors, and replace them before doing anything else. Given that this vehicle is more than six years old, and has 145K miles on the odo, does it still have the original air-fuel and oxygen sensors? If so, they are likely past their expected service life, even if the engine has been maintained in perfect operating condition.

After resolving the P0171 code, we can look at the P0430 code. However, in many cases simply replacing the air-fuel sensor and the oxygen sensor on the affected cylinder bank will resolve BOTH the P0171 and P0430 codes.
 

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Discussion Starter · #9 ·
When you see a P0430 "catalytic converter efficiency" code in conjunction with other codes, always address the other codes first, as they can be the root cause of the P0430.

You seem to have immediately focused on a defective MAF as a factor. Which codes did you think were associated with a MAF failure? Neither P0171 or P0430 are directly linked to the MAF sensor. And you're 100% correct, the probability of three MAF sensors "going bad" in the same vehicle within a very short period of time is astronomically small. The Toyota MAF sensors are extremely reliable, and almost never truly "fail". They can get contaminated, and can be physically damaged by clumsy attempts to clean them, but they rarely fail spontaneously.

Let's look at the P0171 code first. What is the literal description? "System too lean - Bank 1". What does this mean? It means that the ECU "thinks" that it received valid data indicating that the passenger side cylinder bank is running too lean, and requires a larger than normal correction ("fuel trim") to bring it back towards the target 14.7:1 air-fuel ratio.

So, what could cause the ECU to think Bank 1 (but NOT Bank-2) is lean? Probably NOT the MAF sensor, because the single MAF sensor provides air flowrate data for BOTH cylinder banks, and as far as we know, bank-2 is running just fine.

So the pertinent questions are:
1. What could make one cylinder bank run lean, while the other one apparently is running within spec?

2. Is it possible that the ECU is receiving bad data for the Bank-1 mixture, and it's not really running lean?

For question #1 , a partially clogged fuel injector or a localized intake manifold leak affecting only one cylinder bank could create a true lean condition. Low fuel pump pressure or an air leak between MAF and intake manifold would affect both cylinder banks. However, if one bank was truly running excessively lean, you might encounter some drivability problems, like detectable hesitation under initial acceleration.

For question #2 , it is very possible for the ECU to be getting bad data from the Bank-1 air-fuel and/or oxygen sensors, depending on age, mileage, state of engine maintenance, etc. If these sensors have more than 85K miles on them, their response time may be getting "slow", or their output voltage may no longer met the original specifications.

If there are no obvious driveability problems that would be associated with a true lean-mixture problem, I'd suspect the air/fuel and oxygen sensors, and replace them before doing anything else. Given that this vehicle is more than six years old, and has 145K miles on the odo, does it still have the original air-fuel and oxygen sensors? If so, they are likely past their expected service life, even if the engine has been maintained in perfect operating condition.

After resolving the P0171 code, we can look at the P0430 code. However, in many cases simply replacing the air-fuel sensor and the oxygen sensor on the affected cylinder bank will resolve BOTH the P0171 and P0430 codes.
Resurrecting this thread...

These were the items that a search on the P0171 brought up:

Possible causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

P0171 TOYOTA Air/Fuel Mixture System Lean Bank 1 | AutoCodes

There were no misfire symptoms
At the time there was no fuel pressure issue
PCV checked out fine
A smoke test was run by the dealer for intake leaks
The wideband O2 readings on the Torque+ app were within spec

Since I had just recently completed a K&N air filter re-charge and a quick search indicated that too much oil on the filter would cause MAF issues, the focus went to a readily accessible, easy to clean, component.

After this post, further diagnostics showed fuel pressure to be out of spec so the factory pump and filter were replaced with the URD Hi-Volume unit.

The P0430 continues to come and go. The exhaust has always been very black for years.

I'm replacing the O2 sensors and Cats in a couple weeks, but I'm still not sure why the ECY says lean system and the exhaust clearly shows the opposite?
 

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Discussion Starter · #10 ·
Long tube headers, magnaflow cats, a modified non-fouler on the post flow sensor and no more p0420/0430 codes!
 

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Having to replace my bad front cats. So the long tube headers without front cats will work and pass emissions?

Sent from my LG-H830 using Tapatalk
 

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Resurrecting this thread...

These were the items that a search on the P0171 brought up:

Possible causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

P0171 TOYOTA Air/Fuel Mixture System Lean Bank 1 | AutoCodes

There were no misfire symptoms
At the time there was no fuel pressure issue
PCV checked out fine
A smoke test was run by the dealer for intake leaks
The wideband O2 readings on the Torque+ app were within spec

Since I had just recently completed a K&N air filter re-charge and a quick search indicated that too much oil on the filter would cause MAF issues, the focus went to a readily accessible, easy to clean, component.

After this post, further diagnostics showed fuel pressure to be out of spec so the factory pump and filter were replaced with the URD Hi-Volume unit.

The P0430 continues to come and go. The exhaust has always been very black for years.

I'm replacing the O2 sensors and Cats in a couple weeks, but I'm still not sure why the ECY says lean system and the exhaust clearly shows the opposite?
Do you have an update on your code issue. I have the same issue now without the K&N product.

Gary
 

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Discussion Starter · #14 ·
Do you have an update on your code issue. I have the same issue now without the K&N product.

Gary
Yes and no...
I have not had the P)171 code anymore after the fuel pump replacement.
I upgraded to long tube headers, free flow cats and dual exhaust system.
As a result I am continually getting to P0420/0430 codes for inefficient CAT because it cant read the flow of then performance system.

I do have a brand new MAF sensor left over from that exercise if that what proves to be wrong in your case - I'll give you a decent deal on it.

Switching to the URD fuel pump and filter is a win-win, more volume and an external filter easy to replace with a NAPA unit...
The dealer quote to replace the in-tank pump and filter was $1200.
Upgrading to the URD is a little above basic skills, best to have a buddy or a transmission jack and an empty fuel tank. You can only get the wires disconnected from under the left passenger rear seat, the hole is stupidly too small to remove the fuel pump!! So dropping the tank is a must.

Hope that all helps...
 

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Thanks for the reply and I am going to drop the tank and get a new fuel pump. Ya gotta do what ya gotta do.

Gary
 

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Discussion Starter · #17 ·

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Yeah, they're right about the access panel solution. Their FJ is filthy.... and ******* is an understatement....
Replace it with the URD/Walbro pump and pretty sure it will be the last time you need to get in there...
yeah i would replace the pump also , wonder how much dirt fell in the gas tank with these idiots lol

Agreed... the amount of dust that rolled out of the back seat was crazy, but on another angle, I admire the ingenuity. They definitely are not afraid of breaking anything and I guess if you are going to abuse it, you better know how to fix it.

I try and take care of stuff, because when I break something I often have to pay someone else to fix it.
 

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Discussion Starter · #20 ·
With the headers etc, get the URD SIM and your P0420/P0430 codes go away, plus I gained 2-3 mpg...
 
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