Baro changes while engine running on 3bar OS

[bradyzq]

Hi All,

I've been pulling my few remaining hairs out over this for awhile now.

The car is a turbo 5.3 with blow-through MAF and the 3 bar OS. The engine itself is stock, and idle issues and this issue (which may be related) aside, runs nicely.

I was finally able to catch the baro dropping while the engine was running in a log. I'm at sea level, so 101kpa is correct. It dropped to 90 kpa a minute or so into the log and the MAP went up by 10kpa. Fuel trim chaos ensued.

Any ideas what could cause this? I thought the baro was read at key on engine off just before starting the engine, then remembered for the drive cycle.

Thanks!

[bradyzq]

The car is currently showing the following DTCs:

P0103 Mass or Volume Air Flow A Circuit High (Pending, Current) (MAF failed for SD at the moment),
P0107 Manifold Absolute Pressure/BARO Sensor Low (Pending, Current).

[5FDP]

What MAP sensor are you running?

Those linear and offset settings are wrong for a 3 bar map. VE table is way messed up, MAF fail high is set to 1,000hz yet you are trying to run with a MAF?????? Also the dynamic airflow it set to 7,000 but you're still trying to use a MAF???

It's just all wrong if you wanted to use a MAF.


At this point you need to just ditch the MAF, this tune it just all screwed up with you trying to keep it. Speed density is far better for this setup.

[bradyzq]

I apologize. I see now that I didn't mention that I was running it in SD for now.

It is currently SD only, so I can dial in the VE tables. Yes, it is a bit blocky, but, 1200 RPM and lower aside, what's wrong with it? That lower area is impossible to dial in right now because the baro switch thing keeps happening. It obviously makes a difference up higher too, but not as much.

The MAP sensor is a genuine (not Chinese knockoff) ACDelco 12623671 3.3bar MAP sensor. The pressures equates nicely to the dyno's MAP sensor.

[5FDP]

It's not in speed density yet, missing a few settings.

MAF fail high needs to be set to zero, all 3 MAF dtc's must be set to first error to drop straight into SD.

[bradyzq]

Thank you for pointing out that I was still on second error. Fixed now.

I had read on here that setting MAF fail high to 0hz could cause issues on some PCMs, so I entered a non-0 frequency well below what would be seen at idle.

But the MAF was failed already. See my second post. So I _was_ in SD!

[bradyzq]

So, what about the baro dropping to 90kpa once the engine is running?

[5FDP]

Without the dtc's set, it wasn't properly in speed density.

Also no logging MAF pids when tuning SD, it can skew data.

[bradyzq]

More searching has led me to believe the MAP sensor itself doesn't play well with low absolute pressures and therefore voltages.