My 427 SOHC Build..... Finally the time has come!

[cobracammer]

As far as the fuel pressure regulator, i verified with Fast techs ( 3 different techs) and FAST recommends using ported vacuum and Not manifold vacuum

Ill check on the brakes tomorrow

[My427stang]

As far as the fuel pressure regulator, i verified with Fast techs ( 3 different techs) and FAST recommends using ported vacuum and Not manifold vacuum

Ill check on the brakes tomorrow

That sounds really, really odd.  So at idle, they want full fuel pressure, but when you crack the throttle lightly, they want LESS fuel pressure.

Of those regulators that use vacuum reference, I have never heard of that.  Additionally, it is very uncommon to even use it on anything but a blower or turbo car as we said earlier. 

I know I said this before, but even more so now, I think that line should be eliminated.    Not worth screwing with now, and certainly not critical, and won't cause any harm, but only adds complication for the ECM to overcome as you jockey the throttle

[cobracammer]

No hydroboost. It looks like a vacuum reference line on the brake booster. Ill link a hose from this to manifold vacuum and hopefully problem solved. Lol. Above is the clearest picture I could take

[My427stang]

Not to doubt those three techs 

But, here is a cut from their instructions, and honestly, I have never worked on an EFI system factory or aftermarket that used ported vacuum.  It just adds another component with a pressure change at the injector head that complicates tuning.

[My427stang]

No hydroboost. It looks like a vacuum reference line on the brake booster. Ill link a hose from this to manifold vacuum and hopefully problem solved. Lol. Above is the clearest picture I could take

Yep that line is the issue, it will fix it.  Best to use a dedicated line for that alone of you can, manifold vacuum, 3/8 line, maybe off the secondary TB if you can or of the manifold has a port directly.

That line does all the work for the power brakes, you'll be happy

[WConley]

What Ross said on the brakes!  You need a good diameter, dedicated thick-walled vacuum line all the way to a plenum in the intake manifold, preferably under a throttle body.  Under no circumstances should you tee off another line!  This is critical!

I'm not quite as clear on the fuel pressure regulator.  What I learned at Ford while working in the Fuel Metering Group, was that fuel pressure and manifold vacuum should have an inverse relationship.  At idle you generally want the lowest fuel pressure, and it should go up as you open the throttle.  Doing it any other way kind of defeats the purpose of having a regulator...  I also think you should be looking at direct manifold vacuum (but don't tee off that friggin' brake booster line!!  )

[My427stang]

One last post and off to bed, it will be good getting back to work in a week or so LOL

A vacuum referenced regulator is generally used to overcome pounds of pressure that an injector sees under boost.

In other words, when at 20 PSI of boost, to get the same amount of fuel out of the injector as zero lbs of boost there needs to be and extra 20 psi of fuel pressure, assuming no loss in the system. This is of course due to the pressure in the intake manifold that the fuel in the injector has to overcome.

Naturally aspirated fuel pressures are far less critical, but indeed the OEM engines use them anyway.  In this case they are accounting for inches of mercury in vacuum at idle, say 18, pulling fuel through the injector, then at full throttle, when vacuum is at zero the regulator has to increase pressure, but not a lot

In fact, the difference between 10-12 inches of mercury and zero at WOT on a naturally aspirated performance motor is a far cry from 10-12 inches of mercury at idle and 20 psi of boost at full throttle on a turbo or blower car.   So on naturally aspirated motors most guys just let the computer adjust pulse width to make up for it.  In fact going from 12 inches of vacuum to zero is a change of about 5 psi injector head pressure.  The change in a turbo car could be over 25 psi depending on how much boost

As you pointed out, in Jason's case, ported vacuum would increase fuel pressure at idle, then as he accelerated, it'd drop off and then later increase as the throttle position and load changed and ported vacuum came back up.  This makes a backwards and almost unrepeatable and unpredictable math problem for the ECM because it is looking for throttle position and vacuum from the engine but but the fuel pressure (which is unmeasured) is at times inversely changing compared to what it needs.  Actually, vacuum is even shutting off at some throttle positions due to the ported vacuum, which equates to what the regulator would see when at WOT (even though it's at idle)

If it was mine, I'd run it unreferenced, and I do on my own, and mine is an EEC-IV computer that previously used a vacuum referenced regulator. However, if any owner wants to vacuum reference on a naturally aspirated EFI system, it's fine, but it really must be manifold vacuum. It is a more repeatable function that better matches with the TPS and MAP inputs to the ECM.  On a turbo car, different story, I consider boost reference a requirement because it needs to overcome a wider range of head pressures

My 2 cents

[Nightmist66]

I'm not quite as clear on the fuel pressure regulator.  What I learned at Ford while working in the Fuel Metering Group, was that fuel pressure and manifold vacuum should have an inverse relationship.  At idle you generally want the lowest fuel pressure, and it should go up as you open the throttle.  Doing it any other way kind of defeats the purpose of having a regulator...  I also think you should be looking at direct manifold vacuum (but don't tee off that friggin' brake booster line!!  )

Exactly. On my old 88 t-bird SEFI 302, it had the regulator mounted on the fuel rail and a vacuum hose that allowed it  to pull on the diaphragm to bleed off excess pressure at idle(vacuum high) and increase the line pressure when vacuum dropped (rpm up). The bottom of the regulator had the return line hooked to it, so it could just loop back to the tank.

