New 02 sensors and MAF 6 months ago. I developed some exhaust leaks in January pre-o2 sensor, nothing serious but started to get lean codes. Had a hell of a time fixing those but they are finally done, however I am still getting lean codes P0171 P0174 P1174 P1171 and a very rich mixture as a result. Black watery soot coming out the tail pipe.

Already did the entire tuneup plugs, wires, packs, all that about a year ago. I have been fighting this for way longer then it should have taken me and before I go throwing money at new parts I would like to have a general consensus on what to do. My 02 voltages are moving but minimally, currently at .2 volts and .08 volts moving plus or minus .2 and .02% respectively. The only real change is coasting when they go to 0v. My MAF is also reading ~6.5 g/s at idle and jumps when I hit the pedal.

So my MAF is showing what everyone else seems to get at idle, so it doesn't sound like an intake leak, but I did look around and saw nothing. My o2 sensors are moving, and are only 6 months old, so I am ruling that out as well. I just fixed exhaust leaks, also ruled out. What am I missing? Can it still be an intake leak? How of a leak would I be looking for? I looked around, pulled a few vacuum hoses and they all seemed to be tight and started hissing after being pulled, no hiss prior. I also reset my adaptations, now I've got no idea what to do except replace oxygen sensors and the MAF again..

 

A smoke test is often recommended to find an intake vacuum leak. If you're lucky it'll be one of the vacuum lines or vacuum line fittings, but there have been reports of leaking fuel injector O-rings causing vacuum leak lean codes.

 

Your symptoms suggest unmetered air entering the system after the MAF. One way they can do that is from vacuum leaks. I can confirm that failing injector O rings do cause vacuum leaks and lean running codes. Also I can confirm that the upper intake manifold bolts not being tight can also cause such a leak, as well as the SAI system.

 

You are getting lean codes, but the truck is running rich. Sounds like an oxygen sensor issue. The oxygen sensors override the MAF when they are functioning correclty. Chart the oxygen sensors on cold start, they should go to close to 1v initially, then slowly come down. You can unplug the MAF and see if it makes a difference.

 

what brand O2 sensors do you have? I had a few bad cheapy ebay /amazon ones fail me. Went with walkers. No more issues......

 

-I'll figure out how to make a smoke tester and test for vacuum leaks... Is there any special instructions for this truck or just hook it on one of the lines? Will I be able to see it coming out of the fuel injectors with the upper intake still on?
-I'll also try tightening down the upper intake first and see if that helps, hopefully it's something simple but is it ever ?
-The MAF was reading around 6.5g/s which after checking around the forum seems to be the normal. That's why I wanted to rule out a vacuum leak but I guess better check then throw parts at it.
-My 02 sensors all start at .45, then maybe jump up for less then a minute and then drop and settle very low. Minimal oscillation. I just did a 45 minute drive with it because I had for the majority of the ride B1S1 .25 B2S1 .05
​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ ​​​​​​​ B1S2 .05. B2S2 .25

-Also I have all 4 Bosch sensors and they were replaced at the same time

They seemed to be swapped in their readings which is strange (they are in the right positions)(i checked) but again minimal oscillation and movement unless decelerating and they go to 0 volts which is normal. Because they are going to 0 volts I am assuming they are reading correctly.

First step i guess will be the smoke test and I will be back with more info when I get it.

 

I bought something like this where you add mineral oil and hook it up to an air compressor.

 

Someone on here recently had 02's that were behaving like yours and it wound up being the 02's. I was surprised because they started out near 1v and then trended down as the engine got hot. You might be able to force the 02's to climb by richening the mixture at idle. Disconnect and remove the MAF from the air inlet and open an unlit propane torch wide open in to the air inlet. The propane shoudl richen the mixture, depending on how lean your engine is runnning it might cause the 02's to climb up above 0v. You might want to try just disconnecting the MAF first, without the propane, just to see if that makes a difference. DOes your OBD Reader have chart function or only digital readout?

 

Just got done making my smoke tester using an old pickle jar, soldering iron, and some hose I had lying around...

Iron on

Full setup minus the air hose to provide pressure(1-2psi)

Seal these off

Lots of smoke

No vacuum leaks that I can see, maybe the smallest bit around my brake booster attached to the manifold but nothing to cause such lean conditions on the oxygen sensors

I’ll try and disconnect the maf and see how the readings change and then add the propane if I still get nothing as suggested by Extinct.

I do have a chart function and I’ll upload that as soon as I get it charted out

 

Went to chart out my current voltages before I disconnected the MAF and added propane but the damn thing just magically started working?

Pain in the *** these trucks.

Maybe I just have some left over mineral spirits from the smoke test sitting around making it smooth out but I highly doubt it after a 15 minute drive.

All I did for the smoke test is disconnect and reconnect some vacuum lines and reconnect the air box. Maybe there was something loose ¯\_(ツ)_/¯

Thanks everyone for your help, hopefully she stays smooth