Could someone give me the skinny on Vacuum FPR over AFPR's. What are the pros and cons. What do I do and how do I do it. Where do I get the stuff and how do I install it?

Thanks

 

Vacuum-referenced fuel pressure regulators were developed for port fuel injection. At part throttle, there's considerable vacuum in the port and intake manifold. The pressure drop from the fuel rail is considerable. Let's say the fuel pressure is 40 psi, and the manifold is under considerable vacuum--15".

That same engine under full-throttle conditions has no manifold vacuum trying to "pull" fuel from the injector once it opens. Therefore the pressure regulator jacks up the pressure when there's no manifold vacuum--to maintain some measure of the original pressure drop across the injector nozzle.

By comparison, the TBI injector never fires into manifold vacuum; since the injector(s) are above the throttle plate.

Oh, sure, some guys use vacuum-referenced pressure regulators on TBI systems, but I think it's more to crutch some other tuning or hardware-selection problem that would be better solved by using more-appropriate hardware, or better software. The typical problems are too-large fuel injectors needing lower pressure at idle and cruise to prevent the fuel curve from being pig-rich, or too-small fuel injectors needing higher pressure at WFO to prevent the fuel curve from being excessively lean.

 

That
makes perfect sence. I am running 26#'s fuel pressure with 68# injectors. It just seem to be too much at an idle.

 

The main reason that a VRFPR works so well on TBI is due to the fuel injectors alternately firing on every cylinder firing. And that they need to flow a lot of fuel.

By making the low load PW larger the fueling variance is smaller (inject to inject) and the fuel distribution is better. It is surprising how much better the engine runs.

To set one up most go to an external FPR and vacuum reference it. The stock FPR is replaced with a block off plate with the external FPR inserted into the return line. Need to be sure that a full time vacuum source is used, some on the TBI unit are ported vacuum.

Then change the BPC - BPC vs VAC table so that the ECM can calculate the correct PW.

RBob.

 

So RBob you know my car better then the rest and a VacFPR sounds like the way to go. Now tell me what to buy and how to plum it. Then we will need to do something with the EBL.

 

Everyone does it differently. It all depends upon what you want to do to do the install. The Aeromotive 13301 FPR is popular for this set up. Need to find where to mount it. Then plumb the outlet of the TBI (passenger side) to one of the side ports of the FPR.

The output on the bottom of the FPR goes to the return line. Can pick up the return on top of the engine or plumb over to the frame rail.

For a block off plate can use a 1/8" think piece of aluminum. Use the stock FPR base to trace out the shape. Then cut & drill as required. For a gasket cut the center out of the stock diaphragm and use the outer ring.

For a vacuum port avoid the one for the CCP system, that one is ported vacuum.

The calibration change in the EBL is the easiest step. Enter the values into the EBL Utility then copy & paste into the calibration. Save and flash in.

RBob.

 

I tapped into the manifold fitting to rear of TB passanger side. It feeds the brake booster. Drilled and tapped added a male nipple and it was conveniently located.

Do not tap into MAP line.

 

Rbob how does that regulator work on Vac. It has a spring and a screw. But it does have a side port for something.

 

That could be for vac line attachment to vac source. Some vafpr(Aero) have additional fuel ports. I use one to feed N20 solenoid.

 

Picture of the 13301 FPR. I labeled the ports on it. The inlet is from the TBI unit, passenger side line (return from TBI). The bottom outlet fitting goes to the fuel line that was on the TBI passenger side, it goes back to the fuel tank.

The fuel fittings are 3/8" NPT. There are a number of different ways to go to plumb the lines. From simple hose barbs and EFI line, to using -6 PTFE AN SS braided stuff. Can also bend hard-lines and use them.

RBob.

