91chevz71

Hey everybody-
So I have a new gmpp 350 ho going into my truck (yeah i know, this is a car site) and will have issues tuning it. Tons of knowledge on this site!!! I've been reading over the diy-prom pages (results of searching for 747) and have a few questions about the constants and tables. I think I found the right stock bin and xdf filesformy truck ('91 L05 with a 700r4 w/7747)- arju.bin and $42.xdf. I'm using tunerpro to look at the info. Just talking about basics, for now...
Main spark bias- initial timing value? sort of i think
bpw constant- injector size (i calc'd 122 for 68/lb inj's) stock is 135

I understand the ecm will make changes with the amount of fuel dispensed to achieve the proper afr(is that right?). It also reads the VE tables to dispense fuel(?).
open loop= cold start, no O2 data, computer is getting fuel numbers from the main VE table. during initial start/idle, the iac is controlling the idle through steps, trying to acheive the target idle rpm in the target idle rpm/coolant temp table. The iac is also using it's steps vs. coolant temp table.
When does the computer go closed loop? Is closed loop triggered when the min MAP for BLM value constant is met?
BLM=block learn multiplier (adding/taking fuel to meet 128)
INT=integrator ( a fine tune of blm?? dunno)
what is the difference between the two? Are they running in open and closed loop? The only field I can find in tunerpro for my bin and xdf is in the constant section, and they are Min and Max integrator value. I didn't see anything about INT's in the tables. This leads me to believe that the int's are what the ecm uses to change the blm's to meet the blm desired value in the table. I've read that a 128 is the target for blm's. (my BPW constant vs. airflow vs. egr d.c. table has pretty much 123's everywhere).

What's the difference between accel enrich and power enrich? do they both use async delivery?

I know this is a huge bunch of q's, I'm trying to chew on this stuff.
Can one of you guys give me a kind of down and dirty on which tables and constants are the big ones to work with? Kind of how they work together? Like I said, I've read every thread with the term "747" in it and have found a ton of useful little bits of info, but I kind of need a description of how all the tables/constnts fit into the big picture.

Extremely appreciate your guy's knowledge and advice!!!
Mike

off to read more articles

91chevz71

it's me again-

I don't really need an engine theory 101 , just a kinda explanation of what to start messing with in tunerpro and what the relationship is between open/closed fueling and AE vs. PE vs. normal, all that stuff.
I understand the curves for everything like timing, VE, knock retard, main fuel tables. Just a little cloudy on the whole open/closed fueling thing. Why so many tables and constants for them?

cmitchell17

Im with you Ive got a 95 1/2 with a stock LO5. I just ordered my chip burning stuff. If I ajusted my fuel pressure I can take my stock injectors 55lbs/hr and adjust them for a higher presure and put that value in my chip right?

Fast355

iTrader: (2)

It will throw off the VE tables some, but it will get you alot closer by correcting the pulse width in the .BIN.

BTW, your stock 350 truck injectors are 61 lbs/hr. The 305 has 55 lb/hr injectors in it.

cmitchell17

Oh I though the 61s where in the cop cars and 55 where stock LO5.

cmitchell17

Is that why my duty cycle only goes to about 54percent at 4300rpm? Becuase im running almost 14psi.

RBob

iTrader: (1)

What Fast stated for injector size is correct.

91chevz71, head up to the sticky's, Prom Tuning Guide, section on '8063/'7747/'8746. There are a couple of articles in particular: SA logic, IAC something or other, and Fueling Logic (or names close to these). Each of those explains how the '7747 code works.

RBob.

Fast355

iTrader: (2)

Definately worth the read. Look at the TCC as well, vast improvements in driveability can be gained here.

91chevz71

o yeah, hit the mother lode of info!!!
can't believe I didn't see that eariler....doh!!

