So I'm dealing with a 4.2l from 2000. I've got codes-

0174 Lean
0171 Lean
0156 Problem with B2 S2 O2
0303 misfire
0301 misfire

I took some fuel trim readings while it was running. It is not running well. It keeps going into OL-Fault and CL-Fault. I show B1 STFT going to -20 while the others read 25 or 32. I'm still trying to make headsor tails of some of these readings, but I know that that reading is different from the others. Different sensor than my 0156 code too.

Any thoughts? I just bought my first Live Data code reader so I am trying to learn how to use the live data for diagnosis. Part of me just wants to change all four O2 sensors. The vehicle has about 150k on it.

 

Vacuum leak. Fix it first, reset the PCM, and see what's left and go from there.

Steve

 

Vacuum leak? How certain do those codes make you think that? Only reason I ask I because I did do some checking and I tried spraying carb cleaner around and it didn't change the idle. I didn't spray while checking fuel trims, so it still could have had an effect, but not enough that I could hear a difference.

I'll admit that I was beginning to think it was the 02 sensors.

What is the life of an O2 sensor on these trucks/vans?

 

check for a leak between the air cleaner and the throttle body...unmetered air will affect fuel trim

Mark

 

Well, when I get a chance to look at the engine, I'll be checking for the vacuum leaks again.

Still wondering-

Life span of an O2 sensor?

What should be fuel trims typically read? What would incorrect readings look like/what would they mean?

 

Your O2 sensor is fine, they should last in excess of 100,000 miles or double that if regular maintenance is kept up. The first two codes indicate a vacuum leak prior to the throttle body. Then you have a couple of misfire codes too. Get these things taken care of and the O2 code will likely be fixed too. Good luck!

 

You should be able to answer your own question, but if you're set on replacing your 02s have at it. AutoZone makes big bucks selling 02s when people come in and they read P0171 or P0174 for them. If DTC P0171 or P0174 goes set what does that mean? If the PCM gives you either one of those DTCs based upon information coming from the 02s are the 02s working or not? Are you a parts changer or a troubleshooter? If you change all the parts in your engine one at a time you will eventually fix this problem. Is that your method? If you solve the lean DTCs you may find the others are phantoms.

 

OK, I think we're getting somewhere. Though I'd still love to have someone fill me in on Live Data info, or link me to where I could learn some.

What about dirty MAF sensor? Only reason I ask is because I spent a good while on this car trying to find vacuum leaks. (And since I didn't mention, it's not my vehicle, so I only get to look at it every now and then to help out.) Like I mentioned, I sprayed carb cleaner all around and didn't have any changes.

So my next steps once I get to work on this again-

-Check for vacuum leaks again
-Clean MAF
-???

 

Ah, and I don't know when the last time they changed the fuel filter was...

 

Ok, I cleared the codes, changed the fuel filter, cleaned the MAF, and it still seems to have the same problems.

I noticed that either my B1 STFT or B1 LTFT readings always seem a bit off. I tried spraying carb cleaner around and I didn't notice much of an idle change, but I did get the B1 O2 sensor reading to move around by spraying. My only problem is that I cannot tell exactly where spraying causes it. It is on an E150 and I don't have a very clear shot, but it might be the intake manifold. Is there a good way to make sure it is a manifold gasket leak before I start tearing it apart?

 

Can you have someone watch your STFTs closely while you spray. I'd use a piece of cardboard behind the fan to temporarily block it from blowing the spray all over the place during the test. You can try a long nozzle on the spray can or bottle to concentrate the spray in a specific spot. As soon as the STFTs move RICH make not of that area. You'd rather find a cracked rubber hose than a leaking intake manifold gasket.

 

use a long piece of vacuum hose so you can get an exact location

Mark

 

What should the STFTs typically read? I saw mine drop from about 25 to 14 when I was spraying.

 

"Typically"? There is no such thing. Each vehicle is different. Ideally might be a better word. "0" for STFT and "0" for LTFT would be perfect, but no vehicle reads that value even off the assembly line. The numbers you gave are either a % or a power of 2 from 0 to 255 with 0 being fully lean and 255 being fully rich and 128 being perfect which is equal to "0%". You didn't provide enough info to figure that out. Are the numbers you provided a % and if they are they must have a POS or NEG designator OR are they binary numbers from 0 to 255? If they are a percentage it is either positive(Rich) or Negative(Lean) depending on whether there is a POS(+) or NEG(-) designator. If it is an integer than they are both at the EXTREME end of the Lean side(not likely). The binary scale for fuel trims runs from 0 to 255 with 0 being all the way lean and 255 being fully rich and 128 being equal to "0" which is a perfect value for a fuel trim. These values depend on what scan tool you are using. The user manual for your scan tool should have provided this info to you.

 

Ok, mine are percentages. I've got three sensors reading 25-32% and then one that seems to continually drop into the -25 range. That'd be the B1 STFT, I believe.

When I was spraying around yesterday I only noticed the numbers change on the B1 sensors, I am guessing I should pinpoint my search to Bank 1.

Also, if I didn't mention, after clearing my codes, the first two to pop up were misfires on cylinder 1 and cylinder 4.

I hope this can help you guys help me...

[I just wanted to insert this... just because...]