VE BLM tuning via Dave’s spreadsheet

[dave w]

TBI injectors fire into atmospheric pressure air, correct?

Yes.

I was thinking about the vacuum referenced fuel pressure regulator Turbo City used to sell.

dave w

[RobertISaar]

that would be why. gm uses a vacuum referenced FPR to keep the injector flowrate consistent when injecting into a vacuum. it also keeps the injector characteristics predictable.

[EagleMark]

Here's my take on the VRFPR on TBI.

As fuel pressure rises from stock the Injector Bias needs to be adjusted as well, but most guys don't? I just take the % of fuel pressure raise and add it to bias. If your adding 50% pressure from 12 PSI to 18 PSI then Injector bias changes from .396 to .594 is a lot of fuel! But the real purpose is as pressure increases it takes longer for injector to open...

If you work with the injector bias as you raise pressure it all works well to about 20 PSI, after that idle fueling starts to suffer, you may need Open Loop Idle. There; also a Idle AFR bias and Idle OR correction error...

After 22 PSI the VRFPR works really well! Idle is a PIA here, but then doing VE in the small resolution $42 table sucks! This is where you really need VE1 and VE2 so add 20% to VE2 and you have to get Dave to fix the spreadsheet cause I hate doing math cell by cell!

You know how I set BPW...

When you need this much pressure there's obviously something done to motor! Many other things need to be adjusted for it before you can work VE fuel. Things like INT delay has to be fixed for headers. Proportional gains has to be fixed for cams, fixed anyways in a lot of bins.... BLM learn tables need to be adjusted so idle and low RPM are not in same cells. Spark advance table needs a more performance oriented attitude before you start all these, then work on VE fueling.

[dave w]

I was thinking, maybe the name Vacuum Adjustable Fuel Pressure Regulator (VAFPR) is more accurate? My testing shows that the TBI VAFPR I have will be about 12 PSI at idle (near stock pressure), then at 70Kpa ~ 100Kpa the VAFPR pressure will be about 14.5 ~ 15 PSI. The vacuum hose for the VAFPR is connected to manifold vacuum, same vacuum source as the MAP sensor. The VAFPR works great for a 7747 application that needs near stock fuel pressure at idle, and a few extra PSI of fuel pressure for higher RPM's.

dave w

[EagleMark]

I've never tried at that low a pressure but that would be sweet to kick in same time as PE!

[majacoby]

28 Jan VE1 chart.jpg28 Jan hist Avg bpw 140.jpg

Here is what I got after going back to a smooth VE graph and setting Base Pulse Width to 140 and then making 2 runs and adjusting via Dave's spreadsheet. I thought it was interesting that I had three 128's in the top ranges.
The VE1 chart and graph are after using the history table at the bottom.
I'm still going to get around to the fuel filter and pressure adjustment. I'm kind of busy. Rebuilding a John Deere 4030 diesel and putting and addition on the house. I'll get to it...

[EagleMark]

Your still out of fuel. Look at VE 90 MAP 2400 RPM is 99.xx% and BLM are still 137...

[dave w]

I agree with Mark, the higher RPM's are needing some additional fuel. I'm glad to see 140 BPW has the lower RPM's back closer to 128.

dave w

[majacoby]

OK guys, I finally got time to adjust my fuel pressure. I modified the regulator and rebuilt the TBI.
If the stock one was running at 12 psi and I raise the adjustable to 14 psi, do I need to change any thing to run and start data logging again? I know it's always safer to go rich instead of lean.
MarkJ

[dave w]

OK guys, I finally got time to adjust my fuel pressure. I modified the regulator and rebuilt the TBI.
If the stock one was running at 12 psi and I raise the adjustable to 14 psi, do I need to change any thing to run and start data logging again? I know it's always safer to go rich instead of lean.
MarkJ

I would set the adjustable pressure regulator to 14 psi and then go data logging test drive.

The data log will help figuring out where the BLM's are Rich / Lean, then we can make adjustments as needed.

dave w

[EagleMark]

I would set the adjustable pressure regulator to 14 psi and then go data logging test drive.

The data log will help figuring out where the BLM's are Rich / Lean, then we can make adjustments as needed.

dave w

13-14 always seems to run better then even 12. You can always tune down fuel in VE tables. You can't add what is not supplied in the first place.

[majacoby]

Will do! After I get my replacement fuel lines..
Thanks Dave and Mark.

[delcowizzid]

you shouldnt need a vacuam referenced reg as the injectors arnt in vacuam in a TBI TB are they.if above the throttle blades should be a fixed reg unless boosted

[dave w]

you shouldnt need a vacuam referenced reg as the injectors arnt in vacuam in a TBI TB are they.if above the throttle blades should be a fixed reg unless boosted

The TBI vacuum referenced regulator seems to cause confusion? Simply stated, the TBI vacuum referenced fuel pressure regulator adjust fuel pressure to the injectors only! The injector fuel pressure has absolutely nothing to do with where the injectors are position (atomsphere )! At idle the vacuum referenced fuel pressure regulator sets the fuel pressure at a MIMIMUM fuel pressure. At Wide Open Throttle the vacuum referenced fuel pressure regulator sets the fuel pressure at MAXIMIUM fuel pressure. A performance modified TBI engine needs less fuel pressure at idle and more fuel pressure at Wide Open Throttle.

Another way of thinking about a vacuum referenced TBI fuel pressure regualtor works is to think about injector flow. My testing showed a 61 lb injector flowed 61 lbs of fuel at idle, and nearly 68 lbs of fuel at Wide Open Throttle. A TBI engine making 1 HP per cubic inch or more needs help with injector flow at both Idle and Wide Open Throttle RPM's.

dave w

[RobertISaar]

controlling fuel pressure via vacuum in an application that doesn't fire the injectors into a vacuum WILL give more dynamic range.... but it also causes the injector to be non-linear(or to be more accurate, more non-linear).

it can certainly work as an advantage to an engine that needs it, but now a 5mSec burst of fuel at 10kPa will be noticably different than the same 5mSec burst at 100kPa. after tweaking the calibration, it will work well, but fuel flow calculations would now need to be flowrate corrected. can think of it like the LSx engines that run a constant rail pressure, but shooting into a variable vacuum.