LTFT high except at idle and WOT ???

[gamefreakgc]

I'm pretty sure bank 1 and bank 2 relates directly to the motor. Bank 1 being the side that has the number 1 firing cylinder and then of course bank two is the side that has the 2nd. And you can have a normal LTFT reading on one bank and a lean or rich reading on bank 2. This then tells you your situation is on that side of the motor.

Well, you can believe that if you want to. The error codes you get for lean/rich in a specific cylinder will throw a code for that exact cylinder. Plus the fuel on both sides of the engine share fuel pressure from the fuel crossover pipes located on the front and back of both fuel delivery pipes.

But like I said you can believe what ever you feel like you want to. I'm just trying to help you with what the scan gauge readings really mean. Here's where I get my info from, the factory service manual (from page D-11, or page 187 in the PDF version):

SHORT FT #1 Short-term Fuel Trim Bank 1 0 ± 20 %
LONG FT #1 Long-term Fuel Trim Bank 1 0 ± 20 %
SHORT FT #2 Short-term Fuel Trim Bank 2 0 ± 20 %
LONG FT #2 Long-term Fuel Trim Bank 2 0 ± 20 %

AFS B1 S1
Voltage Output of Oxygen Sensor Bank 1 Sensor 1
Idling: 0.1 - 0.9 V

AFFT B1 S1
Oxygen Sensor Fuel Trim Bank 1 Sensor 1
(Same as SHORT FT #1)
0 ± 20 %

O2S B1 S2
Voltage Output of Oxygen Sensor Bank 1 Sensor 2
Driving 50 km/h (31 mph): 0.1 - 0.9 V

On my gauge, sensor 1 shows as bank 1 and sensor 2 shows as bank 2. See the part where bank 1 sensor 1 is the "Same as SHORT FT #1"? Gotta trust that people know what they are talking about.

 

[tlib99]

Well, you can believe that if you want to. The error codes you get for lean/rich in a specific cylinder will throw a code for that exact cylinder. Plus the fuel on both sides of the engine share fuel pressure from the fuel crossover pipes located on the front and back of both fuel delivery pipes.

But like I said you can believe what ever you feel like you want to. I'm just trying to help you with what the scan gauge readings really mean.

I guess I would need an example cause a PO171 and a PO174 is code for lean banks 1 and 2. Maybe I don't understand how this tells you specific cylinder.

 

[tlib99]

Well, you can believe that if you want to. The error codes you get for lean/rich in a specific cylinder will throw a code for that exact cylinder. Plus the fuel on both sides of the engine share fuel pressure from the fuel crossover pipes located on the front and back of both fuel delivery pipes.

But like I said you can believe what ever you feel like you want to. I'm just trying to help you with what the scan gauge readings really mean. Here's where I get my info from, the factory service manual (from page D-11, or page 187 in the PDF version):

SHORT FT #1 Short-term Fuel Trim Bank 1 0 ± 20 %
LONG FT #1 Long-term Fuel Trim Bank 1 0 ± 20 %
SHORT FT #2 Short-term Fuel Trim Bank 2 0 ± 20 %
LONG FT #2 Long-term Fuel Trim Bank 2 0 ± 20 %

AFS B1 S1
Voltage Output of Oxygen Sensor Bank 1 Sensor 1
Idling: 0.1 - 0.9 V

AFFT B1 S1
Oxygen Sensor Fuel Trim Bank 1 Sensor 1
(Same as SHORT FT #1)
0 ± 20 %

O2S B1 S2
Voltage Output of Oxygen Sensor Bank 1 Sensor 2
Driving 50 km/h (31 mph): 0.1 - 0.9 V

On my gauge, sensor 1 shows as bank 1 and sensor 2 shows as bank 2. See the part where bank 1 sensor 1 is the "Same as SHORT FT #1"? Gotta trust that people know what they are talking about.

Sounds good! Thanks. I'm here to learn and appreciate your input. But please understand, I'm not on here challenging anyones knowledge, I am just confused cuz I've been studying all this recently, and the stuff you are telling me is not what I've come across in my research. I don't mean to affend anybody but if something doesn't reflect what I've researched shouldn't I ask how one comes up with their info and then look again at my way of thinking? So, yea, sorry for "questioning" you.

