liquidh8

What would be the best to tune the VE tables with the VAFPR. set @ 13psi idle, 20psi WOT. I'm just seeing the blms go all over the place with this regulator. Stab the gas, they go way down, 98-105, once you get to speed and stabilize. the go up to like 122. It's just that it takes a while for it to get to that 122 with the same kpa and rpm's, am I missing something?? Thanx all

JPrevost

Yeah you're missing something.... VAFPR's don't work well PERIOD. How can they? The ecm does it's fuel calculations based on a fixed injector size, it crunchs numbers to come to a pulse width. Now what if that injector size changed. Well to put it simply, your ECM is on crack.
I've tested the VAFPR's and never, EVER, have they run better than a properly setup eprom. Infact it would take me almost 2 weeks worth of weekends to get things within reason but even then the car would do like you said, BLM's swinging all over the place no matter how much VE table adjustments I made, it never got really good. My best was BLM range of 114-136. Let's not even talk about the AE. All those transients are again worthless because they are figuring that the injector flows x amount of fuel at x pulse width. Where as now you've got injector flows x*sqrt(old pressure/new pressure) for the same commanded pulse width. AE just goes all to **** and that is why your BLM's are dropping like a rock then coming back up. You might try and take the AE table and just flat line it as in don't make it increasing. Just fill the whole table with a value and go try it out, that's how I got it to not be so bad... then I wised up and tested the theory of "my idle pulse widths are too small"... it was debunked in my book because I had no problems with running 28psi on 65# injectors at a 650rpm idle. Smooth, almost too smooth so I kept the Borla exhaust cut-out open most of the time. Passed the sniffer 3 times (failed for other things) without EGR every time. 2nd time I was getting a little close on the NOx so I ran it richer by adjusting the closed loop PID tables (expert only) which cooled down the chamber with engine temps at 210 and HC went from half the limit to 2/3 but NOx went way down.
So my advice is to set it and forget it. Go to 20psi if that's how much fuel she needs at WOT to keep from going lean and then set the bpw constant accordingly, then adjust VE tables, while messing with the spark and AE. When adjusting the VE's after a fuel pressure change, run conservatively on the SA table. As you sneak up on the SA you will most likely see the BLM's showing you a new direction meaning go back to the VE after some SA tuning. Do this and you should have a strong running smooth TBI engine.

liquidh8

Thanx JP. I'll do that then. I'll disconnect the vacuum line and try it from there. I had the 90 pph set @ 13psi with a 100 bpw, and it didn't like @ WOT. So, I'll take it to 20 psi all the time, and leave the BPW (?), and tune from there.

BadDog

Funny, I've been pondering this in the last few days. I originally ponied up for a VRFPR for my K5 project. Then the more I read here, and look at the tables in TP, and try to figure out what it all means, I came to the conclusion that VR is just going to confuse the heck out of things. My current thought (I don't know enough to have opinions yet) is that VR is at best a "crutch" for dealing with modified engines running a stock ECM. Turning up the pressure helps deal with the tendency to lean out and wakes up the upper end when in PE, and the lower idle/no load pressure keeps you from going too rich on the bottom. But at the cost of confusing the crap out of the ECM in the middle (not in PE). As a result, I had already decided to ditch the VR and run it as a standard adjustable FPR.

Fast355

iTrader: (2)

I use a VAFPR and with some work it can be made to do just fine. Then again I am not auto-crossing! BLMs are in the 124-132 range for me, which is close enough. I had the VAFPR from the start, when I started tuning I just left it in place and tuned around it. Turns out that it works great. Then again I have 32 PSI of fuel pressure into 68 lb/hr injectors and have to pass smog. At idle the fuel pressure is roughly 22 psi.

My 305 has a smooth idle (@ 700 RPM), pulls great, gets good mileage, and passes DFWs strict Air Care dyno smog test with ease, without catalytic converters and a L82 cam.

The GM VAFPR was/is used with the HT502 TBI engine conversion package, along with a custom EPROM. It runs good and seems to do just fine in power/mileage and is emissions legal in all 50 states.

VE tables aren't all of it. The open loop A/F mixture vs. MAP table plays a huge part in tuning for the VAFPR. You can basically adjust this table to get the A/F mixture near what you want by calculating the changes in this table as it changes the BPW. Worked well for me. Only needed some small tweaks in the VE table.

JPrevost

It can work but it's a hassle when you don't need it. Why lie? And from the sounds of it you never spent much time tuning it without the VAFPR... or did you?
The other thing, and I don't know how much this has an effect but truck's don't have as strick emissions requirements so it's no suprise that the VAFPR on a bbc would passed and are 50 state legal.

Fast355

iTrader: (2)

I have tuned other cars without the VAFPR, but I need it to make mine run right. The Pulsewidth becomes TOO SMALL off-idle with my combination with the fuel pressure high enough to keep from going static @ WOT and 6,000 RPM. With the PW too short it isn't fun. Any rough running is more noticeable in a loaded down truck than it would be in your F-body.

For whatever reason the standards in my area are stricter than when the vehicle comes out.

At 15 MPH
Pollutant--------------Standard-------------Reading
HC(ppm)----------------220--------------------159
CO(%)------------------1.20--------------------0.25
NOX(ppm)--------------1800-------------------708

At 25 MPH
Pollutant--------------Standard-------------Reading
HC(ppm)----------------220--------------------56
CO(%)------------------1.20--------------------0.33
NOX(ppm)--------------1800-------------------650

The carb engine would not pass without lots of alcohol and timing retard and then it only squeezed by.

