Blackbird

I know my IFR values are correct as it's simple math to figure that out.

So I plop those in and LTrims are lean all over.

Maf is stock but by using as a push thru and being it wasn't designed as such I assume that means I may need to tweak the MAF table?

or is a stock MAF a stock MAF and leave that table alone and fix everything via the VE table?

Just trying to figure out what table to attack next. Is it MAF or VE ??

Thanks in advance.

Slowhawk

iTrader: (12)

I adjust the injector table first to get L-terms as close as possible.The math will get you close but not perfect.Then VE for minor changes.

Blackbird

the trims are off by 8-13%

I doubt the math is off by that much. I have gone that route in the past but something tells me I was just cheating by doing that and not really doing it correctly and getting the most out of the car. To get slightly negative trims I have to use a value of 5 in my IFR table. Unless I am way off that should be way too low a value for 42# injectors.

jimmyblue

iTrader: (11)

MAF table limits on a '98 are 11500Hz. By
stock cal this is about 400lb/min. Big boost
may overrun this and the MAF-reported
(interpreted) airflow will clip/limit. I read
some people just wing it, from there on up,
by PE vs RPM curve finessing. First order
of business would be to look at your raw
MAF frequency and see if you are getting
up against that limit. On my NA, no cam,
nothing special car I only see 10kHz max
which translates to about 70% of the limit
airflow. So I figure that means once you hit
about 40% (1.4X) stock output or maybe
450-500HP there is a chance you will be
flirting with this effect and have to get a
bit clever (like having a PE vs RPM that
keeps going up to override the (false)
flatlining MAF).

I believe that the MAF will have some problems
if you are push-through with elevated air temps.
The MAF works on a cooling-of-hot-wire effect,
the hot air does not cool as well, the F-body
MAF without the in-throat thermistor has no
chance of self-compensating for extra-hot
conditions. I believe this would make it prone
to report low airflow (low cooling effect). It
would be interesting to have another identical
MAF placed draw-through, just for data, to
compare the frequency error from the temp rise
in the supercharger.

Blackbird

I max the MAF by 5000 rpm. For WOT tuning I am fine. PE vs RPM does the trick well enough. What I am trying to dial in is all my non WOT situations for drivability, gas mileage, and so that trims zero out under WOT to make WOT fueling consistant.

I did do this in the past by fudging IFR but the car is sluggish when I do it that way. I am begining to think the VE is table is the next to attack but still hoping somebody that has gone thru this already will chime in.

Blackbird

anybody else?

Ed Blown Vert

iTrader: (2)

I don't understand what the issue is? My LTFT's are -2% -8 %

O2 sensors should take care of the AFR @ part-throttle

My idle and part-throttle are great. I did have to put back the MAF screen. I didn't touch either MAF or VE tables.

Blackbird

what size injectors are you using, fuel pressure, and IFR value?

I can cheat and lower my IFR value to make my Ltrims negative but I don't think that's the "right" way to do it.

Ed Blown Vert

iTrader: (2)

42's, Walbro intank 64 psi @ idle. I will have to get on my laptop to get the IFR. But I scaled them to get negative LTFT's.

Blackbird

thats what I would have guessed. if you do the math i bet your ifr value is a 20-30% lower than what the math gives you. Meaning if you calc the IFR value it may come out to 6.5 and your actually running 5.5 or lower in your IFR table to get negative Ltrims.

While I agree this technically does work, from what I have seen it makes for a sluggish car.

Ed Blown Vert

iTrader: (2)

That sounds about right, I think the numbers are in the 5's

But it runs great!

NoGo

iTrader: (2)

The injector offset curve is not correct once you change the injectors to something sizable. This error will show up by the LTerms swinging about zero. Sometimes way positive, other times (like decelleration) going way negative.

The "right" fix is to put in a proper offset curve. Being there are no offset curves for 42 lb SVO's and the LS1 fueling system, you best bet is to use the IFR table to dial it in.

Good Luck

Blackbird

very interesting.

mine are Lucas injectors but to my knowledge the offset is non existant for those too.

thanks for the info as I can now stop chasing my tail.

kp

iTrader: (34)

I used the IFR table mostly, since I'm still blow through and use no screen I had to fool with the MAF tables under 6khz to get the car to idle right since at very low throttle openings the MAF reports way less then stock for some reason. The PE tables will have to be adjusted when you move the IFR so make sure and do everything at once..

My car is far from sluggish and right now it idles/starts/drives like its completely stock and my ltrims are -5 to -10 in all cells..

Blackbird

thanks Kev -

I am going to go back to that methodology and see what I can come up with.

before I had a problem with consistancy where I would floor it and light up the tires then 5 minutes later floor it and the car is a slug.

kp

iTrader: (34)

maybe you drove over some oil

My car is very consistant and runs within .05 and .5 mph with the blower on the same day footbraking it, I bracket race it quite a bit so if it were all over the place I would know. I have right around 150 passes on the blower and its amazing how consistant it runs, hot weather slows it down a little more then I think it should but I have it pretty well dialed in using the IFR/MAF.

Blackbird

sounds good.

Time to get my rear in gear and tweak this sucka

383838

iTrader: (1)

If you're blowing through the MAF, you need to log the MAF frequency vs. LTFT's and make changes accordingly. When you're blowing through a MAF the way the air hangs to the side, center, etc. of the MAF is changed as compared to stock where it enters the MAF right out of the lid. On my truck the MAF table ended up swinging about 7% down in some areas and 12% up in others. The issue is that on my setup, yours may differ, there is a turn right before the MAF in the tubing so at part throttle and light load situations when I only see under 7psi, the air hangs to the outside of teh MAF and the internal wires do not see the air so the calculation ends up being lean. At heavy load or high boost the exact opposite was occuring where the air was moving so quickly through the turn it was actually swirling and causing the MAF to read the same air multiple times, causing the car to run rich at that time.
Hope this helps.

kp

iTrader: (34)

F1RZ06 thats pretty much what I did with the blow through, its a atraight shot into the MAF but at like 0-15% throttle (below 6khz) the MAF would read less then stock with the blower. There is a lot of air that makes it back int the MAF/TB so my guess it kind of stalls the air there. You could build a better bypass and fix it or do what I did and just play with the MAF numbers down low to equal what the stock numbers were. My Ltrims are very consistant across all the cells now, downside it takes a lot of time but I have a few ATI cars tuned that way and thay all seem to be doing OK..

S_J_H

The thermistor has no role in calculating mass air flow.It is all controlled by the 3 sensors in the maf. The thermistors on the 85mm maf's are not in any way connected to the maf electronics. The thermistors 2 wires route through the body of the maf and connect to the pcm. The pcm does not use the iat sensor for any mass air flow calculations except possibly in speed density mode.The iat sensor is used for other things but not mass air flow.
Here is GM's explanation of how the maf actually fuctions-
"Three sensing elements are used in this system.

One senses ambient air temperature and uses two

calibrated resistors to establish a voltage that is

always a function of ambient temperature. This

ambient sensor is mounted in the lower half of the

sensor housing. The other two sensing elements

are heated to a predetermined temperature that is

significantly above ambient air temperature. The

two heated elements are connected electrically in

parallel and mounted directly in the air flow stream

of the sensor housing. One sensor is in the top and

the other sensor is in the bottom of the sensor

housing. This is done so that the air meter is less

sensitive to upstream dueling configurations that

could skew the flow of air through the housing.

As air passes over the heated elements during

engine operation they begin to cool. By measuring

the amount of electrical power required to maintain

the heated elements at the predetermined

temperature above ambient temperature the mass

air flow rate can be determined."

Steve