Checked my FSM and it says "Ignition on, fuel pump will run for about 2 seconds. Note fuel pressure with pump running, should be 34-39 PSI and hold steady"

I only have 35 psi when the pump is running, engine off, only 30 PSI during driving around. Shouldn't my driving PSI be between 34-39 especially at WOT? 30 seems too low. I know the pump isn't bad because when I block off the return line my pressure goes up to 60 PSI. It has to be the regulator.

 

How do you monitor fuel pressure while you are driving?

 

It sounds like your regulator is working fine. Those numbers are typical for a stock 85. Quit worrying about what people "recommend".

You said this problem started when you installed the SR plenum. Did you install the SR manifold too? Have you verified all the injector connectors are installed correctly? I know a couple of them are hard to get at with the SR. My intuition tells me the problem is related to the work you did.

 

I think that the work I performed is related to my problem too.

I installed a TPIS bigmouth base, super ram runners, and super ram plenum, and a Holley AFPR.

All of the injector connections are on tight.

I monitor pressure while driving by taping my fuel pressure gauge to the windshield. It is pure genius.

I tore down the intake (again) to see if my injectors were leaking. I primed the fuel rail with the injectors in the rail but out of the manifold to see if I could see any of them leaking and I couldn't, and my fuel pressure still dropped at a rapid rate.

Is it possible for fuel to make its way into the plenum if the FPR isn't leaking? My plenum had gas in it.

 

I have not had fuel in the plenum but it does get a coat of oil. I have been told that is normal. Does the vacuum hose to the AFPR have fuel in it? If so, there's a problem. If not, the fuel is coming up the runners.

You also said BLMs were all over the place. Were the numbers showing rich or lean? How are they at idle vs. driving?

 

BLM's are low at idle & lower rpms, but when i took it up above 3000 rpms the BLM's were in the 150 range. Below 2000 RPM and it was at 108.

I applied ten inches of vacuum to the regulator and a small amount of gas came out into the hose, but the more I pumped the vacuum pump no more fuel came out. Is the regulator supposed to hold pressure? Mine doesn't.

 

A quick drop in fuel pressure can be caused by something at the engine end, the gas tank end or anywhere in between.

There's a procedure of clamping off the return line (I used pliars) to isolate whether it's in the tank/pump or up front. That's how I located one on the 86 I use to have.

If you clamp the return hose and the pressure holds then it has to be rearward of the engine. If it still drops it's up front. Clamping the return line prevents any fuel from returning to the tank so if the leak is at the tank (or one of the lines leading to the tank) the fuel is being prevented from getting there and dropping the pressure.

You can also clamp the supply line and if the pressure quickly drops then you'll have further proof it's at the rear. The pump builds pressure in the supply line that you then clamp off. But as soon as the pump shuts down, the pressure drops telling you something rearward is allowing/causing that to happen. Probably at the pump unless you're seeing gas puddles on the ground.

Once you know which end of the car to look at it becomes easier to go through the limited number of things that could be the cause. The regulator is a definite suspect.

Mine turned out to be a connection at the pump that I replaced with a new piece of rubber hose.

Hope this helps.

Jake

 

Pretty sure its the regulator now.

Just got in from working on the car.

I clamped the return line, I have the injectors still connected to the rail but not in the intake so I could see if they were leaking. None of them leak. All ohm out at 16.2-16.5 cold.

When I primed the rail the pressure shot up to 80 PSI (why higher than last time?) and I watched gas squirt out of the regulator vacuum port.

What I don't understand is how is this regulator bad? The diaphragm looks 100 times better than the old crappy one. This is the Holley AFPR part number 512-501 as shown in the link below.

http://www.jegs.com/i/Holley/510/512...0002/-1?CT=999


Should I give replacing it a try or is there something I can do to R&R it? Could I put a plug in the vacuum port and just have the car run at whatever PSI I set the regulator to?

 

I am in the process of doing the same thing on my L98. I got the regulator from Corvette Central. I am pizzed because it came without any directions and no diaphragm. Looks like I have to go to NAPA in the morning and hope they can find one for me.
Fortunately for me I kept an old copy of an August 2007 Corvette Fever article that tells how to do the install. The very last paragraph says the recommended spec is 40.5 to 47 psi with key on, pump running, and the vacuum line disconnected.
Good luck and for heaven's sake be careful and don't burn the car or the garage down!

 

It doesn't seem to add up to disconnect the vacuum line if the engine is off as there wouldn't be any vacuum anyway!

 

They mean with the engine running. And yes 40-47 is recommended when installing an adjustable reg.

Sounds to me like there is a problem with the diaphragm. Remove it and make sure there's no tears or pinholes.

 

I took the regulator apart again, and I looked at the diaphragm and it looks fine! I looked at both sides of it very closely and I can't find any problems with it.

Could it be that I am somehow installing it wrong? I made sure the diaphragm is "face-up" so that the side with the retainer for the spring is facing the spring. install cap, and then install screws.

Is there a certain order for the screws to be installed?

 

I find it odd that both known good regulators are bad. The Holly unit I sold you with the intake worked fine on my car. And your stock unit that worked okay.

Thought, gas in the plenum going in the regulators. How can gas get in the plenum, evap system? You have a huge pressure leak somewhere.

 

If you recall I wrote on this before. Fuel pressure operates differently than many people think.

The LOWER the vacuum reading the HIGHER the fuel pressure.

So, with the vacuum hose DISCONNECTED and the vacuum source plugged, there is NO VACUUM to the regulator so the pressure will be at it's HIGHEST.

Back to the vacuum hose CONNECTED: Since the regulator now sees vacuum, the pressure will be LOWER.

When at WOT vacuum drops off to near ZERO so the pressure is HIGHER.

Correct pressure is checked with the vacuum hose DISCONNECTED and the vacuum source plugged. Under those conditions GM's recommended pressure specs should be seen on your fuel pressure gage.

I posted those numbers in a previous post; just track 'em down.

Remember, too, that the GM recommended fuel pressure ranges are DIFFERENT for certain year engines. You have to be sure you're looking at the recommended pressure range for YOUR engine.

Jake

 

I am not to the point of determining which fuel pressure range is correct for my engine because both of my regulators are leaking!

I have no idea why, I ordered another Holley unit, if that one leaks then I am installing them wrong or god hates me.

 

Well, if you've tried assembling it the way you feel is correct and it leaks - or both of them leak, my next step would be to assemble it the OTHER way and see if THAT works.\

There's got to be a diagram on-line that shows an exploded view of how the regulator should be assembled. I suggest trying to track down one; will remove all the guess-work.

Jake

 

http://www.holley.com/data/Products/...99R10036-1.pdf

Here is the diagram of my regulator. I will try assembling it the reverse way and see what happens..

Assembled it in reverse and no beans. Still leaks.. this is getting very frustrating!

 

Here's what I saw in the diagram: The diaphragm ends are of two different sizes. Are you sure you installed it with the BIGGEST END UP?

Is there any kind of recessed groove that the diaphragm has to fit into for sealing purposes?

Is it the original diaphragm? Right size, etc?

From personal experience, on a couple of occasions I've removed the fuel rails with the injectors still attached and pressurized the fuel system repeatedly to check for any injector leak. In no case did the regulator leak or spray gas like yours have.

Sure hope you can track down the cause.

Jake

 

Any chance there's a nick or burr in the base? Anything that would allow gas under pressure to squeeze through.

Jake

 

I was just responding to the original question you posted when you opened this thread. Would you rather I not have bothered? LOL

Jake