[cobracammer]

Hey guys. The only vacuum reference I can use is one of the porta on the throttle body. This means that off of the brake booster, there would be a larger diameter hose, but the i would use a plastic vacuum line reducer to go to a smaller diameter hose to connect to the throttle body vacuum reference port

Is this ok?

Also, i can swap the fuel pressure regulator over to manifold vacuum instead of ported. I just dont know why FAST would insist on using the ported one. lOl. Then again the techs have not been any help from there

[My427stang]

I am not sure what you mean, but you need the same size hose from brake booster to the engine.  You could probably go from 3/8 to 5/16, but you can't go down to the small 1/8 or 3/18 size.  Doesn't your throttle body have a big brass or steel tube coming off of it?

Also, FYI, the brake booster is not a "vacuum reference" that is vacuum actually doing work.

Generally the term reference means when some other equipment is using the vacuum source to change something, like the vacuum to a  MAP sensor or your fuel regulator, generally a small hose.

[My427stang]

See the port on the bottom of the throttle body?

That is where the brake booster line should go. 

[WConley]

Yup - Put your brake booster line on that big port, and don't tee anything else to it (or try to reduce it in any way).  Pull the fuel pressure regulator line off the other throttle body if possible, or at least from a place on the manifold far away from that booster vacuum port.

The reason is that a lot of air will flow back and forth in that big line when you're using the brakes.  (You have to suck out a lot of volume from that big canister.)  This will create funny vacuum levels in the line, so anything teed to it will get a bad signal.  Also it's bad safety practice to tee anything to a brake booster line, because any leak will suddenly and dramatically affect your braking power.

[WConley]

FYI - Ross, naturally aspirated engines do create meaningful pressures in the intake manifold, even compared to turbo applications.

1 inch of mercury = 0.484 psi, so if you're pulling 16 inches at idle, that is 7.74 psi of "negative boost" that the fuel pressure regulator compensates for.  I have found on the older EEC-IV EFI fords that fuel pressure varied from the low 30's to about 39 psi from idle to WOT. 

Many modern OEM fuel systems can do away with fuel pressure regulators on naturally aspirated cars, because the atmospheric "turbo" is always the same and you can factor out the pressure effects using software.

Here's a very good example of what atmospheric pressure can do.  They're sucking all of the air out of a railroad tank car:

https://www.youtube.com/watch?v=Zz95_VvTxZM

 

[cobracammer]

Hahaha. Hey Ross.  Yea after I posted, i found that exact picture. Just got back from the autoparts store actually. I actually still had the vacuum line on the saleen engine ( on a stand in the garage). It wasnt long enough to reconnect the Cammer Engine, so I went out and bought a new 4' length. The brake booster used 11/32" thick walled PCV hose, and i ran a fresh hose from the booster to the large port on the throttle body. That large port is actually only on the primary throttle body and its between the throttle bodies on the car. Im sure it wasnt needed, but I also put on hose clamps - 1 on each end.... To be sure I never loose my brakes. Lol

Also capped off the ported vacuum reference port and moved the fuel pressure regulator hose to the direct manifold vacuum port ( trust you guys more than FAST).

Other than an oil change, should be ready for a longer test drive.

[My427stang]

Bill, I think we said exactly the same thing, I am with you 100% and that's why I said 5 lbs in my example.  If he is pulling 12 in at idle, and zero at WOT, that's 12 * .484 or 5.8, if he is at 10 in at idle, it's a delta of under 5.

However, that's only about 10% change and usually there is enough injector duty cycle to make up for it.  However, a turbo car could have 20 psi, plus the same 5.8, which is effectively over 50 percent difference.  It is very unlikely injector duration could make up for that alone, not to mention the effects of spray pattern with a 25.8 psi delta.

That being said, I support vacuum reference completely and it allows for another tuning option, especially with pressure changes from elevation and/or weather.  I just find that on the tunes I build for EEC-IVs there is usually wiggle room to eliminate it.  Many others don't need it or use it as we both pointed out, especially if on the bottom edge of duty cycle, but using ported vacuum sure seems like a crazy idea.  My guess is the techs either misused the term, or said to pull it directly from the intake port, which added confusion.

BTW, neat link.  In USAF aircraft we pressurize less than commercial aircraft.  Almost every time I fly I open a bottle of water and close it up and put it back in my flight bag, when I land, it's always flat.  Not a train car or metal barrel, but shows the difference of FL350 vs being on the ground.  Even more incredible is to watch us in the chamber when we do a rapid decompression for training, uncovered water boils, plastic bottles and bags pop, not to mention the water vapor and air movement as it equalizes.  The first time I did it in the early 90s it was a little intimidating!