I noticed I have a low fuel pressure problem. At idle with VAC line unplugged it was around 36psi. Where as it should be 44psi.

So I received my AFPR in the mail couple of days ago so I just installed it today. Thinking it might solve my problem as the original FPR might have been stuffed.

Well having put the AFPR in and everything back together with new Felpro gasket seals for the plenum. The fuel pressure seems still low!

The holley AFPR unit I have is adjustable from 30-65psi. I basically screwed the AFPR all the way down and still did not reach my desired FP. I managed to only get it to 42psi. But having it screwed all the way down it should be closer to 65psi according to the specs of the unit.

When I turn the key to on the Fuel pressure will hit 42psi and then I basically watch it bleed down to around 20psi within 1 minute without starting the car.

So somewhere along the line something is failing. I can pretty much rule out the Fuel Pressure Regulator.

What else could be the culprit?

The only thing I can think of is the fuel pump. How do I go about testing if the fuel pump is at fault?

I did however notice with the 6psi increase already the car is sounding much healthier and stronger.

I should add car sat for 2 years without being started just until 3 months ago. Had new paint done.

 

Have you changed the fuel filter?

 

the holley fpr bleeds preasure right away

they told me it was a saftey deal

pump is prob the prob

 

The fuel filter was changed about 4-5 years ago. I hardly drive the car. You think the filter could be blocked and not being able to give enough pressure?

Well that is good news that the holley bleeds pressure right away sounds like it is working fine.

Just can't get enough pressure with it. As it is maxed out and only getting 42psi.

I'll try and pull the filter and change it over and see if that does help.

So this means I can't crimp the feed and return lines to find the problem?? Since the holley bleeds pressure right away I will not find anything by doing this test?

 

I printed out the Service manual procedure to find the thing that is causing this problem. Will follow it on the weekend and see where I end up at.

I was just wondering though. Since I have an AFPR installed now at max pressure and it is only registering 42psi and on max it should be around 60psi. Does this rule out the pump at fault?

With my old stock fuel pressure regulator the pressure was around 35psi. So I have gained 7 PSI by adjusting the pressure regulator to max. But it really should be showing 60psi.

Does this tell me anything I am missing?

However though having it set-up like this the fuel pressure bleeds off so much faster then with stock regulator. The stock regulator held pressure even though it was only 35psi.

Couple of weeks back the pressure dipped down to 26psi but the next day it was around 30psi ( with vac line connected). But still way off the desired value, and I can really notice it in the performance of the car.

 

Sounds like your pump is dying to me. Tape the gauge to the windshield and observe the pressure while doing a couple of WOT blasts.

 

I have a digital gauge inside the cabin. Fuel pressure does go up when I go to WOT. It will raise by about 6 PSI and basically max out at the value when I have the vac line unplugged at idle.

 

It maintains the 42 psi @ WOT going through the gears????

If so, the pump is fine. If your just checking it with the vaccum line disconnected at idle, and not under load, there's no way to tell.

 

When I drive the car the fuel pressure will go up and hold. Will have to double check it to make 100% sure. But I am pretty sure that the fuel pressure will hold. It just seems I can't set the pressure to 44psi which is recommended.

The pump has never made any strange noises but I guess that does not mean it is not at fault. I guess I will find out on Sunday.

It will either be, Fuel Filter ( hope so), Fuel Pump, Injectors.

Nothing else it can be apart from those things. Unless a fuel line is buggered but highly doubtful.

BTW I am only getting 35-36 at WOT, Idle is around 29psi all with vac line connected.

 

Ive been down this road before lol and Ill tell you before you start thinking injectors or fuel pump..change that regulator diaphram right now.I laughed after getting a afpr and was only getting 30+psi.Installed my afpr and had that thing cranked right down and barely saw 40psi and then watched pressure instantly die off.I thought damn this afpr is crap..then i tore the plenum off again and said forgoet it im going to stick the original fpr back on for now.After doing that..god the car was worse..I was getting a whopping 15pis!!! and I could hear gas pissing out somewhere all over the intake.Sooo.. tear down again..looked more closely at the diaphram and then I spotted the tears in the rubber lining..Bingo.Ordered a new one..had it deleivered in an hr.Put it all back together with my afpr again..crossed my fingers and bam.. got my 45psi.Set it to 47 and wow car never felt better getting the fuel it needed.Lesson learned.After that i changed my filter and my fuel pump since they were the originalls 20yr old parts,got a lil better after that too but it wasnt my real problem.I spent half a day to find out I needed a cheap part and a 20 min job lol

 

This is a new AFPR, but I have ordered a new Stock standard regulator diaphragm and spring to replace it.

