Very unusual '7747 .bin ~ 7.4 liter / 700R4

[dave w]

There's also 2 wires swapped on BB IAC! never figured that out either why same ECM and parts but 2 wires swapped on BB. Your truck has also had an IAC plug change, that truck harness came with sqaure plug IAC.

All wiring diagrams floating around are SB and don't show the change. I had a pdf with the 2 swapped on my dead laptop, we'll see how much I got before the reformat...

Good thinking on the IAC wiring. I'll investigate the IAC wiring tomorrow. I'll use the '7747 wiring diagram for a 454 and use an ohm meter.

The attached .xdl is after changing the injector bias a small amount. I noticed the INT are better, but at the beginning of the data log it looked like all the BLM's were going to rich. Then at the end of the data log, the BLM's changed to near normal or slightly lean.

dave w

[EagleMark]

Good thinking on the IAC wiring. I'll investigate the IAC wiring tomorrow. I'll use the '7747 wiring diagram for a 454 and use an ohm meter.
dave w

Post up a diagram if you can.

The attached .xdl is after changing the injector bias a small amount. I noticed the INT are better, but at the beginning of the data log it looked like all the BLM's were going to rich. Then at the end of the data log, the BLM's changed to near normal or slightly lean.

dave w

No attach? Did you change BPW back to calculated value?

Rich at beginning and better at end, if it was warmed up the whole time I would say you didn't disconnect power to loose the BLM learn and it was correcting from what it had before the injector bias change? With engine warmed up and driven, kill power to ECM, start and when goes closed loop do quick data logs just a few minutes. Three runs at 20% TPS, 40% TPS and 60%TPS, adjust VE, smooth table rinse and repeat! Use the wire frame view to finish shaping/smoothing Main VE Fuel Table. Really sped up building a VE table for me.

Back to BPW calculated value. This is what has happened every time I test changing BPW from that value, weird things happen high and low from where you were. I did this on a stock truck/engine with a perfect tune. Increased BPW and bottom end got rich and top end went lean. Why? I don't know but it has happened every time every vehicle. Next time I think I'll try the opposite and decrease BPW to see if BLM goes opposite.

HTH!

[RobertISaar]

Increased BPW and bottom end got rich and top end went lean. Why? I don't know but it has happened every time every vehicle. Next time I think I'll try the opposite and decrease BPW to see if BLM goes opposite.

the answer to why is one that requires you to be familiar with the way GM calculated a BPW from the BPC based masks.

the short answer is that moving the BPC is one direction will cause the table values to spread out more than reality while moving it in the other direction will cause them to group closer together. let's say with a stock VE table and stock BPC value that you see 20% VE in the weakest part of the table and 80% at peak torque. based on what you've stated, moving the BPC upwards will cause the values to spread apart(now something like 15% and 85%). a small decrease should change them to 25% and 75%.

again, that's the short (and simple) answer, but it's accurate.

[dave w]

the answer to why is one that requires you to be familiar with the way GM calculated a BPW from the BPC based masks.

the short answer is that moving the BPC is one direction will cause the table values to spread out more than reality while moving it in the other direction will cause them to group closer together. let's say with a stock VE table and stock BPC value that you see 20% VE in the weakest part of the table and 80% at peak torque. based on what you've stated, moving the BPC upwards will cause the values to spread apart(now something like 15% and 85%). a small decrease should change them to 25% and 75%.

again, that's the short (and simple) answer, but it's accurate.

Robert, I've never fully understood the BPC vs. VE workings. Thank you, your explanation helps!

dave w

[EagleMark]

the answer to why is one that requires you to be familiar with the way GM calculated a BPW from the BPC based masks.

the short answer is that moving the BPC is one direction will cause the table values to spread out more than reality while moving it in the other direction will cause them to group closer together. let's say with a stock VE table and stock BPC value that you see 20% VE in the weakest part of the table and 80% at peak torque. based on what you've stated, moving the BPC upwards will cause the values to spread apart(now something like 15% and 85%). a small decrease should change them to 25% and 75%.

again, that's the short (and simple) answer, but it's accurate.

That would also explain why it is so important in this mask to keep BPW calculated properly and also explain why there is 2 VE fuel tables. Look at VE1 and it is very low resolution so with BPW not being correct the spread is to far.

This week I did another 7747 truck and from boredom used both VE tables. VE2 set to 30% and the tune went smoother then usual? Because I am so used to tuning this ECM? Or because I spread the low resolution load? Just thoughts but I think I'll use this method again. Although using the BLM spreadsheet is not as accurate in VE1 as it is not 100% of calculated fueling anymore.

[RobertISaar]

since VE1 and VE2 are combined to form a single 8 bit value, there is no difference in resolution if you place the values in either one, so long as it adds up the same.

if you want the most possible resolution using stock code.... you would setup the BPC so that the lowest VE cell has correct fueling at 0% and the highest VE cell has correct fueling at 100%. that's VE1 and VE2 combined.

as you can imagine, this scenario is kind of unrealistic, since 0% VE would be a BPW of 0.

so, in a real-world situation, best resolution would be achieved with allowing the highest VE cell to touch 100% while retaining a correct AFR.

[EagleMark]

Dave, I noticed Async fueling at idle in your log? Also INJ - Async Transition Lo and INJ - Async Transition Hi are not stock 7.4L settings? Also not 5.7l settings?

The Async flag goes off when Off Idle. Not sure why your getting Async Fueling at idle? Most of my time has been in SB and Async only comes in WOT high load situations... and doing a recent six cylinder conversion using a V6 bin to start was always Async? Don't have my files from dead laptop so can't look at any old BB logs...

[dave w]

Dave, I noticed Async fueling at idle in your log? Also INJ - Async Transition Lo and INJ - Async Transition Hi are not stock 7.4L settings? Also not 5.7l settings?

The Async flag goes off when Off Idle. Not sure why your getting Async Fueling at idle? Most of my time has been in SB and Async only comes in WOT high load situations... and doing a recent six cylinder conversion using a V6 bin to start was always Async? Don't have my files from dead laptop so can't look at any old BB logs...

I noticed the Async also. I've been thinking the tune is not close enough yet to be concerned about the just Async yet.

Thanks for thinking about the IAC wiring, as you suspected it is not correct. I also suspect the IAC is faulty. I don't think a faulty IAC circuit will trigger Async, but it's best to fix the IAC and see what happens.

I'll get back to tuning on this Suburban in a day or so, need to fix the IAC.

dave w

[PJG1173]

Post up a diagram if you can.

I found this on another site a couple of weeks ago while wiring my conversion up. it show's the two wires swapped for the BB TB.

[dave w]

I found this on another site a couple of weeks ago while wiring my conversion up. it show's the two wires swapped for the BB TB.

I have a used factory 7.4 liter '7747 wiring harness I used an ohm meter on. Using the orientation that the 454 IAC connector is plugged into the throttle body;

Top of IAC Connector
LT BLU / BLK C6
LT BLU / WHT C5
LT GRN / WHT C4
LT GRN / BLK C3

dave w