HydroDesign

As you can see, I'm new here.
My question is has anyone used the Diablo Predator to retune the computer after installing the 85 mm MAF. And if so, what did you do?

Thanks guys.

jimmyblue

iTrader: (11)

Not a damn thing, with an '02 SLP 85mm on an '02
car. Other than crank the spark to +10% and PE to +2%.

On the other hand you can find people who used
other 85mm MAFs (even folks with earlier years
who use the early-years SLP MAF) who have to get
help (custom tune) from their Predator vendor.
Some of whom do and some of whom don't give this
form of customer support (caveat emptor).

Out of the box, the Predator does not offer the
type of mixture adjustment needed to compensate
for the type of airflow measurement error that
ported MAFs, MAF ends, or some aftermarket big
MAFs induce - you only get power enrichment
control, when what you need to correct the MAF
error is a linear scale factor. Maybe someday.

HydroDesign

Thanks for the info JimmyBlue.
And I do have the MAF that has "supposedly" been calibrated for my car by SLP, but I don't see how because that was the only thing I changed between dyno runs, and I did wait long enough to let the long term and short terms adjust to whatever they adjusted to, and I saw NO power increase, or torque for that matter.
So are you saying that the only way to get what I need if I get the Predator is to buy another tuning program, through Diablo, for the MAF?

jimmyblue

iTrader: (11)

Well, that's the thing about the bigger MAFs. If it's
calibrated to stock frequency/flow (which is what any
out-of-the-box tuning would presuppose) then the only
performance gain would be from airflow, and a stock
motor does not really challenge the airflow capability
of the stock MAF.

If a MAF claims to produce a performance gain on an
otherwise-stock LS-1, then you can bet it's dicking
the airflow reporting around. Great, if your car /
year was tuned wrong from the factory. Not great, if
your factory tune was pretty much right.

If you installed a MAF and it didn't change your LTFTs
or make you knock, then I say congratulations, you
picked the right one.

It's my impression that the '98-'99 F-bodies were a
bit rich at WOT, and folklore has it that these ran
better if you leaned them out a bit. This is where
things like porting your MAF, MAF ends, and MAFs that
give you an artificially-low airflow reading come
from, I believe.

But GM changed the tune in '00, and again for the
'01-'02 years. The '01-'02 I believe are leaner tuned.
Fool these PCMs, and all you get for your trouble is
knock retard (at best). On the plus side, you got 10-
20 (?) more HP, stock for stock. Which is the same or
better than the '98-'99 folks pick up from a "bent"
MAF.

Now, you can take your non-miscalibrated setup and
tune PE for ideal WOT O2 voltage (like maybe 900-
920mV), and then dial your spark forward as far as
still avoids any KR, and figure you have pretty much
maximized the power output for the intake / cam /
exhaust limited airflow of the engine (airflow is
the prime determinant of maximum power output,
tuning is how close you come to that ideal).

Other mixture-affecting mods (like headers) may
push you outside the Predator's (current) range of
correction, then you would have to get some custom
help or go to a more broadly capable, more expensive
set of software & hardware. I'd say right about the
time you start considering a cam swap, you ought to
buy the fancy tuning & logging tools. Until then,
one-size-fits-all (especially with a friendly
tailor like RWTD) probably fits. Unless you went
and got some bad-idea boob job

Team ZR-1

You have to be aware that if you put a 85 mm MAF into a car that was desgned for a 75 mm MAF, so called calibrated or not, the PCM MAF table for a 75 mm starts at 1,500 Hz, but if you look at like a Z06 that uses a 85 mm you will see the MAF table starts at 750 Hz.

Thus every time that 85 mm ouputs less then 1500 Hz, your PCM has to barf because it cannot convert that signal and lookup in MAF table. That has worse effect on a C5 that uses drive by wire, for the ETC is well protected and a unknown freq by a MAF can ( and done to my engine) trip into reduced engine mode and that is no fun on the highway

There is ZERO reason to change from stock MAF or T.B unless your engine outputs over 550 HP.

I tested several differnet modiied MAFs, over 2 months of testing and it is all a waste of time, money and performance.
Best path is to have PCM properly tuned and leave stock MAF/TB in.

HydroDesign

Thanks much for the informative answer. I really do appreciate it.

HydroDesign

But like you said, John, the Z06 comes with an 85mm MAF, so then its just a matter of proper computer tuning for my vehicle to compensate for the 85 mm MAF, correct. And you don't think I will see any meaningful gains? Because I am pretty much stock. Any suggestions on who can give me what I need around St. Louis?

Thanks for your input.

jimmyblue

iTrader: (11)

Is this true for the 85mm truck MAF that's said
to be the basis for SLP's "calibrated" LS-1 MAFs
(the "calibration" being a resistor soldered across
two of the "struts" and an SLP badge) too? Or is
this 750Hz lower limit Z06-specific?

Dunno what the idle frequency of my SLP MAF is
or how that compares to idle frequency of the
stocker.

geniusjester

I understand your point on the MAF, but what ill effects does a ported TB have??

Team ZR-1

But the Z06 has a different MAF table in that it was designed for the 85 mm MAF and thus its table starts at 750 Hz,

If your PCM was designed for a 75 mm then I suggest you look at the MAF table and see if it also begins at 750 Hz or does it start at 1,500 Hz and if so you cannot tune for freq below 1500 for you cannot change the table's size.

The table jumps 50 Hz a step so from 750 to 1500 is quite a difference.

