BPC question. Can you check my math? 7060 $85

[chevmasta]

Can someone enlighten me on what this table does? what does the "fast" mean?
In the .xdf its called this:

TPS Threshold Vs. RPM For WOT, (Fast)

[Six_Shooter]

I haven't had success with BPC/BPW formulas in any tuning I've done. In every case I run out of headroom in the VE tables, and need to increase the BPW/BPC in order to get a good range for tuning.

[EagleMark]

Can someone enlighten me on what this table does? what does the "fast" mean?
In the .xdf its called this:

TPS Threshold Vs. RPM For WOT, (Fast)

The mask $85 is not complete so don't have all the parameters.
The TPS Threshold Vs. RPM For WOT is a secondary qualifier for entering into PE.
along with
TPS Threshold Vs. RPM For WOT, (Fast)
The two together are used with another TPS % hysteresis, if it moves further then the hysteresis then it is FAST and bypasses PE delay. If you set PE delay to 0 then it does not matter.

Hysteresis Pairs
Some of the constant values are hysteresis pairs. This technique is used to keep enables from bouncing in and out of a specific condition due to small variations. For example if something is supposed to happen when the TPS has reached 50%, we will set an enable threshold at 50% and a disable at 48%, this is a 2% hysteresis.

[EagleMark]

I haven't had success with BPC/BPW formulas in any tuning I've done. In every case I run out of headroom in the VE tables, and need to increase the BPW/BPC in order to get a good range for tuning.

BPW is a setting based on fuel pressure, the ECM uses it to calculate fueling in every respect. Everything starts there. You can cheat but it will always bite you in the butt somewhere else, like PE or cold start or AE or?

BPW = BPC * MAP * T * A/F * VE * BVC * BLM * DFCO * DE * CLT * TBM or whatever starts at BPW.

If you use the available calculators you'll see even GM cheated or left some room for production varibles. 61lb injectors and a 350 cubic inch engine is 140 BPW no matter what fuel pressure you use. But in the bin file they are set to 135 BPW. But if you change fuel pressure the BPC changes but not BPW! Part of EFI self correction but it has to be close...

Problem is when you increase pressure and calculate BPW it's just one part. The next is the injector bias.

Added to the total BPW. used to compensate for injectors that open slowly. As the fuel pressure is increased the injector takes longer to open. If you add fuel pressure this should be increased.

So in this case BANC has an injector bias of .27... the XDF may be off a point as all others I've seen are .27x so the resolution is off.

But fuel pressure changed from... who knows? Another controversial subject. Since his BPW was 142. There's always a possibility of up to 10% difference in injectors as well, this may be their built in calculation. Or possibility of fuel pressure differences in a production car! Calculating BPW for 80lb injectors comes out to 139 at 12 psi, so we will go with fuel pressure of 12 psi because it keeps BPW and BPC calculations very close to each other BPW 139.05 to BPC 140.37. Running more pressure or less pressure spreads these numbers apart.

80lb injectors from 12psi to 16psi changes BPW from 139 to BPW of 120.41

Then need to add pressure change to Injector Bias.
16/12 = 1.333 difference x 100 to convert to % = 133% take Injector bias of .27 x 133% = new injector bias .3591 or .36 rounded.

And there's your missing fuel!

[chevmasta]

That was very informative.........I learned something!

I've never really heard of changing injector bias reading various tbi tuning threads on the net.

So tomorrow, I'll change the BPC back to 120, change the injector bias to .36 and retest!

I think that the BPC calculation spreadsheet should incorporate the injector bias calculation also. Why haven't we done that if it's so necessary?

Just for grins.......here's my BANC.bin that was read with an HDR1 from my Memcal.

[Six_Shooter]

I know the math used inside the ECM, that's not what I'm referring to.

There are a couple formulas floating around that is supposed to give you the value of the BPC/BPW, based on a few variables, that include injector size, and displacement. I have found that they calculate too low and I end up setting the BPC/BPW by feel anyway.

[EagleMark]

I've never really heard of changing injector bias reading various tbi tuning threads on the net.

Can't believe all you read on the net...

Have you ever read were 5.7L injectors are 55lb and Cop Car injectors are 61lb? That was wrong when the Internet rumor started years ago but people still preach it as gospel truth?
http://www.binderplanet.com/forums/s...00&postcount=2

How about catalytic converters are designed for 14.7 to 1 AFR? Or narrow band O2 sensors adjust to 14.7 AFR? Did you know your AFR gauge will read 14.7 to 1 AFR when it's 13.9?

[EagleMark]

I know the math used inside the ECM, that's not what I'm referring to.

There are a couple formulas floating around that is supposed to give you the value of the BPC/BPW, based on a few variables, that include injector size, and displacement. I have found that they calculate too low and I end up setting the BPC/BPW by feel anyway.

