Well I finally got around to making my AFPR into a VAFPR, but there is a problem. I have the initial pressure set at 15psi but when I hook up the vacuum line to any of the vacuum ports in the frong of the TB it dips down to 5psi at idle. There is no way possible to tune around such a swing in FP so I need some help. What kind of spring should I use? Right now it's a very short spring but heavy gauge.

 

Why dont you add a second spring in there? Enough space? It'll need to add little tension when its all together of course or that would screw up the pressure with no vacuum. Local industrial supplier here carries all sorts of springs, thats where I would look.

You could also create a leak in the supply vacuum line, though thats kind of a bad fix I think. It'd still work though.

You can also easily determine the properties of the spring you have with a scale, a ruler, and some muscle. A TPI FPR spring is around 360 lb/in. Diameter is about .8", cant find mine or I'd measure it to be sure. The housing it fits in is 1.310", so the spring could be as much as 1-1.1" OD. I can get or have all the specs if you want them. I think an extra TPI FPR spring would be kinda expensive to just go buy though, unless someone has one laying around.

 

I haven't gotten around to measuring the pressure on the spring but I did get all the dimensions. The spring uncompressed is 1.225" high, .977" o.d., .798" i.d. I can fit a 1" o.d. spring no problem (duh) and I'm taking a look at http://www.mcmaster.com/ they were recommended to me through a fellow ME students father (also an ME). I can't seem to find a spring with a heavier gauge with keeping the closed ground ends and the ~1.25" height! I might end up making my own spring.

 

Or you just put a restriction in the return line that keeps the FP above a certain point.
Costs all of 89 cents.

 

That's what a fuel pressure regulator is! It's a restriction in the return line to keep pressure at the injectors. If I just clamped off the return line and my car was at idle I would soon be looking to replace my fuel pump.
Anybody have any good inexpensive sources for machine work like handmade springs? I don't care if it's closed or closed and ground, I just need a spring made with a few certain specs.

 

Well if your stupid and you want to close off the return line completely go for it. Or you could put a restriction (ie a second FP regulator) after the VAFPR and adjust the minimum with one and the max with the other.
But it probably won't work. I've only had it that way for a few months now.

 

Aaron, tell me, where exactly do you have this second fuel pressure regulator and FYI, you can't have a "min" and a "max" because whichever is stronger is going to be your ONLY fuel pressure. The pressure won't dance around from one setting to another.
Now, back to the SERIOUS buisness end.
I finally got it done. I replaced the spring with one that is almost 4 times the lb/inch. The stock spring in the holley unit is about 22lb/inch. I had it pegged to the bottome just to get 17psi, any further and the adjustment screw would have fallen off the last thread! This new spring is a LOT taller so I had to back the screw all the way out so that the spring was sitting on the top of the can. My min fuel pressure is now 12psi which is a LOT better than 5psi with the stock holley spring.
Before the swing was from 17psi at WOT and 5psi at idle vacuum. Now it's 17psi at WOT and 11psi at idle. When I cranked it down I got 20psi and at idle it would dip down to 12psi . If anybody wants I can make their units Vacuum referenced. Depending on how many orders (springs) I can probably make them for $20 + shipping. Let me know through this post if anybody is interested.

 

Obviously you can't figure this out but in case anyone else ever does this and doesn't want to go through this, here is how I have mine setup.
Starting with no FP regualtors we have about 2psi or less on tbi.
Now we take a mallory VAFPR and put it in line. At idle it may only have 2psi because the plunger is all the way open and there is no restriction.
Now we floor it and the vacum changes and causes the PSI to go up say 15 by closing the plunger and restrictioning the return line.
Now lets say we only want a max of 15psi but need a min of 10psi. We adjust the VAFPR minimum valve at idle to 10psi but the maximum valve may go up to 20psi now because the plunger closes farther. We don't want this.
So we adjust the VAFPR to the max psi we want at WOT. In this case 15psi. Now at idle its still 2psi. So we put a second afpr after the vafpr and set its minimum to 10psi if thats what we want. At idle the second afpr is holding the minimum psi up at 10 since the vafpr is open. At wot the vafpr takes over and bumps it up to 15psi.
I don't think this is a hard concept. I can't spell it out any clearer. Now I explained myself. I dare you to back up your statement about not being able to have a "min" and a "max" one.

 

POW!!!!!!

Right in the kisser!!!!!

Makes total sense to me. I kinda figured out what you were saying the first time you posted it. I just don't know much about VAFPR.

OK. Now my question is what's the FP at say 1/4 throttle for cruizing? Like maybe 12 PSI?

 

The use of dual FPRs is mentioned on the DIY EFI web site (which prompted me to post here on the GM vFPR over a year ago). The good thing about this is that it allows the fuel pressure for

(a) idle/cruise, and

(b) WOT,

to be each tuned separately, without affecting the other. Of course, there is extra cost & plumbing involved.

The difficultly with using a single vFPR is that you have two (general) throttle conditions you want to tune for (idle/cruise, and WOT, with smooth transition between them), and you have multiple variables to deal with: spring stiffness (the spring K for you Mech Es), the spring compression preload (which is the loading on the FPR diaphragm at WOT, with no vacuum), the spring compression + vacuum load (which is the loading on the FPR diaphragm at idle/cruise), and the mechanical orifice delay used to slowly transition the removal of engine vacuum for WOT events.

That's 3 or 4 simultaneous variables (depending on how you view them) to deal with when trying to tune the single vFPR. Of course the single vFPR is less expensive, and has less plumbing, than using two FPRs.

FWIW.

 

"POW", lol, so where does one pick up SUCH a deal as this? You were NOT clear about using a second FPR with the "89 cents" comment. You can't get a ****ing hose clamp for 89 cents so please PLEASE tell me why I'm the only person on this thread that's following things from the beginning?
Should I have assumed you were talking about using a second FPR when you said 89 cents or was that some kind of inside joke.

Thank you for finally making some sence. That method would definatly work very well for me, I just can't afford a second FPR, even if it does cost $.89 .
Did you just install the V.AFPR in the return line's flex (rubber hose) section?

 

I'm glad you took that the right way JPrevost. From what I've seen in other threads you're easy to irk.

I imagine that some type of a simple shut off valve would work. That way you can open/close the valve until you get the desired "lowest" pressure.

I've heard that some guys use a similar method for 1/4 mile runs. They just clamp the rubber hose near the tank, or pull it off and plug it so the pump is giving all the pressure it can. Then you just undo it when you leave.

I don't know if it's worth anything. It could be, since the TQ lock-up trick helps. I would have never thought it would.

 

It took me only 1 datalog with winaldl and one new burn to nail down the fuel curve with this new spring! It's running BLMs between 126 and 130, I couldn't ask for any better out of my stock fuel pump and crappy holley injectors. Oh yeah, did I mention that my o2 sensor is a heated element version that's not heated and is only reading off of the number 1 and 5 cylinders (strange, but it works).
The pump shot is back to stock because the fuel pressure change alone is plenty to prevent a lean hesitation.
Oh, and about that 89 cent afpr, I have one that's better. How's FREE, just changed the spring which was free from a friends father. 17psi and now only 12 psi at idle, couldn't have asked for any better although it would be cool to have a set FP up until 90kpa then from 90 to 100+ the fuel pressure would go up.