Lean Bank1 and Bank 2

[solidaxel]

Well we have a code that will not stay clear until I fix the problem !

We are at some times in the AM when first start a small backfire, but it only does it once

What is the cause of the lean Bank 1&2 and how do I correct it?

[A8Jamesa8]

Fuel System Too Lean (Bank 1 or 2)

Our emissions expert has put together the following information about the P0171 and P0174 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

OBD II P0171
OBD II P0174
Fault Code Definition

OBD II P0171 Fuel System Too Lean (Bank 1)
OBD II P0174 Fuel System Too Lean (Bank 2)
Symptoms

Check Engine Light will illuminate
In some cases, no adverse conditions may be noticed by the driver
In other cases, there may be performance problems, such as a lack of power on acceleration and some "coughing" or misfiring
The vehicle may have trouble idling, especially when warm or when sitting at a stoplight
Common Problems That Trigger the P0171 and P0174 Code

PCM software needs to be updated
Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
Mass Airflow Sensor (MAF)
Plugged Fuel Filter or weak Fuel Pump
Plugged or dirty Fuel Injectors
Common Misdiagnosis

Oxygen Sensors
Polluting Gases Expelled

NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
The Basics
Combustion engines operate by burning an air/fuel mixture of about 14.7 to 1—14.7 parts air to 1 part fuel. When the air ratio goes below 14.7 parts, this is called a "rich" mixture. If the air rises above 14.7 parts, it is called a "lean" mixture.

Rich Mixture = Too much fuel, not enough air
Lean Mixture = Too much air, not enough fuel

To keep the engine running properly, the Engine Control Module measures the oxygen content in the exhaust with oxygen sensors and makes adjustments to the mixture by injecting more or less fuel.

The control module operates within specific parameters and under normal conditions, it will make minor adjustments to the air/fuel mixture. When these adjustments become too large, a fault code is set. When the P0171/P0174 code sets, the oxygen sensors are detecting too little oxygen in the exhaust and the control module is adding more fuel than normal to sustain the proper air/fuel mixture.

P0171/P0174 Diagnostic Theory for Shops and Technicians
When a vehicle has the fault code P0171 and or P0174, it means that computer can no longer automatically adjust the mixture between air and fuel. Code P0171 applies to Bank 1 and P0174 applies to Bank 2. Code P0174 mainly applies to V6 or V8 engines because 4-cylinder engines generally have only one bank, though there are a few exceptions. Some of the high performance 4-cylinder and straight 6-cylinder engines (such as those in BMW and Lexus) split the cylinders into groups of two or three and call them separate banks.

When the code says that the Fuel System is "too lean," it means that the computer has been adding more and more fuel, which is called Long Term Fuel Trim. Ideally, the Long Term Fuel Trim should be close to 1 to 2 percent. When a code P0171 is set, it means that the Fuel Trim is anywhere from 15 percent to as high as 35 percent compensated. When this happens, the computer knows that there is an improper condition in the control of the Fuel System.

The first step in the diagnosis of a code P0171 and/or P0174 is to look at a minimum of three ranges of the Long Term Fuel Trim numbers on a scanner. Check the idle reading—3000 RPM unloaded and 3000 RPM with at least 50 percent load. Then check the freeze frame information for the code to see which range(s) failed and what the operating conditions were.

Before we get into the main causes of P0171, let's explore why this code matters.

Why Does a P0171/P0174 Code and Running "Too Lean" Matter?
"Lean" running cars and light trucks are highly polluting vehicles. Most of the NOx pollution, which is poisonous and can cause asthma, is caused by vehicles that are running too lean. A lean running car can also misfire, which puts raw fuel (HCs) into the atmosphere. When you are behind a car or truck that smells bad and makes your eyes burn, it is misfiring and running too lean. In comparison, a "rich" running engine has no smell (CO is odorless) or you may detect a rotten egg smell, which is caused by the Catalytic Converter consuming too much sulfur, like when you are behind a big SUV at full throttle going up a long, steep hill.

P0171 is not an Oxygen Sensor problem. Before a P0171 code is possible, the computer first ran a series of tests to validate the readings from the oxygen sensors. Since the oxygen sensors passed their readiness tests and didn't set any codes, the computer then looked to the Fuel Trim adjustment. When the computer determined the air-to-fuel mixture to be too lean, it then set the P0171 code.

What Are Some Common Causes of Code P0171/P0174?
Always check to make sure that there is not a PCM software update due or available. Often, as the vehicle's engine wears, the PCM's Fuel Map software inaccurately compensates for this condition. The fuel mixture grows lean and eventually, the code sets.

