P0171 - System Too Lean

[Th0r]

I just had this code pop up today.

Things to note:
AFR doesn't seem lean. Idle is normal and WOT reads 11.X on the Tech2.
I've tested for vacuum leaks with carb cleaner. None.
Bank 1 O2 was replaced with a heated sensor about 3k miles ago.
I found a P1171 - Fuel System Lean During Acceleration in history.
There is alot of oil on the breather filter for my PCV.

Any ideas on what I can do or check next?

[[ion] C2]

Wideband O2?

[Th0r]

Nope. Nothing spliced.

[[ion] C2]

No I mean do you have a wideband O2 or is this "Tech II" just reading the narrowband?

[BlackJack]

given that it's lean "under acceleration" could mean at any throttle position between 5% (less than 5% is considered idle) and 100% (98%+ is WOT).

That's a wide range to cover. What tuning device are you using? (not scanning device)

[Th0r]

Oh. Yes, the heated sensor is a Bosch wideband.

All I have is a Tech2.

[Th0r]

Also, the car is for sure running rich as hell now. The exaust smells like raw fuel and the back bumper around the outlet is covered in soot.

[BlackJack]

sounds like an injector that may be sticking open. Hard to tell without some hands-on troubleshooting.

[clutch1]

Plug the PCV and see if it gets better.. if there's a lot of oil in there it might be stuck open.

Also... try smoking the system to check for vacuum leaks, works MUCH better than carb cleaner I've found.. find a buddy with a smoke machine.

[Alerojester]

or a fog machine?

[clutch1]

If you can get the fog to come out of a little tube, yea, that'd be a good idea. Just pump it into the brake booster hose or something, that's usually where I go.

[[ion] C2]

Plug the PCV and see if it gets better.. if there's a lot of oil in there it might be stuck open.
Psst... this is an LD9. Ignore clutch1's comment. The PCV hose that comes off the baffle is always going to be oily or oiling up the breather you stick on it, don't worry about it.

Also... try smoking the system to check for vacuum leaks, works MUCH better than carb cleaner I've found.. find a buddy with a smoke machine
No, hook up a low pressure air line to your throttle body and do a boost leak test. You just listen for hissing with the car off. That is THE best way to find a vacuum leak and extremely quick and simple.

Bank 1 O2 was replaced with a heated sensor about 3k miles ago.
Oh. Yes, the heated sensor is a Bosch wideband.
So you're saying you replaced the factory narrowband sensor with a wideband? There's one insanely huge problem. But if that were true you'd've noticed this issue when it was first installed, because you can't just replace it outright without any additional modification.

[clutch1]

C2;531725']Psst... this is an LD9. Ignore clutch1's comment. The PCV hose that comes off the baffle is always going to be oily or oiling up the breather you stick on it, don't worry about it.


No, hook up a low pressure air line to your throttle body and do a boost leak test. You just listen for hissing with the car off. That is THE best way to find a vacuum leak and extremely quick and simple.



So you're saying you replaced the factory narrowband sensor with a wideband? There's one insanely huge problem. But if that were true you'd've noticed this issue when it was first installed, because you can't just replace it outright without any additional modification.

Sorry I don't know the intricacies of the LD9. I know a stuck open PCV sucks more oil in than normal and acts as a vacuum leak to a degree (lean running)

Smoke is MUCH better than just air, because you can only feel/hear air. The smoke machine I use pumps in pressurized smoke and you don't have to listen or do much of anything, just look where it comes out.

You CAN replace the factory o2 sensor with a wideband. Certain ones have two signal wires, one with the wideband scale and another that reads the traditional 0v-1v range the ECU likes.
I don't know if the Bosch is one like that.. but as long as it's getting it's proper signal it'll be happy.

Plus I don't see how getting to high of a signal would throw a lean code. If the proper A/F mixture shows up as .5 on a narrow and 2.5 on a wide, the signal would be muuuuch higher than the computer wants to see, and would think it's running nasty rich based on the signal voltage.

[[ion] C2]

Except our PCV system isn't hooked up to vacuum. It's just a baffle that vents to air or the air intake.

Pressurized smoke would be the best, I agree. Didn't know it was pressurized. I think of a fog machine at parties when you talk of hooking one up.

