I have an issue with tuning one customer car, a mild 382 Corvette C5.

All fine, engine purrs like a kitten and runs well in CLSD mode whilst tuning VE tables and all of a sudden in starts to sputter between 1200 and 2500 rpm, basically lean sputter and misfire. If I richen it up sputter goes away but when looking at histograms it tries the lean out thing again. If I lean it out, next log it wants to richen it up again by same amount - whoa I thought.......
I let it run at idle and look at the wide band and i see that AFR suddenly runs off from 14.6 up to 17.0! If I blib the throttle hard enough it comes down to 14.5 stays a minute there and starts to slowly creep up again. What I see is hat B2S1 O2 sensor runs off! 900mV going down to 150mV, and hovering there.......revving oit to 3000 and it jumps back to 900mV and AFR becomes 14.6 again........above 3000 rpm it all seems fine and stable though

It is not the tune, I tried four different tunes and it does it all the time, but does not throw a code.

So I changed that O2 sensor and guess what, now the other does it as well!!!!!!!!

what the heck can couse a O2 sensor to run off, even changing it to a known good did not make a big difference.

 

Disable DFCO and give it a try.

 

I know you said it's not the tune, but thought I'd toss that out. Possibly the lean condition being experienced is being commanded by DFCO. You'll know if it is that way and then can go to work to get it right.

 

quote:So I changed that O2 sensor and guess what, now the other does it as well!!!!!!!!

what the heck can couse a O2 sensor to run off, even changing it to a known good did not make a big difference.

because the o2 is telling the truth. remember that a lying input skews the outputs garbage in garbage out. unplug the maf

 

He's in CLSD.........

 

quote:All fine, engine purrs like a kitten and runs well in CLSD mode

i guess this statement threw me off. sounds like we do not have clear info.
but with his description something is lying to him.

 

I'm confused why something is lying. The 02's are reporting lean and the wideband is confirming it. As I understand it, the engine is continually going lean at idle. The problem seems that he's chasing it and not closing in. Or am I misunderstanding the OP's situation? You could also try running it open loop to make sure it is only a closed loop problem.

 

well you may be on to something about the lying it's just bank 2 but then why does
clsd fix it?
i have seen things happen that just can not work that way but they did.
if the car has a lean condition on the right bank where was the the p0174 code? regardless if its mechanical or electrical the pcm sees lean.

quote: You could also try running it open loop to make sure it is only a closed loop problem.

i agree


an idle lean condition on one bank is sometimes a leaking intake most prominent cold but would not explain running well in clsd.

i dabble a bit in tuning and have found people will bring you a broken car.

 

well, DFCO ist disabled, as well as MAF since I am in CLSD. Just running on VE table and narrow bands along with a wide band to verify.

maybe I need to be more specific about the running off, when O2 are showing around 850mV at idle engine purrs and it is at 14.6, just suddenly it starts to slowly run off and mV go down to 150 and stay there. It does it when driving around below 3000rpm as well, above 3000rpm all is fine and O2's jump back to normal values

Whenever down at 150mV and extremely lean, a hard rev or blib most of the times brings it back to normal values until it starts to wander off again.

 

Are you POSITIVE it's actually in CL?? Truly sounds like it's in OL when this occurs.

Does your post say that DFCO is NOT disabled?? If it's not, disable it temporarily to make sure it's not causing your problems.

If it IS disabled, I recommend you force it into OL and run it monitoring with the wb. Log your MAP while testing this. Curious if it's reporting correctly.

The only things you'll be using at this moment are the RPM's and MAP. If you force it into Open Loop and it still goes lean, then either your MAP is not reporting correctly (due to failure of some sort or Vacuum leak) or those cells are not correct.
That's how I'd go about troubleshooting this anyway.

 

to confirm, DFCO IS switched off.

If I force it into OL via VCM control it does the same thing. I wonder how you could have an intake leak when your are in CLSD, it just looks at MAP and rpm and O2's. I would understand a leak when running a MAF though

I'll try a leak down test when hot and log it in OL and see what it does from a cold engine up to operating temps. Need to warm it up for the leak down test anyway

 

Whether it's in CLSD or not, a vacuum leak could cause the map to report off. This of course SHOULD still not have the O2's run off like they are. When it's in Open Loop and the O2's start running, what's happening? What's the Map doing? This sooooo much sounds like it's in OL.

 

I did some more through checks now playing around with forcing it into OL and CL and actually it is the controversy. When in true OL the O2 report a steady signal, MAP around a steady 45 kPa. I logged it from a cold engine to about 100 degrees C, about 210 F. A steady 850mV on both sensors. Only if I enable OL STFT O2 start to wander off, if OL STFT is off signal is rock steady.

I just re-enabled CL (changed closed loop enable temps bak to stock) and O2'S run off but MAP stays at 45kPa. This is clearly a CL issue and I am not aware what can cause it.

puzzles me

further checks now:
-leakdown test bank2 no significant differences, actually on LG headers this is driver side because sensors are crossed out at least this is what I see on car.
-swapped spark plugs, wires and coils left to right - no change
-if I disconnect B2S1 sensor it stays at a steady 450mV
-removed intake manifold to check anything loose, all OK, no leaks

as soon as I reconnect that O2 it stays for 30 seconds at AFR 14.5 and starts to wander off. Hard to believe that the known good sensor we swapped in shows the same fault!

as soon as hitting PE table all seems fine

 

so I believe I found it, or better found it all............

christ sake, so many small issues can drive one nuts.

actually the minute I wrote about the crossed O2 sensor wires a light bulb went on, how can the PCM compensate for if it measures bank2 but controls at same time bank1?

that's why it drove so badly when it came in, plus, I heard a small hissing sound and took intake off again, about 3" into the wiring harness the plastic tube was kinked and broken, it was connected at the intake but it created a small air leak every now and then. Couple that with a defective spark plug wire all on same side you get a lot of fun.

so far, idles at a rock steady AFR of 14.4-14.7 and mV jump up and down as they should and did no longer run off. A test drive tomorrow will show if I was right for sure.

 

Chasing multiple problems sux. Congrats.