A vacuum leak is very common. It could be a torn PCV hose, a torn Intake Air Boot, or even a broken seal on the dipstick (the dipstick is a part of the PCV system and if it does not seal, too much unmetered air will enter the engine). Don’t rule out a sticking/leaking EGR Valve or leaking EGR or Intake Manifold Gasket. If it is a V6 or V8 engine and the code is only on one side/bank, it could be a defective Intake Manifold Gasket or cracked/leaking manifold.

What if There Is No Vacuum Leak or Both Codes (P0171 and P0174) Set?
An "under reporting" Mass Air Flow Sensor can be a common cause of a code P0171 and P0174. Essentially, this means that the Air Flow Sensor is telling the computer that much less air is entering the engine than actually is.

Since the oxygen sensors are telling the computer that more fuel is needed, this causes confusion in the computer because the Mass Air Flow Sensor is still saying there is too little air and the Oxygen Sensor is reporting that the mixture is still too lean. The computer tried to compensate, but since resolution is impossible, it sets the code. It is important to restate that the Oxygen Sensors are accurate—the fuel mixture is too lean. In this case, the Air Flow Meter or Sensor is inaccurately reporting the real amount of air entering the engine.

How Do I Know if the Problem Is the Mass Air Flow Sensor?
There is a very effective "truth test" for any Mass Air Flow Sensor. Start the engine, let it idle, and then check the Barometric Pressure reading on the scan tool data. If the reading is about 26.5 Hg and you are close to sea level, you know that you have a defective Air Flow Meter because it is telling you that you are at about 4500 feet above sea level. (These conversion tables will help.) When the Mass Air Flow Sensor sees this Barometric reading, it adjusts its Air Density table and then "under reports" the actual amount of air entering the engine. It does this because the Barometric Pressure Sensor is actually part of the Mass Air Flow Sensor.

Sometimes the Air Flow Sensor and the sensing wire get covered with dirt, dust, or oil residue, which can also set a P0171. Cleaning the sensor might hold off problems for a while, but eventually, the MAF sensor should be replaced. Always make sure the Air Filter and its enclosure are dirt-, dust-, and oil-free. If you clean and replace the filter and its enclosure as needed, you will prevent the new MAF from failing.

Additional Causes of Code P0171/P0174

A plugged Fuel Filter or poorly functioning Fuel Pump can set the P0171 code. The computer hears (accurately) from the Oxygen Sensor that the Fuel Mixture is too lean so the computer keeps increasing the amount of fuel being delivered into the combustion chambers. But in this case, the Fuel System can’t increase the amount of fuel.
If you still can't find the problem, be sure to check and verify that fuel pressure and delivery are at spec. If fuel pressure and volume check out okay, scope the injectors and perform injector drop and/or flow tests to see if they are capable of delivering enough fuel. Dirty/contaminated gas can definitely plug injectors and trigger these lean codes.

[A8Jamesa8]

I threw a p0174 and I cleaned my MAF sensor with MAF sensor cleaner that I bought from the local auto parts store and it seemed to do the trick just follow the instructions on the can and be very carful not to touch the MAF elements they are extremely fragile.

Have not had the CEL light back since.

[ls1nova71]

First off, do you have adequate fuel pressure? If not fix that first. But on a lot of swaps if the engine has been sitting for a while the injectors will stick due to the crappy gas we have now days. I would try cleaning them and see if it helps. Sometimes just running some ffuel injector cleaner in the tank and driving it will help.

[Nochance]

The most common problems are dirty MAF sensor, and vacuum leaks. Since you have codes for both banks it will usually be something that affects both banks. Look for air leaks between MAF and t-body and the other common leak is intake gaskets that only leak when engine is cold once the engine heats up the intake gaskets swell and seal leak.

[solidaxel]

T just typed a 4 paragraph and attached pic and it deleted it all !!
Later when I have some more time I will reply

Thanks for the help

[solidaxel]

Thanks for all the help and suggestions.

O K, I checked a few items today;

Vacuum at idle is 18"
fuel pressure is 52#
Fuel system is all new
Intake and injectors have been cleaned and flow tested
I swapped the MAF with my 78 with the LM4
The air filter is a K&N in a air box in front of the radiator
The truck runs good and starts fine.
I did test the brake booster and it is holding vacuum, but only about 5#

[BR3W CITY]

Does that fuel pressure fluctuate at all? If your not on a flex fuel motor, 52 is just a little low...but keep in mind that could be margin of error on the gauge. In general, I'd consider it acceptable, unless under load it drops any more than that.

[solidaxel]

I will check tomorrow, and watch the gauge, are you thinking maybe the Fuel pressure reg.?

[BR3W CITY]

Potentially, yes. Its just such an easy culprit in multi-bank lean codes.

[solidaxel]

I looked at a FPR 17113700 is this the right Regulator for this 5.3 2003, or is there a better one?

[TooTall]

What year engine, and is the fuel system a return or return-less?

If both banks are lean, it can be the FPR on the return system. This will be at 58-60 psi all day long no matter what throttle position.

