Why is my tune commanding rich?

[awest623]

I was doing some lean cruise tuning today and noticed that the tune is commanding rich (eq~.948) when throttle is approaching or at 0 and decelerating. I've looked through my tune file and can't find any reason why that would be happening. I'm hoping someone with more experience can point out where the error is.

You can see the issue at timestamps: 01:24:516-01:32:692, 02:25:483-02:30:254, 03:06:181-03:19:006, etc.

Specs:
1998 K1500
L31 (5.7) engine
P59 Swapped on a 2 BAR OS
Whipple Supercharger
43lb Injectors
Cam, Heads, Headers
Bunch of other stuff that doesn't relate

Tune and Log attached below, thanks in advance!

12JUL2023 600rpm idle-lean cruise.hpt
23-07-12 17-50-42.hpl

[awest623]

Here's my scanner layout as well, in case anyone wants to use it

12jul2023.Layout.xml

[Alvin]

The later Gen 3 trucks would do this if the rear o2's were completely deleted. There is a cat test that can be disabled but not with the current software.

[blindsquirrel]

Cat test (or Post O2 test, whichever one it's doing) on Gen 3 can't be disabled with any version!

[awest623]

Interesting. I'll have to look into that more but it makes sense. I just recently did the P59 swap and I'm using a 2005 Mexican truck operating system. I was hoping to eventually get the truck back to some semblance of closed loop with lean cruise.

[Alvin]

Honestly most people don't even know those test are being performed and its not a huge deal. You could likely get by fine ignoring it.

[TheMechanic]

Cat test (or Post O2 test, whichever one it's doing) on Gen 3 can't be disabled with any version!

You had suggested before about reinstalling the post O2's and zip tying them up. Do you do a "no reporting" for codes? Or like failing the MAF, first error with no MIL so they fail and end the continuous testing?

[awest623]

Honestly, it's just annoying more than anything. Once I re-enable DFCO it won't make a difference anyways. At this point the only reason I'm not going back to the 0411 PCM is because I don't have an operating system that supports Clutch Transition DFCO. I originally put the P59 in because the operating system supports flex fuel, just to find out that it disables flex fuel when unless you run a 24x crank reluctor.

[awest623]

You had suggested before about reinstalling the post O2's and zip tying them up. Do you do a "no reporting" for codes? Or like failing the MAF, first error with no MIL so they fail and end the continuous testing?

I might try enabling the codes. I don't believe the post cat O2 wiring is even in the harness anymore.

[blindsquirrel]

No, don't re-enable any of the codes. The tests it's running are separate from anything in the DTC list - since it's never been available in any of these PCMs I don't know exactly which one(s) it does. But like the Gen 4s, cat test/post O2 test are their own thing separate from anything else.

[awest623]

No, don't re-enable any of the codes. The tests it's running are separate from anything in the DTC list - since it's never been available in any of these PCMs I don't know exactly which one(s) it does. But like the Gen 4s, cat test/post O2 test are their own thing separate from anything else.

Gotcha. Thanks for the information

[Alvin]

No, don't re-enable any of the codes. The tests it's running are separate from anything in the DTC list - since it's never been available in any of these PCMs I don't know exactly which one(s) it does. But like the Gen 4s, cat test/post O2 test are their own thing separate from anything else.

I've heard some people would turn the diagnostics back on but turn the lights of for rear o2's on 04 GTO's (gen3) and it would stop doing this.

[awest623]

I've heard some people would turn the diagnostics back on but turn the lights of for rear o2's on 04 GTO's (gen3) and it would stop doing this.

Yup, I tried this before he made his replay saying not to. It didn't make a difference. Probably the only way I see around it is to adjust the OLFA ever so slightly lean so it doesn't command stoich and allow the diagnostic test to run. Haven't tried it yet

[blindsquirrel]

It will keep commanding rich and then commanding lean to try to get a pass/fail, forever (well, multiple times per drive cycle), in an endless loop. Unless you plug some rear O2s back in. They do not even need to be in the exhaust system, just tied up somewhere out of the way. Then, it will get a result (fail, but that's OK, since the only thing that will do is keep it from trying again).

I'm not positive, but I believe you can disable/de-pin the heater circuits on the tied-up rear O2s so they don't try to melt everything. These tests it needs to run aren't related to the heaters, I don't think they need to be there.

[awest623]

My truck never came with heated rear o2 sensors anyways. I'll give that a shot sometime. I haven't noticed it commanding lean outside of when I'm in lean cruise.