There is zero reason for a fairly stock powertrain to need any more airflow, use a PCM scanner, does your MAF output close to its 12,000 Hz when engine is at 100% load, nope, so why spend your hard earned money on air when most likely engine is too lean with stock MAF and you really need to look at injector sizing.

Keep in mind a Z06 also has a larger intake manifold and cam grind and I can tell you most Z06s I have tuned are quite lean under high engine load, thus again the 85 mm is lots of air when the injectors cannot keep up with that flow.
85 mm MAF comes from GM trucks for more torque but it also has air intake that is designed for that purpose and has better low end response since PCM was designed for MAF output less then 1500 Hz.

Team ZR-1

I tested a SLP MAF,
it is nothing more then a 01 Z06 MAF with
a resistor soldered across the bridge which is nothing more then a hardset MAF-T in that the output would always report XX amount less freq ( depending on resistor value) then it really is thus causing unmetered airflow.

That would not change the fact if the MAF outputs less then 1500 Hz and the PCM used MAF table starts at 1500 Hz that the PCM would be confused for it cannot compare a value that does not exist in the MAF table. Maf freq had to be converted as A/D and compared to MAF table.

Before going with a 85 mm MAF I would suggest the PCM 1st be checked to see if table starts at 750 Hz or 1500, if 1500 I would not use a 85 mm for any reason.

Why because every time I lifted off of gas pedel to decel, LTFTs would scream up to +25 plus lean while STFTs were still around zero and that was even when I changed the VE table to mirror image what a Z06 uses.

Step on TPS and LTFTs would jump right back to zero while STFTs never even went to 5%.

Randomly PCM would puke and ETC would DTC and put engine into reduced engine mode ( 99 C5 used in tests that is around 500 FWHP)

Install 75 unscreened MAF back in, tuned for 75 and all fuel trim, DTC and ETC issues went away.

Install 85 mm back again, tune for 85 and problems returned, did this
4 test cycle times, each time same results.

HydroDesign

Thanks alot for all that excellent info on all you have done, its a wealth of information. I am just gonna take the screen off my 75mm MAF, and maybe richen a little for WOT.

jimmyblue

iTrader: (11)

Well, this all got me curious enough to go hook
a 'scope up to my MAF output and here's what I
found - my SLP MAF pulse period is 374uS,
equating to a frequency of 2700Hz at idle. So
whether my MAF table starts at 1500 or 750 would
appear to be irrelevant in this case as I'm well
into the table either way.

I don't think I'm gonna have time to put the
stock MAF back just now, since lunchtime's nearly
over. But maybe somebody with a stock MAF and
auto on an '01-'02 F-body has a baseline normal
idle frequency to share. If not, I guess I'll get
to it some other time.

Still not clear on whether the truck MAF is the
SLP MAF (minus resistor) is the Z06 MAF, but the
"fall off the cliff" scenario isn't there for
mine, by a long shot.

Team ZR-1

At idle your engine is around 40-45 KPA engine load, so it would be
around 2700 Hz, but that is not the problem, it is in DECEL, when in low trim cells and low KPA.
As I mentioned the SLP is nothing more then a stock GM MAF with a resistor and their label put in place of Delphi.

jimmyblue

iTrader: (11)

So would I see this as something like a bogus gm/sec
airflow on the Predator real time screens? I don't
have a long enough extension cord on that old Tek7904
to do deceleration testing....

Just took a quickie reading of the MAF w/ the engine
stopped, and get a frequency of 52Hz with no airflow
at all. So I guess it's a lot about how fast the IAC
lets your throttle (effective) drop, surely the 'Vette
electronic throttle gets into it too, as to whether
you would ever see the low side of 1500Hz? I gather
there's some funny engine control stuff about
deceleration control (to keep the RPM from bouncing
off the floor).

Team ZR-1

C5 does not have IAC, being its drive by wire the TAC unit is very protective so that if there was a failure the gas pedal signal is not calling for fuel.
To gain fuel mileage the PCM on decel goes min pulse width yet with a 85 mm MAF in a car designed for a 75, the LTFTs should to +25, yet it is in decel and of course then injector flow is at minimum.
This is expected since MAF is outputting less then the lowest MAF table value and the A/D value does not match what is in the table so PCM has no way to know how much fuel to add and thus on a C5 TAC protects driver by DTCing into reduced engine mode.

jimmyblue

iTrader: (11)

I checked this out a little more today and I think
this issue is something specific to the drive-by-
wire 'Vette.

Monitoring my MAF's reported airflow, I never saw
it drop below 0.9lb/min (higher when cold) under
closed-throttle, in-gear deceleration. Idle is
0.1-0.2 lb/min higher. The airflow is not being
completely choked off, on my auto SS.

Stopped-engine doesn't produce any Predator
updates but during spin-down I got an 0.3 lb/min
reading. So apparently the PCM can still resolve
lower frequencies (1/3 the airflow needed to idle
at hot) than I ever see within the driving
envelope.

LTFTs under the same condition ranged as low as
-12 (not the -25 clip value). My car has a general
trend of higher LTFTs at high vacuum / high RPM
and higher (less negative) LTFTs at low vacuum /
low RPM. Just short of flipping into WOT I have
-1.5 - -2 LTFTs.

So my conclusion is that this SLP 85mm MAF is not
putting out anything that the taxes the PCM's
ability to deal with (in my application). Your
mileage may vary....