Well I followed the GM service manual procedure but I could not follow it 100% since it says to replace the filter right at the beginning.

But what I did do was pinch the fuel return line and then turn key to on. The pressure went to around 55PSI with the way I had the AFPR set.

But with car started the fuel pressure was around 28PSI.

So I will have to replace the fuel filter and see if it is blocking flow and hence effecting fuel pressure.

With the return line pinched fuel pressure held pretty steady at the 55PSI mark.

So to me this would rule out the pump right?

 

Well I changed the fuel filter and no change.

So looks like the fault is at the pump.

However I would like to test the flow of the pump first before I start replacing parts left right and center.

Any advice?

What I don't understand is can the fuel pressure regulator be compensating for not enough flow from the pump??? The AFPR unit is good for 60PSI and I am getting 42PSI out of on max setting.

Would this raise my fuel pressure even though the pump is not able to flow enough? This is what confuses me, still not 100% sure if the pump is at fault here.

In other words if my pump is giving me low flow rate, will setting the AFPR to 60PSI give me 42 PSI and thus compensate and give me almost the desired 44PSI pressure TPI wants?

 

Does your car surge while driving? Im about to do the same swap. My psi is 40 key on, 30 at idle and 38ish under a load driving. My car just started the surge and sat for a few years till the price of gas went up.

 

Oh man now that you mention it about the surging. When I 1st took the car from the painter and took it for a drive the 1st time, I did notice surging. Well what the car did was it started to decelerate and then accelerate when I held my foot steady. So yeah that sounds like surging. But last time I took the car out it did not show those symptoms nor has it showed it any time after that.

So what do you think, fuel pump?

 

i have the same issue after a bbk afpr install. im gonna install a new regulater shortly. not wanting to throw in a new fuel pump just yet. its just strange it only started it after the adjustable regulater installed

 

I too am waiting on a stock replacement regulator to try it 1st before I go any further.

 

Just like 86 White I'm thinkin to replace the diaphram in my car. Its a lot of work to change the pump. Isnt it odd that this summer so many cars seem to have a surge? My surge comes and goes but I notice it everytime I drive.

 

If the diaphragm in the Holley AFPR is torn, it will leak fuel out of the vacuum port of the AFPR when the engine is running. That's what happened to my Holley AFPR. Three times!

I finally replaced it with a Crane AFPR and have had no problems since.

 

Well I did some more fault finding today and something came up which might be of concern.

As far as I understand it fuel pressure at idle should be 36psi with vac line connected. Once you start driving fuel pressure will increase and once at WOT you should be at 44psi. That is what is optimal as far as I know.

Today with the fuel pressure bumped up via the AFPR the car runs a lot stronger. But keep in mind this regulator is a 60psi unit, but I am only able to get 42psi out of it when turned up to the max. So something is obviously wrong somewhere. I basically just have a band aid on it now with the AFPR.

The main thing that caught my eye today was when I was idling at a set of lights I tried turning on the lights and bam I lost 3-4psi with the lights on. From 32psi it dropped down to 28psi while the lights were on. Once I turned the lights off the fuel pressure went back to 32psi. It does fluctuate a little while idling and does not hold steady. It might drop 0.5-1psi and climb back up. If I applied the brake the pressure seemed to drop .5 and then return back up.

I checked out the fuel relay under the hood. And with the car running all voltages were above 13. With ignition on I basically had battery voltage across the terminals on the fuel pump relay.

So the last thing to do is to check out the connector at the tank under the car to make sure I am getting the same voltage there as on the relay. It might be a case of losing voltage along that wire?

What do you think?

 

I believe your on the right track. Yes, that would be a quick test.
Scoping the fuel pump current wave form would be a better diagnostic. I would suspect the pump before the wiring.
Don't forget that the ECM is also connected to the fuel pump circuit.

 

How would I go about scoping the current wave form?

 

did you ever findout your problem with your pressure? I am havin kind of the same problem.....i pulled my inline pump and put in a high flow 255lph pump and now my fans kick on all the time and my fuel pressure sucks.