 

That is what I thought. But I don't understand the Vac. port. The regulator is a spring set for let's say 26#'s. How does the vac. lower the FPR's setting of 26#'s.
At low RPM's the vac. is high and some how that lowers the fuel pressure. and vice versa. How do you set the regulator or do you. Does the pressure just float? Or is it set at 26#'s with the vac. line disconnected. Then when the vac. line is connected to the top of the diaphram it helps the valve relieve causing the pressure to be lower? I guess if it works like that I understand it.
I'll wait befor I buy the regulator till I here back.
That will help out mt tune and MPG's. I am getting arround 13mpg now but would like better.
I can instal this this winter with out a problem I just need to get it rite in my head.

 

The fuel pressure is set by the spring tension on the diaphragm. There is fuel on one side of the diaphragm (under pressure), and air via the port on the other side of the diaphragm (also under pressure, 14.7 psi at sea level).

With the vacuum port open this setting is referenced to barometric pressure. IOW, if you measure via gauge pressure it won't vary as you climb up & down mountains (change in elevation).

When a vacuum is applied to the port on the FPR, the fuel pressure is lowered. This is due to the vacuum changing the reference pressure for the desired fuel pressure.

RBob.

 

OK I think my thinking is correct. This makes the car run better? What smoother? Idle better? better top end? quicker? better MPG? What is my goal?
The car is allready a big let down. I want it to be alot faster/quicker. I was kind of hoping for a tire smoking demon. But as of rite now I have a car that runs and is trustworthy but is none of what I expected. I know I need to get the tune rite but how long should it take?
I guess I am looking for the magic cure. I keep throwing money at the thing looking for the answer. As of rite now I am getting ready to just forget about it being the car I thought I built and ordering a new ZL1.
Am I just throwing money away? I wish I could find someone that can help me make the thing run to its potental. My excuse is always "It just needs to be tuned" then I'll be fast. I tried taking it to a pro with a dyno and they are always to busy. Then they know nothing about an EBL. I tell them I am running tuner pro and they say they have at least heard of that.
Anyways Merry Christmass

 

Basic is that it allows to obtain less unnecessary fuel at idle and light throttle, on a set up requiring "a lot" of fuel at heavy acceleration.
The more fuel the injectors are set up to flow the bigger are the adjustment the computer has to make. With less fuel to handle the adjustments are smaller and require less time to be effective, thus resulting in better efficiency. Certainly nothing to blow you of you chair, its more like upgrading, up to date with more modern EFI.

 

You set the FP to provide adequate fuel at WOT(heavy load) with a DC% of 80-85%(A/F at 12.5-12.8). Yes, the vac line is disconnected when doing so. Connecting will drop idle FP to about 15 or so depeding on amount of VAC.

 

OK then that all sounds good. Is there a way I can vac referance the fpr built into the TBI? It seems I could just add a port to the air side of the fpr. I hate to cut it up it is a good one. But that could just be a thought. The best price I've found on that external reg is 132. Then I need to plum it. I have lots of ideas how to make it look good. But...it sounds to me to be worth it. The car should run alot better in the real world. I need
26#'s of fuel pressure but only at wot. It's just more money.

 

If you haven't gotten a tune I doubt this is going to solve your problem. Do you have a wideband O2 sensor & gauge? The wideband will display your air/fuel ratio and I have seen people tune cars by driving around with a laptop and a wideband. It took him a few weeks, but once he got it dialed in it was fast.

 

There are two TBI FPR's. One I recall was used on big block marine engines that is a VAFPR. Other is FPR stock on L03 cars. Some have modified the stock by adding by silversoldering/brazing an outlet tube to it for VAC.
Ideally the BPC would be variable with VAC. For instance at WOT (0 vac) it may be 136 and at idle(65 vac) it may be a BPC of 160. Then the values for VAC other than that will follow a sliding scale.

I believe the Aeromotive 13301 has that scale published. To determine a GM VAFPR you will need to induce VAC 10-20-30-40 etc and read resulting FP. A mighty vac tool will work nicely.

ps your mask($61 etc) will need to support VAC vs BPC. Otherwise it is not a perfect result.

