WTF is this???? Baro plummeted mid run, momentary lean out. 6.0L L76 TVS1900

[dingo16123]

Hi all - I have a head scratcher here. What I have here is something really strange in the middle of a pull. The AFR leans out momentarily, along with some funny stuff with the baro. IDC shows the same momentary reduction associated with the lean spot. Commanded AFR doesn't show any changes associated with lean out. Fuel pressure has a spike right in the same spot as the lean out. (Yes, I know pump is falling way behind, but have been able to work around so far and walbro 450 is sitting on the bench) I believe fuel pressure spikes because IDC goes down and the pump catches up for a bit.

Now for the head scratcher..... Baro seems to jump from 100kpa down to 90kpa right at the same time all this other stuff is happening. WHY in the world did baro take a sudden nose dive? Unfortunately I only logged baro every 10s so I don't see the actual transition, but you can see it in the boost trace. The boost (calculated Math Parameter (MAP minus baro) suddenly climbs at the same time as the lean out. MAP is a 3-bar LS9 sensor and you can see that behaves perfectly, no funny jumps up or down. Actual boost is nice and steady, not that a TVS would jump boost like that anyway.

baro plummet.JPG

Any baro drift discussion I've seen is in regards to the Baro climbing when the MAF is pressurized. Any idea what is going on here? Is there a separate baro sensor in these trucks, other than using the MAP?

2007 Silverado NNBS 6.0L L76 E38, TVS 1900, Kooks headers

[GHuggins]

SC inlet offset and MAF counts - I don't ever mess with these - not sure why you changed them? Also never before heard of the baro doing any sort of update at 5000 rpms - its typically right after you floor it out and I didn't see the map changing... There isn't by some weird chance another map hooked up in the inlet somewhere before the compressor blades is there? Almost looks like part of the ecm is seeing a voltage difference screwing with some of the seen inputs because it can't be a 5v output due to the map staying the same??? Odd one indeed...

[dingo16123]

Sorry, but I'm not following on the SC inlet and MAF counts. If you're talking about the SC Inlet linear & offset on the SC/TC tab, those are set to stock. I never changed those. You lost me on the MAF counts, but I don't recall changing anything that rings a bell there either. There is no other MAP in the intake that I'm aware of. It would have to be in the MAF but there aren't enough wires (5 wire MAF housing) to support an integral MAP.

So if I can't find this mystery baro sensor, is there anything to turn off the WOT update?

[GHuggins]

I just compared your tune to another one - showed those had been changed - perhaps an odd OS where the OE changed them, but I've never seen them set like that before? Is it possible your vehicle had been tweaked before?

Only way to kill baro updating is to do an enhanced OS install - 2bar upgrade and then put in your map settings...

[dingo16123]

Those numbers haven't been changed since I've owned the truck and it was pretty much bone stock drive train when I bought it.

Ok, I was planning to look into the 2bar anyway, so I'll do that now. What are the primary benefits of the 2bar besides Boost Enrichment and higher MAF limits? Everything else appears to be similar. In fact, is there even any benefit on the VE table side because the stock OS VE table goes to 2bar as well. Are there any downsides to the 2bar OS on the E38?

I'm not seeing any Baro update settings on the 2bar OS. Are there settings or does it kill the baro update by default? Does the 2bar OS lock in baro at startup and keep that until the next startup?

Thanks again for the help!

[GHuggins]

The only good thing about the enhanced 2 bar OS in my opinion is the baro update kill - it does this by default in the core programming - only updates on ignition cycle... I don't see any point in boost enrichment because if your VE and MAF tables are dialed in correctly they do the exact same thing and the ECU is going to use the richest of the PE settings anyways...

The OE VVE table actually gives you more cells for tuning and dialing things in better - you can change the values in the enhanced OS table, but not add any additional rows...

[dingo16123]

Good point, I did see the loss in resolution of the tables.

How exactly do you control enrichment at say 2000rpm at various levels of boost? Assuming you go into PE before 100kpa, you'd be commanding same fuel at 0psi boost or 10psi. Same goes for 6000rpm. I was trying to get away from going from stoich right to full enrichment at or below the 0psi boost range. I could see how you could bake this into the VE, but not really the MAF. It wouldn't be a 'proper' VE then anyway. I suppose with a centrifugal, and maybe some turbos, you could make this work without boost enrichment because boost is RPM related. For a PD blower, I'm foggy how you would do this without boost enrichment.

[GHuggins]

I set them up via pedal settings to go into PE at around 2 to 3 psi...

I still think you have something else going on with voltages to cause the problem your having - if the 2 bar OS doesn't fix your problem - I would check into this and then if you have it - disable desoot mode...

[dingo16123]

Ahh good thinking! I assume you are talking about PE THROTTLE/PEDAL? I could log throttle vs boost and get a pretty good idea where I'm going into boost at different rpms. At peak torque I suppose you could go into PE a little sooner than 3psi if needed. Now, are you able to taper in from leaner PE (12.5ish) into full boost PE (11.5ish)?

I'll run it a while longer like this and see if it happens again. So far, it's only happened the once that I've seen. I'll up the voltage sampling rate and see if I spot anything. I didn't see anything in the other sensors that might indicate a system wide voltage problem. No DESOOT here. Is that something that needs to be special requested for my OS?

[GHuggins]

Desoot is only available for some of the E38's and E67's... I use the rpm settings to taper in commanded air fuel / 15 to 1800 and below target 12.5ish then full air fuel or lambda ratio above that and that depends on boost capabilities below that rpm level...

You'll have to log PE tps to adjust the tp settings...