RednGold86Z

iTrader: (1)

I think another "gotcha" of the VRFPR on a TBI would be the BARO correction (i.e. driving from sea level to the top of a mountain). The pressure on the tip of the injector can change, while the vacuum reference pressure stays the same.

This would make the injectors flow more at low loads and high altitudes, unless the calibration was compensated.

But, if it's necessary otherwise, I'd use it. It's truly difficult to get a consistant idle with large injectors, especially in 2 injector TBI setups. As long as it's used in the same elevation most of the time, or at least in closed loop with learning, the BARO thing wouldn't be much of an issue.

VRPFRs calibration works basically the same as how the returnless fuel systems work, except inverse. Their fuel pressure across the injector changes, and they just use a calculation/lookup that corrects for it. If you can compensate in the VE (vs MAP), AE (flatten it as JP says), and OL AFR (vs MAP), and any other places that typically assume constant fuel injector flow rate, then it should all come out correct or close enough in the end.

va454ss

iTrader: (1)

http://www.efitune.com/forum/index.p...=ST&f=17&t=98&

BadDog

Now that is very cool. I wish I had anywhere near the knowledge to figure out how to adapt that to a 7747. But for now, I'll be content to leave mine non VR while I try to learn the basics. Then maybe I'll go back and revisit this.

BTW, how do you calculate the adjustment factors? Particularly with a custom VRFPR (modified, aftermarket, etc.)? Do you just experiment with multiple PROM mods?

JPrevost

Yeah, basically you have to go on your own and experiment.
VE table is no longer a true or even CLOSE approximation to the actual air flow. Some might say, hey, that's not a big deal because it's still getting the correct fuel... but not really.
Here's another reason VAFPR's with no code adjustment can give you headaches; Closed loop PID routines use the calculated engine air flow to make corrections in the fueling. How does the ecm calculate air flow? Well it uses the VE for one thing! So now your VE table is all lumping and your closed loop starts having trouble with over/under compensating for the fuel delivery. It's not a big PITA but it's one more reason to add to the list of using the VAFPR as a last resort, not first.
RedNGold, how can you say the 2 TBI injectors have a crappy dynamic range? What is your basis? I've gotten the pulses to be VERY low without having issues that some are saying occur. The TBI injectors fire twice as often as port injection batch fire so it's not like the pulses are far and few between that would cause a swinging AFR.
How many have you actually tuned without the VAFPR?
This past weekend I got a friends 305 TBI zz4 cammed RPM intake/spacer to idle rock solid at 650rpm with 90# injectors at 20psi (2psi below bottoming out the spring). I didn't need to run this pressure but I figured we might as well try it and see how it does... it's great. Our AE problems that were existant with the small stockers has been completely eliminated. I feel the ultimate test for a tune is to get in a high gear, ultra low RPMs, low speed, floor it, let it pull 500rpm then clutch in and come to a complete stop quickly. This tune was the cats meow, no backfire and rock solid idle... with 90# injectors closed loop at 20psi on a 305

BTW; Embeded lockers TBI code has the VAFPR bpw modifier table for when you TRUELY need it . I'm going to be making over 400hp on my next engine build so we'll see how it works out. I hope I don't need it but if I do, shouldn't be an issue with the proper code.

va454ss

iTrader: (1)

I haven't had that problem either.

So, will the Ultimate TBI code do the calcs for you? In other words, plug in the fuel pressures and it calculates the BPW for you to use in the vac reg compensation table?

As I understand it, the chip included in the GM 502 retrofit kit has the vac compensation. Ken incorporated a lag filter to smooth the transition.

JPrevost

It is a BPC vs Vac table so this take Baro into compensation. If it didn't it would be called BPC vs MAP . RBob's really smart like that.
To setup the table, I would think you just need to measure the pressure at differen't manifold vacuums and then recalc the BPC with the new fuel pressure using the formula; x*sqrt(new/old)
If RBob has a better way I'm sure it'll be described in the documentation that is released with the Embeded Lockers.

va454ss

iTrader: (1)

Easier said than done. A helper is a big plus

RednGold86Z

iTrader: (1)

Just 2. Only one had a problem. It was a 330 hp Vortec (well, an old 250hp target motor with Vortec heads, so he calls it a 330hp Vortec since it has the same parts) on 90s and using junkyard injectors and a 7747. It was a closed loop thing on that one I think. We also tried it with our aftermarket ECU. Actual PWs (including turn on time) were getting to less than 1 ms.

BTW, the injectors fire half as often PER cylinder compared to batch (once per intake stroke). But the injectors are 4 times as big.

Another BTW, I've tuned a few hundred single injector 4 cylinders (over 1000 are using my calibrations, I had my hands on a few hundred), most are <=1.6L with a 45pph injector. They have trouble idling as smooth as a carburetor when in closed loop (and no ignition control). For that injector PW's had to be >1.3 ms for stable closed loop idle. Some got away with less, but not consistently.

Async for low PWs can help. Some don't like it. Others need it. On TBI the plenum, wall film, and TB wall film can act as a nice buffer to keep the AF steady enough.

JPrevost

Maybe it was the junkyard injectors at fault. Not flowing equal.
BTW, TBI injectors might be large but they're also low impedance peak & hold. You can get them to fire very low opening times and still flow. I consistantly go below 1msec, not by much but it happens frequently. I commonly register .9ms at 650rpm idle warm. .6-1.2ms cruising depending on mph and gear/rpm. The lowest I've gone without a hitch has been .4ms, never had to go lower on any of the engines I've helped tune.
If you're having trouble idling in closed loop maybe you need to use better code or better injectors/drivers.