Fuel Presure droping off??

[mustangmarks]

Hey All,
I'll start with my set up: fuel system

190 FP
BBK Regulator
36LB injectors

Motor is a 306
With TF twisted wedge heads( no work done to them)
10:1 pistons
Performer RPM U/L intake
Paxton SN-92 (8lb)

So at idel I have 45lbs of fuel presure. If I slowly throttle it drops alittle but if I spike it the presure drops to 20 and studers bad. Is there something else I need? I'm open to any sugestions. I'm also taking the presure off the regulator. I tried 2 different gauges.

 

[webslinger67]

i hate to say it, but it sounds like your regulator is not getting the correct vacuum

 

[getusummm]

Without vaccuum, the pressure would remain the same, not drop. When is the last time you checked your fuel filter? The problem sounds like a volume issue. Dirty filters cant supply enough volume to maintain the pressure. There are other reasons also, but filters are the most common and easiest if everything was working fine before.

 

[mustangmarks]

i hate to say it, but it sounds like your regulator is not getting the correct vacuum

We are pulling vacum of the plastic fitting that is labaled AC. Is this correct? If not were should I be getting vacum from.

 

[HISSIN50]

I think Webslinger was indicating that without a strong vac signal to the FPR, there's no FP compensation for greater throttle application. Unfortunately for most cars, the pressure doesnt stay rock solid at 33 PSIG and only go up in a linear fashion, proportionate to diminishing manifold vacuum.

I'm not sure what else is on your vacuum circuit to the FPR, but try running it from a dedicated port (nothing else in a tee or branched from the direct manifold connection). This ensures a strong vac signal to the FPR.

Otherwise, post up if you can make this happen while stationary or if it's only under load. There could be a restriction issue on the way to the front of the car, etc.

Good luck.

 

[getusummm]

More Vaccuum=less pressure
Less Vaccuum=more pressure

If his pressure is dropping off, I really doubt its because he has too much vaccuum.

I would look into fuel delivery issues, especially a clogged fuel filter, or even clogged strainer on the pump.

Has this setup been working properly in the past? Could the pump be too small or going bad?

 

[HISSIN50]

More Vaccuum=less pressure
Less Vaccuum=more pressure

If his pressure is dropping off, I really doubt its because he has too much vaccuum.

I would look into fuel delivery issues, especially a clogged fuel filter, or even clogged strainer on the pump.

Has this setup been working properly in the past? Could the pump be too small or going bad?

I think we're saying the same thing. I was concerned with a lack of vacuum reaching the FPR, not too much vacuum.

Because he has a decent pressure differential (but we don't have baseline figures to deduce anything from), this was why I also thought a restriction or volumetric deficiency might be present.

 

[mustangmarks]

I had this similar setup in another car with a 190lph FP with stock heads and a B-cam with no issue. The only change I made was the heads and cam. On my intake I have a fitting in the front that is caped off I will try that. Do you think I need fuel rails that are bigger? Too go from 45 at idel to 18 at 4000RPM is pretty big

 

[mustangmarks]

I also changed the fuel filter and didn't make a difference

 

[mustangmarks]

Does anyone have a similar setup?

 

[bentley429]

To me it sounds like your FP is no good, my car used to do basicly the same thing it would go real low when I hammered on it but then it would skyrocket. I replaced my pump with a Holley FI 255 and so far it seems to work great.

 

[mustangmarks]

It drops low and dosn't come back til I let off the gas but if I slowly accelerate it stays around 40. Where in CT are you

 

[bentley429]

Northeastern part of the state