 

[gamefreakgc]

My truck just threw a P0171 two weeks ago. I was doing some maintenance work on the throttle body and the gasket was out of alignment and allowing air to seep in between the throttle body and supercharger housing. The truck threw a P0171 since it had unmetered air entering, which was picked up as unburnt oxygen on the first O2 sensor. A little bit of prodding and some MAF cleaner helped me discover the source of the leak. As you could probably guess, any air coming in through the throttle body wouldn't be specific to one side of the engine or another (especially since I have a supercharger, which compresses the air before distributing it).

There's a lot of opinions out on the internet, and not all of it is correct. Plus, our OBD-II system is very basic. It was released in 1996, the first year any vehicle had an OBD-II system. As you might guess, it's not very detailed and can be somewhat slow and confusing. For these 4Runner, I stick to what I can find in the service manual since it's how they designed the truck. Not saying all opinions out there are wrong, but may not be applicable to ours.

 

[tlib99]

You hit the nail on the head there. Confusing for sure. Yea that's weird that it didn't throw a PO171 and PO174, that kind of unmetered air isn't bank specific. But would understand that on a 4cyl though right?

 

[gamefreakgc]

You hit the nail on the head there. Confusing for sure. Yea that's weird that it didn't throw a PO171 and PO174, that kind of unmetered air isn't bank specific. But would understand that on a 4cyl though right?

Almost. You're so close! The P0171 code is triggered by the front O2 sensor, which for us in located before the main cat (second cat if you have California emissions). The P0174 code is triggered by the rear O2 sensor, after all cats. They don't take any data from the engine, only the exhaust. If it were specific to one cylinder, you would get a P0301-306 (304 if you only have a 4-cylinder), with P0300 meaning multiple cylinders. So if say I had a vacuum leak on the injector or intake manifold that only fed a specific cylinder like what you are referring to, that's the codes it'll throw. To be honest, I'm not sure which sensor picks this up, or perhaps it's the knock sensor. I just know it works!

The O2 sensors are the ones that determine our fuel trims. The data it logs is then taken in with readings from the MAF, injector signals and the fuel is increased or decreased based off those readings. But all this is happening lightning fast and always changing. The LTFT is sort of an "average" saying roughly how much fuel it's added or taken away over a long period of time. But like my scan gauge says it maxes out at 17.9% when it's supposed to be 20% (some have read up to 33%) it's not really that accurate.

 

[tlib99]

Almost. You're so close! The P0171 code is triggered by the front O2 sensor, which for us in located before the main cat (second cat if you have California emissions). The P0174 code is triggered by the rear O2 sensor, after all cats. They don't take any data from the engine, only the exhaust. If it were specific to one cylinder, you would get a P0301-306 (304 if you only have a 4-cylinder), with P0300 meaning multiple cylinders. So if say I had a vacuum leak on the injector or intake manifold that only fed a specific cylinder like what you are referring to, that's the codes it'll throw. To be honest, I'm not sure which sensor picks this up, or perhaps it's the knock sensor. I just know it works!

The O2 sensors are the ones that determine our fuel trims. The data it logs is then taken in with readings from the MAF, injector signals and the fuel is increased or decreased based off those readings. But all this is happening lightning fast and always changing. The LTFT is sort of an "average" saying roughly how much fuel it's added or taken away over a long period of time. But like my scan gauge says it maxes out at 17.9% when it's supposed to be 20% (some have read up to 33%) it's not really that accurate.

:redbrick: That is so weird. Ok help me clarify. You have the 3400 correct? And I assume you have 4 O2s? Ok, I just like typed 4 lines and erased it. I'm just gonna continue reading into this Banks 1&2 stuff and its relation to the 2 precat O2s. We mite just have to agree to disagree. :cheers: :thumb3:

I can't believe others aren't chimming in.

 

[JayRolla]

ODB1 so much easier, I would just get a wbo2, wire in, simulate narrowbands o2 to ecu, call it good. Then convert to speed density. Dead on tune all the time. I love all the reading, its been years since I have tuned anything and its hard to remember all this stuff. I really just know how to get car to go fast safe. All this fuel trim talk making my head spin. LOL. We never cared about fuel mileage on those cars.

 

[gamefreakgc]

:redbrick: That is so weird. Ok help me clarify. You have the 3400 correct? And I assume you have 4 O2s? Ok, I just like typed 4 lines and erased it. I'm just gonna continue reading into this Banks 1&2 stuff and its relation to the 2 precat O2s. We mite just have to agree to disagree. :cheers: :thumb3:

I can't believe others aren't chimming in.

