f/p regulator Q & A

[1 RARE T]

Could someone please explain how the f/p reg. works.

There is vacuum until boost and then does the boost goes threw the line from the t/body / block to put pressure on the diaphram to increase the f/p?

I'm trying to figure out why my f/p only goes up 20 psi when it should go up 25 psi for the boost I'm running (with alky).

Already changed the fuel pump and filter but that was'nt the problem. Pump was getting old and filter had been in there for 4 years. Only drive the car 5k a year.

 

[QUIP'6']

what is your fp with line off if its 42# where most chips call for then it should goto 67# at wot if not fuel pump is not keeping up volume wise also check your volts at wot if below 13 then you need to check why because that would cause low f. pressure.

 

[CTX-SLPR]

How high can a regulator go? The program I'm planning on using calls for a static 52lb, however I can change that if need be. Combine that with 24psi and I'll need 76psi of pressure, will it be up to that?

Thanks,

 

[1 RARE T]

what is your fp with line off if its 42# where most chips call for then it should goto 67# at wot if not fuel pump is not keeping up volume wise also check your volts at wot if below 13 then you need to check why because that would cause low f. pressure.

My f/p line off is 45, so it should be 70. It only gets to 62.Alky is saving me at the moment.

Pump is new and hot wired. 14v + at idle.

 

[QUIP'6']

My f/p line off is 45, so it should be 70. It only gets to 62.Alky is saving me at the moment.

Pump is new and hot wired. 14v + at idle.

my pump was 4 months old and it went south

 

[1 RARE T]

Thing is......I changed the pump literally yesterday because I thought it was tired.

Turns out there was nothing wrong with my old pump. Does exactly the same thing.

 

[1 RARE T]

I'm still pulling my hair out with this.

Car has a really weird studdering noise under full boost which is 24 psi spraying alky. No k/r at all and pulls just like it always has.

So far I have changed,

Fuel pump
Fuel filter
Regulator
Plugs (42's gapped at .32)
Coil pack
Vacuum block gasket

The plugs I took out had a grey look to them but only on the pass. side. Drivers side looked nice and brown.

Noise is there as soon as boost goes past 20 and almost sounds like valve float. Don't think it is because the R.P.M. is low when it starts and continues all the way through.

 

[strikeeagle]

Have you changed the ignition module?

strike

 

[BlownZ]

What pump did you use?

 

[BlownZ]

What kind of injectors are you using? I know some of the Blue Top SVO injectors would actually lock up under too much pressure...although I think it is around 80 to 100 psi before that happens.

 

[1 RARE T]

Have'nt done the module yet. That was the next thing.

Pump is the new replacement for the 340M.

The Blue Tops should go anyways. I'm just about at the limit with them.

 

[Jerryl]

.... There is vacuum until boost and then does the boost goes threw the line from the t/body / block to put pressure on the diaphram to increase the f/p? ....

Yes.
You have have a leak in your "boost sensing line" or at the FP under boost (??)

 

[Ormand]

Most fuel pressure regulators won't have an "upper limit", at least not one that will mess things up. They see vacuum/pressure under the diaphragm, from the fuel, and on top of the diaphragm, from the sensing line going to the dog house or throttle body. Then they try to maintain the difference at whatever the "line off" setting is. So the spring in the FPR only has to deal with whatever that setting is. Some of them may not enough spring travel to get to 50 or 60 psi "line off", but with 45 psi, they will happily handle 70 or 80 psi fuel pressure.

 

[1 RARE T]

So, just to clarify. Considering I'm running 24 psi. boost.

Line off setting is 45. Line on pressure is 38.

Should f/p go to 69? (45 + 24 = 69).

Or should f/p go to 62? (38 + 24 = 62).

62 is what I got.

 

[Squid4life]

"""Or should f/p go to 62? (38 + 24 = 62).

62 is what I got""

This is correct. You should go up 1 PSI fuel per 1 PSI boost from the "line off" reading. Because you are not "really" at 43 for sake of reading reading under boost, you are reading at 38, so increasing from 38. Right?

 

[1 RARE T]

Huh???????

Line off is 45psi.

Line on 38psi.

 

[Mike Licht]

It should go up from the line off reading. the pressure only goes down at idle due to vacuum lifting the diaphram in the regulator.

A quick regulator tutorial:

The FPR is in the return line, inside the reg there is a diaphram with a metal center that cover up the return path to the tank. when vacuum is applied the diapham is lifter and more fuel can be returned so pressure goes down, when boost is applied it presses down on the diaphram and less fuel can be returned to the tank so pressure goes up. It is a very simple device.

Mike

 

[Squid4life]

"""Or should f/p go to 62? (38 + 24 = 62).

62 is what I got""

This is correct. You should go up 1 PSI fuel per 1 PSI boost from the "line ON" reading. Because you are not "really" at 43 for sake of reading reading under boost, you are reading at 38, so increasing from 38. Right?

Actually what I meant to say was from the LINE ON... But Mr. Licht has brought it up differently. Now I am confused. You set it at 43 line off. Line on it drops to 38. Now when you get into 24 lbs of boost the gauge should read 62, correct?

 

[Blazer406]

Actually what I meant to say was from the LINE ON... But Mr. Licht has brought it up differently. Now I am confused. You set it at 43 line off. Line on it drops to 38. Now when you get into 24 lbs of boost the gauge should read 62, correct?

No..... you have gotten confused....

Line off is 0 psi..... which is 43.....
Line on...idling.... is actually sucking on the diaphram....instead of pressurizing the diaphram (which adds 1 lb FP to 1 lb boost) .. the vacuum has the opposite effect of boost on the fuel pressure... so when you plug the line up.... it lowers the FP...... again... this is vacuum which is not the same as 0 psi boost..... soooooooo .... if you were going to 24 psi boost...... you would need (as compared to 0 boost) 24 additional psi in fuel pressure just to keep up.....

so 43 (line off) +24 = 67 psi fuel pressure .......

HTH

 

[bison]

What kind of injectors are you using? I know some of the Blue Top SVO injectors would actually lock up under too much pressure...although I think it is around 80 to 100 psi before that happens.

From my experience the pintle style injectors (like stockers) are less prone to mis fire under high pressure. The rotary disc ones seem to get lazy around 80psi especally without a volt booster. Most of the single pump setups coupled with stock sender and fuel lines will have a hard time with over 75psi and 42lb injectors. If you plan on running 25-30psi with heads and turbo then you will be needing dual intake pumps unless you have meth injection. One leanout at that level will cause some serious damage . Going over 120mph in the quarter at 3600lbs with one intake pump and the stock lines is risky. Not worth it imo.