What causes this? STFT Question
What causes this? STFT Question There are two different things going on here. First off, I see that my STFT's are not close together from Bank one to Bank two when placed into Closed Loop. Bank 1 is reading -2% and bank two as high as _15%. Now I see this right now at idle. I am tuning in SDOL right now and I turned on the Closed Loop only to check my WB's. So I did not drive it to see if this situation happens while cruising. Also, I am tuning my 408, and this use to also happen with my 347 MS3 engine. I never did try and solve it with the old engine because I was finishing up the new 408 build. Now I have a completely different engine, new injectors, different fuel system, new sensors, different heads, different exhaust, different everything. I am still using the same coils, same factory wiring harness, and same PCM. As best I can remember the banks would come close together once I get cruising.
So what will cause this? The engine is new with about 350 miles on it. Compression is equal with all cylinders. I checked cylinder balance and find nothing. It is not vibrating like it has a dead cylinder. It has new plugs, new NB's, and MSD wires on it.
Now to the second question, the reason I checked my WB's against the NB's is because I have two NGK WB sensors on the car, one on Bank 1 and one on Bank 2. I always have. While tuning my idle my WB on Bank 2 went lean and stayed pretty steady with no changes at 14.3. The WB on Bank 1 was cycling at 12.3-12.8. Now this is before I went to closed loop. So I switched it to closed loop and the WB on bank one moved up to 14.5ish while the WB on bank 2 stayed at 14.3. That is when I noted the STFT's were off from each other.
So do you think the WB on bank 2 is bad, or do you think there is something wrong on bank 2 to make it lean? My WB are in the factory piping were the rear O2 sensors go. I did remove the cats and installed a pup in their place. My NB's are installed in the stock locations before the cat's (pup). So if I had an air leak from removing the cats I would think you would see it in the WB's but not the NB's.
Thanks for the help.
So what will cause this? The engine is new with about 350 miles on it. Compression is equal with all cylinders. I checked cylinder balance and find nothing. It is not vibrating like it has a dead cylinder. It has new plugs, new NB's, and MSD wires on it.
Now to the second question, the reason I checked my WB's against the NB's is because I have two NGK WB sensors on the car, one on Bank 1 and one on Bank 2. I always have. While tuning my idle my WB on Bank 2 went lean and stayed pretty steady with no changes at 14.3. The WB on Bank 1 was cycling at 12.3-12.8. Now this is before I went to closed loop. So I switched it to closed loop and the WB on bank one moved up to 14.5ish while the WB on bank 2 stayed at 14.3. That is when I noted the STFT's were off from each other.
So do you think the WB on bank 2 is bad, or do you think there is something wrong on bank 2 to make it lean? My WB are in the factory piping were the rear O2 sensors go. I did remove the cats and installed a pup in their place. My NB's are installed in the stock locations before the cat's (pup). So if I had an air leak from removing the cats I would think you would see it in the WB's but not the NB's.
Thanks for the help.
An upline leak in the exhaust can do this, a cylinder that is misfiring it can do this (though it shouldn't move back into line at cruise, that makes me favor leak), an inconsistent injector (unlikely for you since it existed with previous set on previous side) and even poor sealing from intake to head around a particular cylinder...
Tonight I started scanning again to see if it still did it with the WB. It does. I posted the scan. It is a short scan. Please watch the STFT and Commanded AFR to see when I switched from OL to CL and back. I do not think the STFT's moved all that much this time though. With the other engine it also had the Hooker LT headers on it and now it has the factory exhaust manifolds on it. I did not notice this when I first started this new engine up, but I also did not look for it. It became noticeable this past weekend. I did do a short burst to check to see if the turbo would build boost. I am thinking of checking the exhaust gasket between the manifold and piping to see if it blew out. I do not hear any leaking exahust though. I do have the fuel settings rich, i could have fouled a plug. There are two scans and two configs. the first scan and first config is with both WB's, the second scan and second config is with just the bank 1 WB. The second scan has some driving around and I was correcting the VE table from time to time. See what you think so far.
Well, it will not let me post the configs, if someone wants to see the config pm me the email and I will send it to you.
Well, it will not let me post the configs, if someone wants to see the config pm me the email and I will send it to you.
Last edited by Texas_WS6; Mar 21, 2010 at 10:42 AM.