Sorry, I don't think I was very clear on one of those posts. There's only two O2 sensors, but some rigs have two cats. Mine only has one cat and two O2 sensors. California emission rigs have two cats and two O2 sensors.

However, the system labels the O2's as Bank 1 Sensor 1, and Bank 1 Sensor 2. There's no O2 sensors associated with Bank 2. If it doesn't make much sense, that's ok because it's really confusing.

 

[gamefreakgc]

ODB1 so much easier, I would just get a wbo2, wire in, simulate narrowbands o2 to ecu, call it good. Then convert to speed density. Dead on tune all the time. I love all the reading, its been years since I have tuned anything and its hard to remember all this stuff. I really just know how to get car to go fast safe. All this fuel trim talk making my head spin. LOL. We never cared about fuel mileage on those cars.

Haha, yeah. Only downside is that trying to figure out check engine lights is a PAIN! I had a code 25 (lean) on my pickup for about 2 years. Now that I'm driving it again the code has come back. I've swapped out pretty much every part in the engine trying to fix it to no avail since the codes are so vague. I'm just running till it dies at this point.

Trying to save MPG's is kind of a lost cause on a 4Runner. Even getting 20 MPG's on these would be miraculous and it's pitiful compared to V6's Toyota and others are making these days. Our ECU doesn't take to tuning all too well though, it's so basic. You have to wire up a piggyback in order to actually do anything.

 

[Robb235]

Bank 2 is the exhaust leaving your converter. This is sort of the "smog pass" sensor that will detect high HC or O2 readings in your gas. If it reads high HC (fuel) for example, it will decrease the fuel at the injector to compensate. Or the opposite if it reads high O2. This is why I brought up the Bank vs. LTFT readings since the two are similar. Those of us with OBD-I vehicles can sometimes get blindsided with repairs for not passing smog, since we do not have a O2 sensor after the cat. Those with OBD-II vehicles normally do not have this issue, due to the second O2 sensor always monitoring the exhaust gases. Basically though, you can't get good readings off the rear one other than to determine if your cat is failing or not.

I disagree with this part. The downstream O2 sensor has no effect on fuel trims. It's only purpose in life is to determine if you catalytic converter is working, and if it it's not, it throws a code. On California Emissions 4Runners (ones like mine that have 2 catalytic converters), the rear O2 sensor is periodically used by the ECU to recalibrate the front O2 sensor.

 

[Skinfaxi]

Yikes. There is a lot of misinformation in this thread. Some of you are correct. Bank1/2 refers to the left & right side of the engine, fed by the front O2 sensors. The rear O2 sensors are used for the catalyst efficiency monitor. On a 4 cylinder, it either refers to the front 2 and rear 2 cylinders, depending on how it is routed, or more commonly the bank 2 codes are disabled (p0174 etc.) Again, the rear O2 is just to monitor the cat.

Someone mentioned if the air/fuel is suspect on an individual cylinder, a code will set for that cylinder. That is incorrect. EPA started phasing in A/F Imbalance Monitor requirements in the '13 model year, set to finish in the '16 model year. Even then, the OEMs are struggling to make it work properly. 3rd gen 4Runners definitely don't have the capability to detect individual cylinders.

Fuel trims are supposed to move quite a bit. People chase fuel trims assuming something is wrong with their car, while simply the difference between winter & summer fuel blends will account for a 10% swing or more (the primary force behind how fuel trims are calibrated by the OEMs.)

If you're setting a code, start investigating. If not setting a code, the car is doing what it's supposed to.


Source - I'm an OBD calibrator for an OEM.

 

[JayRolla]

Love this last post. Thanks for info. This makes more sense. I have been saying from beginning his car running fine. It's when it's pegged and throws cel when you have an issue. This 14% adjustment just means his car is working to get good fuel mileage. He needs not to worry about the trim when it's within its range.

 

[Skinfaxi]

Love this last post. Thanks for info. This makes more sense. I have been saying from beginning his car running fine. It's when it's pegged and throws cel when you have an issue. This 14% adjustment just means his car is working to get good fuel mileage. He needs not to worry about the trim when it's within its range.

Yep, there's a reason the owner's manual doesn't mention fuel trims. They'd get way too many people coming into the dealer thinking their car is messed up because the trims are moving.

