Rich decel after removing LSA blower and going twin turbo.

[Jason Austin]

This has got me stumped. Didn't have a problem with the LSA blower, but now since I've moved to twins and an LS3 intake manifold I have a rich deceleration problem. I've ran into this before and it was a simple fix. The LTFT Idle Cell Thresholds.....but, now it's something new.

I've done away with the map sensor that was on the LSA blower snout. I think that could be causing these issues.....cause, I don't know what else could be doing this. Any inputs would be helpful.

I've lowered the min pulse width, no change. I've lowered the short pulse, no change. I've messed with the VE table for those cells, no change.

Anybody remove their LSA blower and go twins that can post their tune so I can compare and see what's different with various map related tables? I figure it's probably map related, but I don't know what's reference the 3 bar sensor I'm still using, and what's referencing the old 2 bar sensor I'm no longer using since I don't have a blower anymore.

Thanks for any help/ideas.

Car is a 2014 CTS-V
Dart LS Next 427
Twin T67s
ID1300s
LS3 Intake Manifold
102MM TB
Stock Maf

[Jason Austin]

So, I just reconnected the Map sensor that was on the LSA snout to a vacuum source on the LS3 manifold. No difference.

[Lakegoat]

You still have the 3 bar map data in the tune. Do you have a map sensor installed in the intake? Sounds like you removed the map sensor? Couldn't figure that out reading the post. You have DFCO turned off in the tune.
If you have a 2 bar map sensor installed, you need to change the data in airflow.

[Jason Austin]

You still have the 3 bar map data in the tune. Do you have a map sensor installed in the intake? Sounds like you removed the map sensor? Couldn't figure that out reading the post. You have DFCO turned off in the tune.
If you have a 2 bar map sensor installed, you need to change the data in airflow.

So, LSAs have two Map sensors and one Baro sensor. The three bar is a boost reference and the other 1.5 bar (I said 2 bar and was incorrect) goes pre throttle body and doesn't see boost with the supercharger. I've not changed the 3 bar out at all, it's the same one that was being used when the car was supercharged. I've since reconnected the second MAP sensor to see if that was causing my issues.....it did not fix the rich decel.

DFCO is disabled.

[Lakegoat]

Set your DFCO to enable with the stock numbers and see if that is the problem.

[Jason Austin]

I'll give that a shot. Thanks for the ideas.

[pannetron]

I believe the stock LSA used three MAP sensors: one for actual intake manifold pressure which will indicate boost or vacuum, one just *behind* the throttle plate that indicates pressure ahead of the blower (which will read close to atmospheric at WOT down to manifold vacuum pressure on decel, no boost) and one that simply reports ambient atmospheric pressure. You definitely want the first and third MAP sensors connected and properly calibrated. Only the first one needs to be like a 3 bar sensor. I'm not sure where or if that second sensor would make sense to install on a turbo car. I think the LSA OS used it to calculate the pressure ratio across the blower.

The Airflow->Speed Density->Dynamic Airflow->Manifold Volume setting in your tune is set to 11 cm**3; that should be more like 10,000 and will have a significant effect on tip in and tip out fueling.

[Jason Austin]

I believe the stock LSA used three MAP sensors: one for actual intake manifold pressure which will indicate boost or vacuum, one just *behind* the throttle plate that indicates pressure ahead of the blower (which will read close to atmospheric at WOT down to manifold vacuum pressure on decel, no boost) and one that simply reports ambient atmospheric pressure. You definitely want the first and third MAP sensors connected and properly calibrated. Only the first one needs to be like a 3 bar sensor. I'm not sure where or if that second sensor would make sense to install on a turbo car. I think the LSA OS used it to calculate the pressure ratio across the blower.

The Airflow->Speed Density->Dynamic Airflow->Manifold Volume setting in your tune is set to 11 cm**3; that should be more like 10,000 and will have a significant effect on tip in and tip out fueling.

You are correct on the sensors. I have all three connected. Also, I caught the table you mentioned. it's been corrected with no change to the rich deceleration. Thank you for pointing that out though.

It's interesting that only STFTs peg in the negative -28 and LTFTs don't do anything. I wonder if this is just maf related. My LTFT Idle Cell Thresholds have been set to max VSS because when I was supercharged, I had a rich deceleration issue and that was the fix.

I reverted the DFCO settings back to stock, no change to rich deceleration.

I wonder if I have to lower the LTFT Idle Cell Thresholds back to stock and then adjust the maf. I suspect If I enable those thresholds, LTFTs will follow STFTs on decel. If that happens, maybe I can adjust the maf for those HZ and get ahead of the rich issue. That might now work though since I'm not rich during the same maf HZ at idle (3,200-3,500 HZ).

[Jason Austin]

So car runs amazing in speed density. I had to adjust alot of the VVE tables, but it didn't take much. No rich decel on SD. I suspect I coated the maf with oil by accidently losing the scavenge pump while idling and pushing oil in the compressor and turbine housings......or, it's in a horrible spot for low airflow metering.

Either way, i've narrowed it down to the mass airflow sensor. I'm going to clean it with electrical parts cleaner and enable the maf and see if the rich decel is still there.

[Jason Austin]

So, when I re-enable mas airflow sensor control, it's still rich on decel.

My theory is, I broke the sensor by dropping it (yeah, I dropped it) or it's too close to the 90deg bend going into the throttle body.

Either way, I ordered a new mass airflow sensor tube that has the sensor a couple inches back and I ordered a new GM mass airflow sensor. The mass airflow housing has a screen for straightening airflow, so fingers crossed this fixes my issues when enabling the mass air flow sensor.

On another note: Could me mass airflow related, when I cross 3K RPM, my timing drops to 0. This is around 105KPA, It comes right back, but it's like very noticeable, hopefully it's related.