Mean Green z28

iTrader: (19)

We've been having a hard time with this truck as it's our first E38/T42 setup we've tuned and it's been a headache with the damn VVE table. Disabled MAF and tuned VVE, and had to scale the tune down due to a weird issue of lean spikes under boost. Now we've got the VVE pretty close (although slightly rich, which we're working on) so decided to plug the MAF wire back in and test it out with MAF. Haven't really tuned the MAF table yet (its been scaled though) but it's a bit rich and the damn weird spikes are back!

Can we be hitting the 512 g/s limit on the ECM? It's scaled so it should never see that. Is there something in the T42 TCM that's causing any torque reduction now that the MAF is plugged in? Is there something in the TCM that needs to be scaled too?

Are we kidding ourselves to think we can run a MAF at these levels? Hit 14.5 psi ... runs like a raped ape in SD open loop, but with MAF enabled in open loop, it does its little dance at the top end (3.5-4K and above).

Really looking for some input from the boosted guys, I know there's a bunch here.

Three6GMC

iTrader: (11)

I went to speed density pretty quick on my boosted LSX simply because the turbulent air was causing the MAF (stock & ls7) to read erratic. Could never really dial it in so swapped to a 2012 Silverado OS that supported 3 bar and never looked back. Running the ls9 map and a high resolution IAT sensor and drives awesome. WAY smoother then with the MAF

mdwatts11

iTrader: (4)

That is the same issue I am dealing with. It is something to do with going into PE. We have it narrowed down while WOT to about a .5 a/f spike so I'm just running a rich tune right now.

I am going to buy a 2 bar MAP (12615136) and we are going to tune with that. We were thinking maybe the map can't keep up.

Mean Green z28

iTrader: (19)

Running a 3 bar map on mine. We may have figured it out but haven't really done a pull yet. We had CAT protection On. Also leaned out the MAF a bit. Was able to push to 16.5 psi (by accident while I was looking at Wideband).

madmann26

iTrader: (7)

I'm more than happy with my SD tune. Keep in mind I'm running a P59 controller.

Mean Green z28

iTrader: (19)

So we played with the IAT scalar for the injectors and figure out that we had the curve backwards. This really helped flatten the AFR as IAT increased. Then switched to a MAF only open loop tune and worked on it today and got it running pretty close at up to 12k hz in about 14psi. Now since we modified the IAT scalar, we need to go back and mess with the VVE (that's now completely messed up in the upper RPM range, doh) and hopefully a few iterations of that and we can let her loose! Have set the TruBoost to about 14psi but maybe reduce setting A to about 10.
Its weird, if I get on the throttle slow, I reach a higher pressure than when I mash is and go 100% from a dig. Maybe the final bit of playing around will settle it all up or maybe that's the nature of the beast.

SUTTERERMAN85

iTrader: (40)

Im running 12lbs on mine maf only and it is working perfectly. WOT in this warmer air im hitting about 11k Hz

adunphy

In response to the question about maxing the ECM MAF limits, its easy to check with a scanner. I use HPTuners but any will work. Just log the MAF flow in g/s. I can tell you 13psi boost is where I am maxing out the limits of the ECM on my 4.8L E38/T42 setup. My tune is scaled 50% for my injectors so I hit a max on the scanner at ~256 g/s. You can see clearly in the log where it flattens out at that value and then my AFR starts to drift a bit.

Keep in mind any scaling you do in the ECM does not lift any limits it just brings the rest of the tune relative to those limits down by the scale factor.

HPTuners does offer a custom OS that allows that MAF to get up to 15,500 Hz which may buy you a few more PSI of boost. They call it an SD OS, but you can run MAF. It also lets you dial in PE in boost areas relative to MAP which is super helpful for getting PE at part throttle

Choda

iTrader: (1)

Interesting read. My 2009 is still on MAF at 12 psi. Until my tuner says to go to SD, I'll be leaving it alone. I do wonder what mine is reading, ill check it out the next time its plugged in.

Mean Green z28

iTrader: (19)

Thanks for all the input guys. We got it very close on the VVE table and then we got it very close on the MAF table. But then we went from open-loop to closed-loop and it all fell apart. I'm wondering if I need to relocate the passenger side O2 sensor to the downpipe as the area it's in has a lot of turbulent flow with the merge and wastegate etc. And that's probably causing issues and pushing the engine to cut fueling ... we're getting the crazy lean spikes again in Closed-loop.

Seriously pissed off right now as I even went back to a open loop tune that i knew worked great for tuning the VVE or MAF and it runs completely different now under boost. I can barely make 3psi before it starts acting stupid while the same tune used to support close to 15 psi while dialing in MAF and VVE ... the weather? Bad batch of gas? It's really frustrating.