oakley6575

iTrader: (5)

If the motor hasn't been properly tuned for higher boost levels, and your expecting your MAF to "guess" for you, then your just setting yourself up for disaster. Especially in a FI application.

A MAF can only handle so much airflow. 12psi seems awfully high for a MAF. Once it's maxed out, the computer fails it and references the VE table.

OP, do you know what the tuner changed in the tune? and what did reference while tuning, (wideband, fuel trims, ect.)?

Atomic

iTrader: (42)

Lets put a visual to it...here is a typical 2 bar ve table. If the OP is using a 2bar instead of the maf, this is what his tuner is working with to control fueling.



The actual values arent important, but do notice the axis. If the pressure exceeds 210kpa, which is ~15psi of boost, then the computer has no idea how much air is actually getting in because that is the limit of the sensor. It doesnt know if its 0.0001kpa over or 100kpa over. So it will retain the last value in the table and assume thats the pressure, so the more boost you add the leaner it will become.

Alternatively, if he is still using a maf, this is what the calibration curve looks like:



Notice the bounds: 12,000 hz. Additionally there is a 512g/s limit on the stock maf. Which ever one is reached first is the limit on the amount of air the maf can measure. In this case, if the maf limit is exceeded the pcm assumes the maf has failed and goes to use the ve table. Unfortunately with a maf tune and boost, you still use the stock MAP sensor, which cant read any amount of boost. So when that happens the mix goes very lean because the computer reads 0psi and you are at your boost level. Or the pcm may enable limp mode, im not sure.

Point is, if the limits of his tune are exceeded the computer will have no way of knowing the boost and cant fuel for it. Also, if the tuner did not account for that areas above what were actually tested, ie, if the most you see is 150kpa and he didnt interpolate the 150-210kpa values correctly, the fueling will still be wrong.

Ferocity02

iTrader: (59)

Good info, man. Thanks!

How does a MAF/SD hybrid tune work? I talked to Jim at Calspeed and he said he does a tune where it operates on the MAF out of boost, and then SD with a 2-bar MAP sensor when in boost.

Atomic

iTrader: (42)

He must be using some sort of custom OS from efilive for that. That is not a typical setup.

oakley6575

iTrader: (5)

Yes, exactly. Great explanation.

OP: is there any way you could post the tune?

HRHohio

Both Jim (CalSpeed) and the guy who tuned the truck use HP Tuners. The truck has a new 2 bar Map I believe. I think I remember hearing the tuner say that he tunes off the MAF up to the limit of the MAF and when it exceeds the limit, it defaults to the MAP (or SD tune??). Or something to that effect. I think that's similiar to what Atomic was saying. Sort of a Hybrid tune.

Also, the tuner is very experienced and is recognized as a very good tuner here. But stranger things have happened in Vegas...(we're just not allowed to talk about it).

Atomic

iTrader: (42)

That would be very interesting considering they dont even reference the same values....the maf goes by hz, and the map goes by pressure. The HPT 2bar and 3bar OS's disable the maf functionality. There is also no way to change the map sensor range settings with a factory 1bar tune. Basically, you cant use the MAF for anything but an IAT sensor if you exceed its measurement capabilities and use a 2bar (or 3bar) sensor.

HRHohio

Okay, maybe I'm not explaining it correctly, or didn't fully understand how it was explained to me at the time... that's very likely.

From Oakley6575: "A MAF can only handle so much airflow. 12psi seems awfully high for a MAF. Once it's maxed out, the computer fails it and references the VE table."
^^ This is what I was thinking was happening, or something similar.

Also, 7 psi boost shouldn't max out the MAF, or? RWHP @ 7 psi was 311. So focusing on that first (forget about the 12 psi part for now). What could be causing low hp @ that boost level??? We can worry about the 12 psi part after, although they may be related.

What do you think is going on at the 7 psi level to get so low rwhp? Keep in mind, the truck did 300 rwhp before the turbo.

Hawaiian_Built

iTrader: (15)

Finally able to jump on the computer, been really busy.
FYI, HRHohio was there for pretty much the entire install, tune and dyno so he pretty much knows everything going on with the truck.
I contacted racetronix but the refered me to This & This. I wasnt planning on spending close to $300. I ended up picking up a pump with install kit up a walbro 255 from a sponser on LS1Tech for $105 shipped.
I didnt change the spring for the 12psi nor did I have it tuned for the psi. It was street tuned at 7. I just couldnt beleive the numbers on the dyno for the first run (7psi) and pretty much said **** it if it blows. I just turned the boost up at the controller. At the time I did realise it wasnt safe, but I was pissed. But looking back, I know it was wrong.
I'll try and get the tune file when I get home from work, but wont be able to do that for a few days.
Me and HRHohio are supposed to be doing a halfway run with Jim (CalSpeed) this weekend to pick up his camaro. I might take the truck out, if I get the pump installed, and have Jim look at it.

I appreciate everyones input/help in finding the root problem.

Atomic

iTrader: (42)

That is fine, except it will be super lean unless the tuner magically guessed the correct ve values for the very specific boost. Considering the wideband said 11.5 the whole time I find this very unlikely. MAF doesnt care about boost, it only measures air mass. Air mass depends on pressure in the form of density, so depending on head flow and temperature, you can max the maf at 2 or 3 psi or even less.

My guess is the tuner took out a ton of timing to keep the engine safe. A look at the tune will say a lot...