91chevz71

Ok, so I've read all the 7747 info I can get my hands on and I have (to put numbers to it) about 80% of it understood. I can't seem to find the formula for finding my new BPW constant, I'll keep looking. I have a set of 68#'s and 90#'s, so I need to find the BPW and FP needed to get max HP (330)for each set. I bought the EBL today and look forward to getting that baby cooking, and I have a couple of Q's on that setup. Tunerpro is still used in modifying bins, right? I know these are dummy dummy level questions, so bear with me. Since I don't get back to the US until November, I'm learning all I can without the truck. I goof off with tunerpro, trying to get familiar with the tables and constants. So once I have all the mechanicals in order with the swap and no leaks, etc, here's what I will start working with-tell me where I'm messing up
1. Proper BPW for the inj's
2. Get the primary VE table close throughout the RPM/MAP range (trying to stay out of AE) with VE learn (BPWmode), I'm thinking of using the stock idle control settings if they work half decent, then perfecting later on
3. get AE right through TPS/MAP amounts
4. tune SA
5. make fine adjustments to VE and AE with new SA
what else?
I have thick skin, so blast away

hopefully Rbob and other guys chime in

Thanks,
Mike

91chevz71

found the formula-
90#hr* 453.6 / 3600= 11.34 gms/sec
5.7L/8 = 0.7125L per cyl
BPC = 1461.5 * (.7125 / 11.34)

= 92
so, 92 is the new BPW constant in tunerpro (for 90#'s)
question about fuel pressure- the computer does not need to know how much fuel pressure you have, just how big the injectors are, right? It seems like the computer assumes it will always have the pressure, so I would just need to find the right FP to give me the max rated HP of the engine.?

I could be totally wrong on this..I wouldn't be surprised. lol

Mike

RBob

iTrader: (1)

Mike, I sent you an email with some additional information in it. Can use TunerPRO with the BIN and XDF along with the doc file.

Your steps list above are good. For the initial chip set up will also want to set items such as TCC (yes or no), desired idle speeds, maybe pull the timing table from your current BIN and set that up.

Then when starting disable the CCP and EGR. Once the majority of the tuning is done the EGR can be enabled and tuned. Then the CCP can be re-enabled.

Your BPC calculation is correct (92). This needs to be set in the BPC vs VACuum table. True for the ECM only knowing the injector fuel flow. If you change the FP then the BPC should also be changed.

As far as how much, is the gmpp 350 ho engine rated at 330HP? I'll use that for the example.

Using .5 BSPC (.5 #/fuel/hr/hp), and 2 injectors. First divide the 330 HP by 4:

330 / 4 = 82.5 #/hr

Then adjust for an 85% max DC on the injectors:

82.5 / .85 = 97 #HR

Having the injectors flow at 97 # hr is decent. Only need a little more. Calc the FP bump (lets bump to 100#Hr for AE leeway) and use 13 psi as the standard:

(100 / 90)^2 * 13 = 16 psi

Using 16 psi is a decent start. Then re-calc the BPC for 100 #/hr injectors.

Note that the equation I used is the inverse of calculating the flow change from the change in fuel pressure:

New#hr = sqrt(newpsi / originalpsi) * original#hr


You mentioned having a 68#hr set of injectors. To get 100#hr from those need to run 28 pi of fuel pressure. Using those along with a vacuum referenced FPR (VRFPR) would be better then the 90's at 16 psi.

The VRFPR would allow for lower flow rates at lower loads. Makes for a better running engine. The BPC vs. VACuum table would then be filled in with a varying BPC. Let me know if you go this route, I can help with the BPC values.

RBob.

91chevz71

OK, cool. Yeah, I was going to run just a AFPR set at whatever PSI required, but a vacuum adjusted sounds like it would be more efficient. I'm going to look around for how to do that- I would totally appreciate your numbers!
I want to run the 68's at a higher psi, so it would make sense having that VRFPR. It would probably run really rich (with a set AFPR)with that high PSI at low power, since the computer thinks it has 68's at the stock FP. ?

Mike

RBob

iTrader: (1)

The BPC for the 68's at 28 psi will be the same as the BPC for the 90's at 16 psi. Which is 83. The BPC is the ratio of injector flow and engine displacement.

The trick with the VRFPR is that it lowers the fuel pressure as the engine load is reduced. With the reduced FP the injector then needs to be open longer to deliver the same amount of fuel. This makes it easier to control the injector PW. And the fuel delivery is stretched out over time. Makes a huge difference is driveability.

RBob.

91chevz71

Aaaaha! Got it. Gotta find one of those....