You can replace it with the wideband but most people don't have the proper setup. I have a BOSCH wideband from AEM and you can't use it as a narrowband and a wideband at the same time. It has a narrowband simulation mode though.

[clutch1]

Ooo, is it one without a valve.. one of those oil separator screen setups?

Yeah, the smoke machine is amazing.. it's one of these:
http://www.denlorstools.com/shop/images/OTC-6521-lg.jpg

Plus the stuff that comes out smells real good lmao.

Ah, then if the Bosch only has the wideband signal, yea, change that crap to an OEM o2s... no reason to have a wideband on a stock car anyways.

[comanche]

Do you have access to a graphing scan tool?

Like a Modis?

I'd be interested in seeing:
1. Oxygen sensor graphs
2. Short term/ long term fuel trim numbers

Do you have those available?

[Th0r]

At idle and cruise ST Fuel Trim sits at a steady 49%. LT Trim is 18%. I'll see if I can pull anything on the O2s.

[comanche]

Wow.

Crazy fuel trim numbers!

Hmm
If a sensor is stuck lean (can tell from graph prolly) then maybe that is causing the rich run?

[Th0r]

I had no way of getting a graph. I did narrow it down to the pos1 O2 sensor. I had installed a heated sensor to solve the following issues codes:
P0130 - Circuit Closed Loop (CL) Performance Sensor 1
P0133 - Slow Response Sensor 1
I ran the heated 02 for almost 5k miles with no issues till now when it threw the lean codes. I unhooked the heater lines to the sensor and the car is running perfect again, but the O2 codes are back now. If plug the heater wires back in I throw lean codes in a matter of minutes. I had it at a shop for a couple days and none of the techs had any luck figuring it out. Bah.

[comanche]

Someone correct me if I'm wrong.... maybe a major exhaust leak?

If there was a major exhaust leak after the engine, before the O2 sensor...
-Oxygen sensor would see much a much leaner mixture... since there would be a greater percentage of oxygen vs hydrocarbons...
-PCM will throw more fuel at the engine to make the mixture correct.... giving you those fuel trim numbers... and causing the car to run quite rich... but the car would think it was still running okay...

Anybody else think this might make sense?
Bad exhaust manifold gasket, or crack in manifold, or hole in exhaust?

Edit: BTW, you are going to kill the converter if you keep driving it this way...

[Th0r]

I'll check the header gasket. It is copper so there is a chance it would need retorqued, but I certainly don't hear anything. I'll plug the tailpipe and hook an air line into an O2 bung and to if I can hear any leaks.

The more I think about it the more I think the issue isn't with the O2. The fact that the slow response codes came back as soon as I unplugged the heaters tells me that the O2 is functioning fine. Once plugged back in it reads, drops the slow response codes and soon after sees a lean issue. I tested 2 difference sensors and they both acted the same way. We smoked the intake and there were no leaks. If I don't find any exhaust leaks I'll try a MAP sensor I guess.

[comanche]

Yep, check for exhaust leak first.

If nothing found, see if you can post a screenshot of your complete data screen.

We'd need to know all kinds of stuff...
O2 sensor info over time, idle
Map sensor voltage over time, idle
Coolant temp sensor voltage over time, idle
TPS

Etc

We can look for abnormalities.

Still.... it does sound like the O2 sensor is reading a false lean code.
Which the PCM would compensate for by adding fuel.
If there was a lot of false air, the PCM would add lots of fuel.

Do you have a chip? I thought the max short-term compensation for fuel trim in GM was +35%...... +49% just doesn't make sense for a stock GM vehicle.
MAF voltage over time, idle

[Th0r]

I torqued the header down, and was actually able to get a full turn on the wrench on two of the bolts at the drivers side.

No more codes! I really hate it when everything is a simple fix that I over looked, but love it when it costs me nothing to fix it haha.

[Vic28]

well good for you, hope that solved it.

[comanche]

What are your fuel trim numbers looking like now?

[Th0r]

I don't remember, but the tech that was helping me out said everything checked out when I brought it back in. I haven't borrowed a scanner to see for myself.

[comanche]

Cool. Sounds good.