It's the same reason the coolant temp is a needle with a HUGE dead zone, and not a real-time number. It'd freak people out.

 

[gamefreakgc]

Yep, there's a reason the owner's manual doesn't mention fuel trims. They'd get way too many people coming into the dealer thinking their car is messed up because the trims are moving.

It's the same reason the coolant temp is a needle with a HUGE dead zone, and not a real-time number. It'd freak people out.

I just wish our fuel gauge needle was a bit more accurate! I have about 5 gallons left when my gas light turns on lol...

 

[Robb235]

I just wish our fuel gauge needle was a bit more accurate! I have about 5 gallons left when my gas light turns on lol...

And how often do you see a 4Runner on the side of the road because the owner accidentally ran out of gas? Lol.

 

[Skinfaxi]

I just wish our fuel gauge needle was a bit more accurate! I have about 5 gallons left when my gas light turns on lol...

I gave up & bought a scangauge almost exclusively for a distance to empty display. If you calibrate it properly, it's extremely accurate.

 

[tlib99]

Hey Skinfaxi, thanks for your input. I guess I wasn't completely wrong. So am I understanding you correctly? If the LTFT is consistently high this is normal? So when the info world says the normal range is +/- 10 is normal anything high is suspect for a situation. I understand it could go above that for a minute or two and that's not a sign of an issue. But if its constantly that high is that still normal. I understand that the LTFTs job is to keep the STFT as close to zero, correct? Anyway, sorry for asking questions, it's just how we learn, yea?

For example, I just got done changing my intake gasket on my silverado, and before, my LTFT's was at 24% at idle, now they are back to zero, yes had a vacuum leak. So is it just coincidence to achieve near 0, LTFT? And so different vehicles have different "normal" fuel trim ranges? I dont know, this stuff makes my head hurt, but I sure do enjoy learning.

 

[Skinfaxi]

Hey Skinfaxi, thanks for your input. I guess I wasn't completely wrong. So am I understanding you correctly? If the LTFT is consistently high this is normal? So when the info world says the normal range is +/- 10 is normal anything high is suspect for a situation. I understand it could go above that for a minute or two and that's not a sign of an issue. But if its constantly that high is that still normal. I understand that the LTFTs job is to keep the STFT as close to zero, correct? Anyway, sorry for asking questions, it's just how we learn, yea?

For example, I just got done changing my intake gasket on my silverado, and before, my LTFT's was at 24% at idle, now they are back to zero, yes had a vacuum leak. So is it just coincidence to achieve near 0, LTFT? And so different vehicles have different "normal" fuel trim ranges? I dont know, this stuff makes my head hurt, but I sure do enjoy learning.

Being close to zero is good, but not more or less "correct" than say 10%. Being at zero basically means you're running very similar conditions to what the engineers had when they decided where zero should be (fuel blend, atmospheric conditions, etc.) We perform extensive testing to make sure that fuel trims will adapt to the different types of gasoline found all over the country. Factor in combustion properties that change with air temperature, humidity, elevation, etc. and things get hairy. As long as none of your trims are maxed out to the point that a code sets, then you're in a range that the engineers considered normal based on what they saw in prototype development of the vehicle. Not only are trims intended for compensating for different fuel blends, but also for non-perfect engine calibrations (temperature compensation for manifold filling, torque modelling, etc.) They're really handy for smoothing out feed-forward performance, or anticipating how much fuel you need quicker than the O2 sensors can react. A perfect engine calibration would eliminate the need for trims, but that's realistically impossible, too much money & resources. Instead, fuel trim software takes over and soaks up the error in the maps.

At the end of the day, fuel trim behavior for a particular model is typically decided by a couple guys who said something like "Fuel trims? Yeah I think they're working OK. Lock it down & ship it." I guess some customers think it's more of an exact science than it really is, so they get concerned when they see trims moving. It's normal!

Oh, and I don't have the software code for the 4Runners, but I bet you they have fuel trims for different volumetric air masses, as do most cars, but it only reports the active cell over CAN. With this behavior, you'll see the displayed fuel trims change rapidly as engine load changes (it's sweeping across the learned trim cells.) That explains the behavior mentioned in the first post. Perfectly normal.

 

[Andrewjeffrey]

From previous experience and from Youtube, I have learnt that this problem is due to the IAC Valve being defective. It is NOT normal for the fuel trim readings to increase on acceleration.