had exhaust done, lean O2 reading

[Neverdie38]

99 Expy XLT 4.6L, i had someone cut both of my rear cats off and just weld straight pipe in with my O2 sensors in it, hoping to increase exhaust flow. now getting a bank 1 lean O2 reading. just wondering if he placed the O2 sensor too far back or if the cat helped it read correct. can anyone tell me the distance between the 1st cat and the 2nd oxygen sensor for each bank? would be much appreciated so i can try to help my mpg. please and thank you

 

[joezek]

I don't know the distance for the second O2 sensor but I do have an opinion on the problem. Cutting the second cat off should cause the exact problem your having, if it's really flowing that much more exhaust. Moving the rear O2 sensor shouldn't have any effect on a lean problem. The second sensor should only have the purpose of checking whether or not the forward Cat is working or not. The second O2 sensor doesn't control the fuel mixture.

Removing the second Cat caused less back pressure, faster flowing exhaust, and a cooler O2 sensor. If it's beyond the standard range of regular fuel curve then you probably get the CEL no matter what.

Since only one side did it you might be able to fix the problem by replacing the forward O2 sensor with a new one. Your old one might be slow/lazy and not reporting the proper information to the computer.

Try swapping the left/right forward O2 sensors and see if the problem moves to the other side.

 

[Racenut]

I have done the rear cat delete on my '02 EB and have never had the CEL come on for a " lean condition ". I would have to agree with JOEZEK in that I belive it would be a problem with your o2 sensor and not the placement or the cat removal.

The main codes that the rear o2 sensor would set are :

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

P0430 Catalyst System Efficiency Below Threshold (Bank 2)

These codes tell you that you basically do not have enough flow, or that there is no change in the exhuast gas levels between the Front o2 and the Rear o2.

The rear o2 sensors can also set these codes :

P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)
P0137 02 Sensor Circuit Low Voltage (Bank I Sensor 2)
P0138 02 Sensor Circuit High Voltage (Bank I Sensor 2)
P0139 02 Sensor Circuit Slow Response (Bank 1 Sensor 2)
P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0156 02 Sensor Circuit Malfunction (Bank 2 Sensor 2)
P0157 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
P0158 02 Sensor Circuit High Voltage (Bank 2 Sensor 2)
P0159 02 Sensor Circuit Slow Response (Bank 2 Sensor 2)
P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)


Here is the code I am guessing that you are seeing :

P0171 System too Lean (Bank 1)

Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.

Symptoms

You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.

Causes

A code P0171 may mean that one or more of the following has happened:

•The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.

•There could be a vacuum leak downstream of the MAF sensor.
Possible SolutionsPossible solutions include:

•In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling

•Inspect all vacuum and PCV hoses, replace if necessary

•Check for a dirty fuel filter and proper fuel pressure

Hope this helps ya out a bit .

 

[Neverdie38]

i was getting the P0420 code. i took the "below threshold" as it was reading lean. would that mean my front sensor is reading bad or do you think the 2nd cat made too much flow?

 

[Racenut]

i was getting the P0420 code. i took the "below threshold" as it was reading lean. would that mean my front sensor is reading bad or do you think the 2nd cat made too much flow?

That code usually means that your front cat is going bad.

It is comon on these trucks and basically the second cat was hiding the problem.

You have a couple of ways you can go about fixing the issue :

1. Replace the front cats with new ones and leave the rear off.

2. Put the rear cats back on and remove the front cats.

3. Instead of dealing with the stock style cats, take out all of the cats and put 1 high flow cat on each side in between the o2 sensors.

Out of these three options, I would personally advise to go with either option 1 or 3. If you put the rear USED cats back on you may eventually run into the same problem. So instead of cutting and welding over and over just put in 2 new cats ( one on each side ) and be done with it.

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

What does that mean?

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms

You will likely not notice any drivability problems, although there may be symptoms.

Causes

A code P0420 may mean that one or more of the following has happened:

•Leaded fuel was used where unleaded was called for

•An oxygen sensor is not reading (functioning) properly

•The engine coolant temperature sensor is not working properly

•Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe

•Retarded spark timing

•The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible SolutionsSome suggested steps for troubleshooting a P0420 error code include:

•Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.

•Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).

•Inspect the downstream heated oxygen sensor (HO2), replace if necessary

•Replace the catalytic converter

 

[Neverdie38]

im thinkin of option 3. thanks for the info. what high flow cat would you recommend?

 

[Racenut]

im thinkin of option 3. thanks for the info. what high flow cat would you recommend?

Any of them that are by a reputable company. Stay away from china junk!

 

[Fanatic1074]

One question, did you happen to try resetting the ECU? Disconnect the Negative cable and let it sit overnight. This will reset everything and the O2 sensors should adjust to the new flow.

 

[Fanatic1074]

Double post, sorry.

 

[joezek]

Any new news? Is the problem fixed yet?

I just did my exhaust system a few days ago and haven't had any CEL yet. I removed both rear catalytic converters, ran two separate pipes back to a dual inlet muffler. I'm guessing you just have an O2 sensor that's ready to be replaced.