C450

How sensitive are o2 sensors? I'm working on a 5.3 with MP turbo. My long term fuel trim on bank 2 reads good. Bank 1 is reading 25. I found an exhaust leak and fixed it but it hasn't changed the ltft readings. Just bank 1 is running super rich. Plugs are fouling out and I keep changing them to make sure I don't have a dead cylinder causing my problem. I've changed out new intake gaskets with another set of new gaskets. I'm convinced I do not have a vacuum leak. Could a pin hole in the exhaust be causing a false reading at my bank 1 o2 sensor? I'm not seeing any holes but I'm about to pull my crossover pipe off again and check it out. Would anything else cause this issue?

58Rag

Either a faulty O2, or you really do have some sort of unmetered air causing the issue. A pin hole will not cause +25 LTFT. You may need to try to manipulate the O2 by enriching it ( I prefer propane ) and see if it begins to bring down the readings. Basically, you need to figure out whether the O2 is stuck lean or not. Then go from there.

C450

Hey thanks for the help. I'll try the propane but what is the best way to do that? Inject propane through the throttle body or drill and tap a hole to inject propane upstream of the o2 sensor?

C450

I should also add that these are new , but cheap, Bosch o2 sensors. If I need to replace one, what o2 sensor would you recommend for a 2000 silverado?

58Rag

Seeing as you are referencing to LTFT, I'm assuming you have a scanner. With that said, just pull a vacuum line on the manifold and attach a hose from the propane bottom to the manifold. I have a metering tool I got from Kent Moore. Get your data pulled up ( both front O2's) and slowly meter in some propane. As you do so, both O2's should go to 850+mv no problem. If that one is still stuck at like 100mv...I would make sure the wiring, power and ground are good to it. If all is good there...replace it with another factory O2. Hope this helps.

C450

I appreciate your help. I'll give this a try and get back to post results. Thanks again.

JetMech442

iTrader: (1)

I had several pin hole leaks due ot poor welding skillz around my O2 bungs that were causing my tune to go way rich at idle. After adding massive amounts of weld around the joint, it was finally sealed and my ST/LTFT went back to reasonable levels and my eyes stopped burning at idle from the overly rich conditions.

58Rag

I can definitely see multiple pin holes causing that as it would replicate one big hole. But not one small pin hole. I would say if it's noticeable enough for you to feel exhaust on your fingertips, it's bad enough to start causing false readings.

2xLS1

iTrader: (25)

What makes you think Bosch O2 sensors are cheap?

http://www.bosch.us/content/language1/html/734_6641.htm

RonSSNova

iTrader: (3)

Are the sensors each placed right after the manifold?
Why not swap left for right and see if the problem follows the bad sensor.
New parts have been known to fail.
Check the wires as well to make sure they didn't get burned somehow.

Ron

C450

I said cheap because there were a couple of different Bosch o2 sensors available through Summit, as well as a few NTK. The more expensive sensors were upwards of 60 dollars. I paid 30 dollars a piece for mine. I know Bosch is a good brand, but I could have bought the better set.

C450

Ok so I haven't had much time to mess with the truck but I did crawl underneath to check for leaks. I was able to see one pin hole around a weld. I actually smeared high temp rtv around it because I didn't have a welder near by. I let it dry, ran the truck and ltft on bank 1 lowered to 11. So already it is doing better. I then crawled under again to check to see if the rtv had blown off of the pin hole. I found out there was a good size leak around the gasket of my 02 sensor. I was able to tighten it another 1/8 turn. I also put high temp rtv around the gasket before tightening it down to just make sure I get it sealed off. Let it dry, started the truck after work last night and it dropped bank 1 ltft to 4.7.

Here's a fun fact about this engine. I'm using a KB racing turbo manifold. The exhaust from bank 1 runs into bank 2. There is no separation between o2 sensors. The bank 2 o2 has to read the exhaust from bank 1 also. While I was fixing the bank 1 leak, I noticed ltft on bank 2 has now went down to -9. I know I may still be having problems with the spark plugs because I have not cleaned or replaced them and they are sooted up pretty bad on bank 1. So hopefully tomorrow morning I will throw in a new set of plugs and see if it straightens up. It definitely runs a lot better for sure. I only have a 2 lb spring in my wastegate and I'm really wanting to get it running correctly before I step up to my 60lb/hr injectors.

I didn't get around to doing the propane test but after I sealed off the leaks, the mv are fluctuating like they should on the o2's.

C450

Thanks for the suggestions Ron . To answer your question, yes the drivers side o2 is placed right after the manifold and my kb racing turbo manifold has the o2 placed just before the turbo. I believe they are located correctly. Had I not found the leaks I would have swapped o2's. That was going to be my next try. Wires look really good so far.

C450

Update : Threw a new set of plugs in after fixing the exhaust leaks and now my ltft bank 1 is 2.3
bank 2 is -1.

Runs better but now it's time for the 60 lb/hr injectors.

I hate to ask but would anyone have a 2001 5.3 turbo efi live tune they would like to share just so I can take notes and get me started in the right direction?

I appreciate everyone's help.