 

I went with "stock" set up for the stock look https://www.thirdgen.org/forums/tbi/...rfpr-pics.html

I agree with formula305 that this is not going to make your car any faster, though with 26psi of fuel pressure the VRFPR is kinda mandatory for normal driving and idling.

BTW are you tuning it yourself?

 

Yea the 13301 FPR arrived in the mail 4 days ago. Yea I know I should have it installed already but I bought my wife a new car and I have been busy. S RBob I should plug 3 of the ports and only use one pluss the bottom one for the return. Can I use one for a gauge? The fittings are going to cost me a little more but it looks straight forward. Now finding a cool spot for it is going to be a little hard. It not only has to be functional it has to look good. I'm thinking on the inner fender. I need to get the lines rite. I'm leaning towards hard lining it. Maybe some 3/8th nice blue rubber hose.
If all you out there that have done this already I would love to see pics.

 

Greg,

I ran the 13301 for several years on my Xfire Vette. W 2 TBI units ported at 2.13", using a VAFPR was the only way to get a controllable idle PW while still being able to get enough fuel to it for WOT. The 13301 came w 2 springs. I used the heavier one. At idle my FP was 10psi while at WOT it increased to 20psi.
Couldn't do this unless using EBL and BPC v VAC table. Needed 80# BB injectors. Also, w twin TBI units, I had to // plumb units so each was fed individually instead of sequentially w fuel. I connected the fuel return from each unit to the side ports on the 13301 and then the bottom port to the fuel return.
Used vacuum port at bottom of TBI unit for VAFPR. To get the values for the
BPC table, I turned on ignition to pressurize fuel line, then w Mighty Vac attached to vacuum port, I applied different vacuum to read Fuel Pressure. I used that to calc the value for the table. IIRC the BPC used the VAC Inverse, right RBob? I may even be able to find my old bins w those values as an example.

Maybe I can post pic of my old setup. I had FP gauge on TBI AND VAFPR.

 

Yes the table is VAC based not MAP. 90 MAP=10 VAC.

I too used one port for fuel press gauge. I would consider using gauge that is electroic and provides a gauge on pillar to monitor while driving. Not necessary but helpfull. Another port is used for fuel source for my N20.

 

Dug up an old EBL bin. Here's the table values I was using with the 13301 VAFPR, 80#BB Injectors. Idle was at 10psi, WOT at 20psi. Had about a 80% DC
for 280rwhp/347rwtq. AFR was at 12.8.

 

Here is a couple pics of my 13301 it is no longer routes this way but I just bolted it to the strut tower and added an extra nut ... I had to go to a local place that makes hoses and had them remove the ends off the factory hard lines and rubber lines and put them on the braided lines cause nobody makes a metric to NPT adapter and this was actually cheaper than buyin metric to an fittings then going back to NPT then NPT back to metric adapters etc ... Looks pretty good too

 

It was a lot easer then I thought. I just plumed it in at the flex hose that goes between the engine and frame.
The Vac source. Can I tap into the one that goes to the charcoal canister? The PCV is rite there too.
As for removing the adj reg. Is it as easy as replacing the regulator with a piece of aluminum and using it as a gasket? I do have an adj to Jet reg and it cost a couple bucks. Any one use it? Pay for shipping and it's yours.

 

Can't use the one for the CCP system, it is ported vacuum. Not a good idea to tap into the PCV line either. Need a dedicated vacuum source so that the fuel pressure tracks intake manifold pressure accurately.

That is what I do. Cut the center out of the original diaphragm to use the outer ring as a gasket.

RBob.

 

Thanks. What about the power brake booster line? The VRFPR is all done now I am going to reprogram the EBL. Wow that was easy. Looks good too.

 

If your using the small block TBI this should help:


If using the big block TBI, I had to drill out the vacuum port as it was in the casting but not drilled from factory. I drilled 1/8 npt fitting on the front and got a vacuum fitting so I could attach a hose.

