E38, FI, boost, cylinders cutting out. Help!

[arubenstein]

Hi,

I am tuning an E38. The base vehicle is a 2009 Tahoe with a 5.3 and 4L60 (it is a PPV). We took the 5.3 out and put a 6.0 L96 in. The 6.0 has a supercharger on it with the smallest pulley possible (should make about 9 psi). I have had the car on the dyno for a while doing VVE which all went well. I recently shifted into doing the MAF and started to run into a problem.

My method of getting proper MAF scale is to hold the vehicle at a particular MPH on the dyno, then gently roll in to and out of the throttle, recording commanded AFR, WO-AFR and using the corrective numbers to rescale the MAF. The issue I am having is as I roll into the throttle, as I pass about 139 kpa, SEMRET starts to roll in and increases as I get further into the throttle. I see this is anoted as "Torque Reduction Retard", but I have no idea where this is coming from. The T43 has a calibration on it to never upshift or downshift from 3rd, so it certainly isn't from that. I have also (at least I think I have) turned off all formes of torque reduction. Eventually, as I pass about 148 kpa, SEMRET drops to zero, and the WO starts recording a very lean condition (goes from 9.7 to off-scale high). I attribute this to fuel being cut in some cylinders, which is evidenced by a feeling and hearing a very symmetrical cylinder loss.

Note 1: Yes, I know the AFR is way, way low - that is why I am scaling the MAF to correct this. But I don't think this is causing the issue.

Note 2: When I say "symmetrical" it is a very similar feeling to when traction control kicks in in other GM LS cars I have, where you hear one or two cylinders shutdown. This is not a random cylinder loss, and I believe that the shooting up of AFR is evidence of fuel injection shutdown on one more cylinders.

Note 3: I also see the burst knock, but I don't believe that is attributing to my issue.

Note 4: HO2S11 is disconnected (that is where the WB is plugged in).

So, my question is is this: What have I missed in the calibration that is causing SEMRET to kick in, especially considering there is no up or downshift happening? And, why is the ECM cutting fuel to certain cylinders? I believe these items to be related, an effort by the ECM to reduce torque. But why is it doing that? I have disabled TM everywhere I can find it.

The E38, T42 tunes, and a log of this happening are here:

17699
17700
17701

[kjlindgr]

I'm sorry I don't have much to contribute, but I've run into issues with SEMRET as well. I scoured the E38 and T43 for anything related to torque management and still couldn't find where it was pulling timing when I stabbed the throttle...but it still was. I too want to know where to resolve this if possible.

[Tre-Cool]

C0805 seems a bit low.

I think you should redo your operating zone rpm boundaries, they are pretty low.

I tend to have 5400rpm as the highest zone, scale it from your base 1000rpm.

B2523 should probably Yes

That's what I can find in the ecu tune.

[DURAtotheMAX]

I thought the 4L60 only used the T42??

[arubenstein]

Comments and updates:

- agreed on C0805. I didn't realize that was grams/sec, I looked at it quickly when I changed it thinking it was percentage. I changed that to 512 grams/sec. This made no difference to my issue.

- I intend on using a very low RPM for cross-over into "high speed airflow calcs" (B8024/B8025), so the VVE table above about 2200 rpm is not too important for me. That is why I changed the RPM zones.

- Yes, the TCM is a T42 - my mistake.

[Tre-Cool]

my bad, didn't pay attention to see u were still using the maf.

[arubenstein]

I still haven't figured this out. I am still getting GM.SEMRET even though all forms of TCS are shut off. And it is clearly not during a shift. It just seems that as I roll into the throttle, once I pass some sort of threshold GM.SEMRET builds, then all of a sudden around 3200-3500 RPM it just goes away.

Any thoughts?

17866 - log
17867 - e38
17868 - t42

[arubenstein]

I am working this hard. Some things I have found is that GM.SEMRET starts to come in as TRQENG_C approaches 500 ft-lbs. And it keeps pulling timing to keep it at 500 ft-lbs. UNTIL PE kicks in, and the GM.SEMRET drops to zero. So, to reiterate, it is pulling timing and then as soon as power enrichment is triggered, the timing is no longer pulled.

I also pulled the tune into HP Tuners, and notice a bunch more torque tables that I am going to mess with and see if they resolve the issue.

[limited cv8r]

Have you looked at this thread before?
https://forum.efilive.com/showthread.php?18710-Improving-shifts-via-the-ECM&highlight=torque+model

[arubenstein]

Have you looked at this thread before?
https://forum.efilive.com/showthread.php?18710-Improving-shifts-via-the-ECM&highlight=torque+model

I had not looked at the thread, but it is not applicable. That talks about getting the ECM to report the correct torque numbers when not using a MAF so that a 6 speed transmission / T43 will shift correctly (since it is torque based).

But:

- I am using a MAF
- The torque numbers reported by the ECM appear accurate, or at least plausible.
- I have a T42 and a 4 speed.

[joecar]

Even if you have a T42/4-speed, the ECM torque model can be used to modify shift feel.

[arubenstein]

Even if you have a T42/4-speed, the ECM torque model can be used to modify shift feel.

I am not disputing that. However, it seems like an incorrect way to do it. I would think you would want the calculated torque amount to be correct.

In any event, this is not the issue I am having and has nothing to do with the original issue.

[joecar]

You do want the calculate torque to be correct... however, if the TCM is not commanding sufficiently high line pressure, then you have to fool it.

[arubenstein]

You do want the calculate torque to be correct... however, if the TCM is not commanding sufficiently high line pressure, then you have to fool it.

I agree, but again, that is not the problem I am having.