I've done some serious testing on changing BPW as a tuning tool and you can fudge some, I'd have to get better at reading code to find out why it goes to hell after to big a change? But it seems to be OK to add about 10 off from calculated fuel pressure and change BLM straight across the board. Then it just goes goofy after that, BLM go rich at idle and lean up top? Same thing if you take away 10... AE and PE both show changes in WB readings that were steady before the BPW change. It took a perfect tune and datalogs to actually verify. No way to find it without?

[chevmasta]

Can't believe all you read on the net...

Have you ever read were 5.7L injectors are 55lb and Cop Car injectors are 61lb? That was wrong when the Internet rumor started years ago but people still preach it as gospel truth?
http://www.binderplanet.com/forums/s...00&postcount=2

How about catalytic converters are designed for 14.7 to 1 AFR? Or narrow band O2 sensors adjust to 14.7 AFR? Did you know your AFR gauge will read 14.7 to 1 AFR when it's 13.9?

Being new to the TBI scene I haven't read ALOT. 2 kids and the inability to access interwebs at work don't help either for research. LOL

I understand the AFR's........errr we should really be talking lambda. Hence why I want to get my LC-1 installed.
I had a wicked 528hp Subaru STi....so I'm not new to the "tuning" scene...just the first time for me to actually adjust this stuff inside the computer. That car ran 25psi of boost......about 11* of timing at peak torque, and 19* at 7800 :) (water/methanol injected.....and I ran some pretty high EGT's when really holding my foot into it for awhile). 12:1 AFR
Go ahead and figure out lambda with 92 octane E10 with a varying rate of 50/50 water/VP Racing fuels M1 methanol injected 30psi of spray through a .040 nozzle at 11 psi boost pressure...........and a 100psi of spray through the same nozzle at 18psi of boost pressure.......that's why i left it up to the professionals to tune my STi. haha

[EagleMark]

Found the exact formula in the hack and the reason the calculators are off by a little. 5.7L injectors are rated at 61.2lb/hr.

  TBI 
     ;   Val = 1461.5  * (VOL/RATE)
     ;           VOL  = Vol of 1 Cylinder in liters, (0.7125 L)
     ;           RATE = Injector flow in gms/sec
     ;        5.7l = 7.71 gms/sec (61.2#/HR)
     ;       (VOL/RATE) = 0.0924 l/gm/sec 
  ;  Note:
  ;  1. Cyl VOl is for a single cylinder in Liter's
  ;  2. Injector flow rate is in in grams/sec

So the 135 in 5.7L is accurate.


The hack for $85 7.4L

     ; TBI 
     ;   Val = 1461.5  * (VOL/RATE)
     ;           VOL  = Vol of 1 Cylinder in liters, (0.925)
     ;           RATE = Injector flow in gms/sec
     ;        7.4L = 9.52 gms/sec (75.55#/HR)
     ;       (VOL/RATE) = 0.09716 l/gm/sec

Which ends up at BPW 141.99934 and exactly what comes in $85 bin.

So it looks like 80lb/hr injectors are 75.55lb/hr ? EDIT: Wrong, they are 74 lb/hr injectors.

[chevmasta]

Well I guess that puts an end to any mysteries! haha

[EagleMark]

EDIT: Wrong, see post
http://www.gearhead-efi.com/Fuel-Inj...ll=1#post19879

[chevmasta]

I remember reading people saying there's 80 and 90lb/hr 7.4l injectors. (maybe the 90lb ones were the high pressure ones?)


I went and did a couple hours of tuning just now. With a BPC change to 120 and a injector bias change to .36 I found I was still globally lean? SO IDK WTF to do.

So I put my BPC and injector bias back to the stock settings.....and I did some tweaking on my old VE map. I found that my BLM's were in the 135 range up top. So I added some more fuel but am still maxxed out at 99.xx in the VE table. I guess I'm going to have to make a fuel pressure increase again? This is a stock 454 engine with headers and a 3" exhaust is all. Weird that it would be lean from GM?

I also found about 5 counts of knock where the PCM pulled a little timing. these are low rpm/high load areas leaning on the TCC. So I've been comparing my stock BANC.bin to my map and in some area's I'm back to stock level timing.

I pushed the truck today. Running WOT a few times to view for any KC. I didn't get any. I can tell you that this truck has massively woken up via the butt dyno. Alot of that is probably the PE delay getting zero'd. It overall pulls much stronger that it has over the last several years. Even with 217k on it. LOL

Here's my BLM history table:

[chevmasta]

I do have headers now and have been reading about increasing the INT delay. Any suggestions as to how much? 50ms/ft of increased length? This O2 sensor is about 3" back farther in the pipe than my OEM one.

[EagleMark]

That's not bad BLM numbers, but if your hitting 99% in VE tables it's already to much. YOU NEED MORE FUEL!!! Add pressure!

All the BPW calculators won't help if you insert wrong information. No use inserting 80lb/hr injector since the origanal BPW was based on 75.55? If you use 80 BPW comes up as 139, but the grams/second are wrong... if you enter 75.5 the BPW is 147 and grams/second are still wrong...

I'm learning a lot here because of this! Like we need somone with actual math skills and spreadsheet calculaters that work.