 

Yep. Did the same thing w my single bore Corvette TBI.

 

I used the brake booster fitting at manifold. I tapped into it and added a brass nipple.

 

I am thinking that too. I have the booster and the MAP coming off the same port on the manifold. Is that ok?

 

I am tryin g to enclose pics of the install. It turned out well. Looks good. How do you install the big pics?

 

MAP needs a dedicated source...

 

Didn't know MAP needed it's oqn. Was sharing with breaks. Now can I get away with the vac source for the fpr coming off the TBI rite bank as per the pic above. IU onlt have the passenger side the other side isn't tapped.

The back of the TBI only has one tap. I am using it for the HVAC. The manifold tap I am getting the breaks and MAP.

The front I have the PCV below that the canister. and only one tap for the sides but only one tapped. I am using that for the FPR.

With the vac attached the fuel pressure only drops the 18 or so from 26. Does that seem rite? I don't see how it can go much lower. The spring is rated from 21 to 35. I have it set for 26#'s which is what the utility program says I need.

Well on a good note Happy New Year

 

 

yes. My aeromotive spring is set to 21 and is pulled to 14.5.

 

Haven't driven the car yet but it is all installed. I sure hope it makes a differance. It makes perfect sence to me.
I have it getting it source of vacuume from the passenger side of the TBI. I have it set for 26#'s and at an idle it gets down to 18 to 20#'s. I for now can just rev it and kit doesn't go to 26#'s but I am not going to WOT and holding it there either.
Rite now I am installing a gauge pod on the A piller for vac and FP. The Vac. was easy but the FP is getting a little tricky.
I wish I would have done this from the get go. It was a bitch to adj the FPR while it was on the TBI.
Thanks for the encouragement now I just needc to get the tune rite.

 

The vacuum fitting on the BACK of your TBI should be for you MAP sensor ONLY. Run the brake booster and HVAC off of the fitting on the INTAKE. If you choose to run the VAFPR so be it, but I would still recommend a dedicated vacuum port. I have been told that a lot of new cars run the MAP and FPR off the same port, but I can't recommend if this is OK to share or not.

As for the vacuum port on your TBI that is on the front right hand (passenger) side, you should hook a vacuum gauge and see if you are getting engine vacuum @ idle. This can be tested by measuring engine vacuum @ the vac fitting on your intake so you have a measurment to compare to. If it has less vacuum or none at all @ idle, this is considered a "ported" vacuum and will not work for your FPR. From the looks of it you have a SB TBI, and the right fitting SHOULD be manifold vacuum as per the picture I posted.

 

Thanks. thats exactly how I have it now. The port on the front passenger side is getting full vaccuume so I am using it for the FPR. I should have it on the road tomorrow. I hope the tune goes smoother now.

 

It turned out real nice.

 

Now I have it on the road. It is running great I am doing VE learns now. One time there are not many corrections and the on the way home there are bunches. It seems to be running and idling much better. There is a problem though. Tried to do a burn out and it sounds like I don't know Pop corn not smooth and roasting the tires. I didn't notice fuel pressure to see if it is getting enough. I installed a vac. and fp gage on the a pillar. Should I just do some more learns or what?

 

Do you mean hesitating and misfire with "pop corn not smooth" ?

 

Yes it isn't just going.

 

Look at the datalog to determine if you are KC's and subsequent spark retard.

Or it coul be too much AE. That would be a gurgaling sound. Popcorn could be a misfire, ignition related...Just a guess.

 

Well that would be all good if I knew how to look at the data log. I don't know what a KC or the AE is. I will have to go back and read the How To section yet again. It doesn't say anything about a Data Log and how to look at them. Or at least that I can decipher. At this point I am ready to throw away the EBL and have a chip burnt. All I think I know how to do is a VE (don't know what that is or does)learn.

But for now I am battling the brakes. Putting a new booster in. Those 4 bolts are a bear.