If it's a return-less system, then it's the intake gaskets. The orange style gaskets are known for leaking. The newer ones are green, and you can get the A/C Delco or Felpro brands. It's an easy job.


really clean looking intake pluming !

[solidaxel]

The engine is a 2003 Tahoe 5.3 and it is a return type fuel system

[not2oldchevy]

Originally Posted by solidaxel

The engine is a 2003 Tahoe 5.3 and it is a return type fuel system

I have the same engine 52 pounds is all the pressure that engine runs. You would have to change the fuel rail to get a fpr that will hold more pressure. That 2003 is made to run on 52 pounds.

[BR3W CITY]

Originally Posted by not2oldchevy

I have the same engine 52 pounds is all the pressure that engine runs. You would have to change the fuel rail to get a fpr that will hold more pressure. That 2003 is made to run on 52 pounds.

Unless its flex fuel, no. Return or returnless, they all ran the 58-62 rail pressure. Only the Flex fuel trucks (metal rail) ran the lower pressure. In 2003 you could get a plastic return rail, a metal flex fuel rail, or if it was a late-production run you could get the returnless plastic rail.

[not2oldchevy]

Originally Posted by BR3W CITY

Unless its flex fuel, no. Return or returnless, they all ran the 58-62 rail pressure. Only the Flex fuel trucks (metal rail) ran the lower pressure. In 2003 you could get a plastic return rail, a metal flex fuel rail, or if it was a late-production run you could get the returnless plastic rail.

The only fpr that will fit a 2003 return system will only do 52 pounds pressure.

[ls1nova71]

Originally Posted by BR3W CITY

Unless its flex fuel, no. Return or returnless, they all ran the 58-62 rail pressure. Only the Flex fuel trucks (metal rail) ran the lower pressure. In 2003 you could get a plastic return rail, a metal flex fuel rail, or if it was a late-production run you could get the returnless plastic rail.

Originally Posted by not2oldchevy

The only fpr that will fit a 2003 return system will only do 52 pounds pressure.

Not to play Devil's advocate, but there are a couple different flex fuel rails, but they are not all metal. Some are plastic and look just like the non flex, which is probably what not2oldchevy has. They are distinguishable by where the vacuum port is on them. Flex fuel rails will have the port in the center of the side of the regulator where as the non flex will come out of the top. Here are two pics, the one in my truck is a non flex, the one sitting on the hood is a 2003 flex fuel rail. You cannot switch the regulators from flex to non flex, they are completely different, trust me, I tried!

[BR3W CITY]

Originally Posted by not2oldchevy

The only fpr that will fit a 2003 return system will only do 52 pounds pressure.

No. The only reason I'm drawing a hard line is that I can walk out to the garage and show you a 2003 Lq4 with a return style system (stock), and then show you my video on that exact setup running 58-60 PSI on the gauge.

Here my exact motor, on the 2003 rail, with over 58psi. Feel free to tell me the gauge is wrong or that it isn't a 2003

You Tube

LS1Nova, is the plastic FF rail common at all? I've sourced a decent number of motors and don't think I ran into any off the top of my head that had plastic rails. Is there any other identifying mark? It looks JUST like the regular truck rail.

[TooTall]

Originally Posted by solidaxel

The engine is a 2003 Tahoe 5.3 and it is a return type fuel system

pull the intake, and swap out the manifold gaskets

[solidaxel]

The first pic looks like the one we have

[ls1nova71]

Originally Posted by solidaxel

The first pic looks like the one we have

Then you have a flex fuel rail and 50ish PSI is all youre going to get out of it. You need to have your engine tuned for flex fuel injectors, if it has a regular tune then this could be your problem.

[solidaxel]

Originally Posted by solidaxel

The first pic looks like the one we have

The only difference is the color of the fuel log, ours is silver if that makes any difference!!

[ls1nova71]

Originally Posted by solidaxel

The only difference is the color of the fuel log, ours is silver if that makes any difference!!

The flex fuel rails have the silver fuel lines, non flex are black. In the picture I posted the lines are switched, I wanted the silver lines for my truck, and after finding out the regulators wouldn't interchange, I swapped the lines.

[BR3W CITY]

Solidaxel - If it is in fact a flex rail, and your running a standard tune, bingo.
You won't be able to actually run it as flex fuel unless you add the fuel sensors, but you can still run it on gas just fine.

[solidaxel]

I will have my tuner look into which fuel system the ECU is programed to.
I did remove the ECU from my 78 which is the same year 5.3 and swapped them.
The 78 does not show any codes and the ECU in the 46 now is still showing codes Lean 1 & 2
I am leaning towards the FPR OR the intake gaskets.
I will do some more troubleshooting next week when we change parts and spray the intake with carb cleaner and look for RPM increase
Thanks folks for your help, we will get to the cause!