Installed a new fuel pressure regulator today and got the car running again. However, my fuel pressure is reading 70psi?!

I removed the AFPR and reinstalled it. Still the same. I'm now checking for a clogged fuel return line.

I have removed the FPR, disconnected the flexible line from the plenum hard line and have tried blowing compressed air thru the plenum line and out the FPR return port. The air will not blow thru the line. The pressure is just building up and slipping past the tip of the air hose.

Shouldn't the air be able to blow straight thru?

 

The metal tube that exits the front of the regulator should blow straight through from where the metal line attaches at the front of the intake. You are doing this without the FPR attached correct? I don't think you can blow through it with the regulator attached to the lines.

The connection point near the intake where the metal line meets the metal tube rail assembly is on the left facing the engine. In other words, the return line tube is going to be on the left side closest to the pass. side when you're facing the engine.

Try disconnecting the lines where they attached up at the fuel rail assembly above the water pump. That'll rule out if it's just the 12" metal line that connects to the rubber line or the something in the rail assembly.

Hope this helps.

 

Yes, FPR removed and return fuel line disconnected next to power steering pump. Air will not blow thru the line and out the FPR port.

I also tried pressuerizing the fuel system with the FPr installed and the return line disconnected and no fuel came out the return line.

Either the replacement FPR I bought is bad, or there is a clog in the return line. I just want to verify which it is so I know how to proceed.

I don't want to pull the fuel rail unless I ahve too.

 

According to my service manual, you have a clogged line between the FP and where you disconnected the return line. You might want to get a couple pieces of rubber hose and clamp the air gun to the fuel line and blow away with the line disconnected.

 

Thanks Glenn. It was getting late last night and I don't think my neighbor appreciates my air compressor running at 10:30pm.

I'll try clamping a piece of rubber hose to the return line and to the tip of the air nozzle.

I also tried running some wire thru the line and it gets about 8" to 10" in and then stops. I may just have to pull the fuel rail and work on it off the car.

 

Okay, attached some hose to the fuel return line and to the air nozzle. Cinched the ends down tight with zip ties and set the air compressor at about 100psi delivery.

Still no air passing thru the line. It simply pressurizes and holds. I tried loosening the second fitting above the water pump and the air escaped.

I don't get it. How could it be clogged that bad? My Helm manual doesn't say much about clearing a clogged line. Is it possible there is a check valve inside the FPR base to prevent any backflow? Am I just spinning my wheels?

The only thing I can think to do at this moment is to pull the fuel rail, totally disassemble it and go from there.

 

Per the service manual Pressure above 47psi:

disconnect fuel return flexible hose. Attach 5/16 ID flex hose to pressure regulator side of the return line. Insert the other end end in a approved gas container. Note FP within 2 seconds after ingition "on".

Result:

Above 47psi
Check for restricted line from FPR to point where fuel line was disconnected. If line ok replace FPR

Under 47psi
Locate and correct restricted fuel return line to fuel tank.

Hope this helps.

 

Yep, read that in my Helm manual. I'm gonna take the fuel rail apart and check everything out.

 

Bret,

Let me see if I understand what you're doing. You are attaching the air nozzle to a rubber hose that's attached to the fuel return line above the powersteering pump. Correct? Everything on the fuel rail up top is connected including the FPR. Correct?

If so, I don't think you will get air flow through the return line with the fuel pressure regulator attached to the pipes on the rail. At least I can't on mine. lol!

Have you disconnected the tube coming directly out of the fuel pressure regulator in the front yet? The one that's beige sparkly colored and attaches to the FPR itself. It's the long tube on the rail assembly that exits the FPR and follows along the length of the left-side fuel rail and goes down to where the junction block fittings are at the front of the intake manifold.

Disconnect the tube from the front the regulator itself and then disconnect the pass-side junction fitting at the base above the water pump and then check for air flow.

I currently have mine disassembled to paint. If I spray hose water down the return tube on top where it attaches to the front of the FPR it comes out of the fitting where the two pipes connect together at that junction thingy on the bottom with the hex fittings on it.

I don't see how you could possibly have a blockage that can hold 100psi in that rail tube unless it has been smashed closed solid somewhere.

 

Okay, let me run thru this a little more clearly.

The Fuel Pressure Regualtor cover and spring/diaphragm have been removed. The steel return line runs from the FPR base, along the top of the fuel rail and stops above the water pump. At that point there is a fitting where a second steel line connects. The second steel line runs behind the power steering pump and stops. At this point there is another fitting that connects a short rubber line (the rubber line then connects to the steel line that runs to the fuel tank). Clear as mud, right?

This is the fitting I took apart and where I connected the air nozzle. I am trying to blow air back thru the steel return line. It should go right thru and exit out the base of the FPR. However, it is not. The line is simply holding the air pressure.

Either something is seriously blocked -OR- the FPR base has some type of check valve built into it to prevent back flow and I'm just wasting my time with the air compressor.

To remove the steel return line from the FPR base, the fuel rail assembly has to be taken apart. There is no way to do it otherwise.

My current plan is to disassemble the fuel rail and try to blow out the line with the FPR base removed. If that works, then the return line is fine and the problem could be in the FPR base.

All I do know for sure is that my fuel pressure was running at 70psi with the FPR adjuster screw backed all the way out. That means the excess fuel isn't exiting thru the return line and the fuel rail is running at what's known as "dead head" pressure. With just the return line disconnected, the fuel rail was holding 60psi.

To drive the car this way would be hard on the fuel injectors and could cause the engine to run rich. The factory GM Helm manual states just what Glenn posted. "Disconnect rubber return line, energize the fuel pump and check the pressure reading. If it's above 47psi, then either the FPR is bad or the return line is clogged."

There is no further instruction on how to clear a clogged line. The air compressor test was my idea.

 

Bret, I have an extra TPI unit that's off. Let me check it with the air before you start tearing the unit apart. I'm just finishing up changing the starter on the '91 and taking a break.

 

Have you checked the fuel return line from the rubber flex hose to the fuel tank? Just a thought!!!!!!!!!!!!!

 

Glenn, that would be awesome and greatly appreciated.

 

Bret,

I don't know if this will help, but I'll describe what I did to my FPR the other night. I tried it both on the original one and the new one I got from Addock (Delco parts place).

Using compressed air at about 80 PSI, I blew the air nozzle through the left and right ports on the side of the FPR. If I blow through one port, the air will come out the other port on the opposite side. So, it seems as though there is no restriction to the air going through the side ports on the FPR base.

However, if I try blowing air through the return port on the regulator, I get no flow whatsoever. The air seems to have no place to go and my nozzle lifts off the fitting due to the pressure.

I thought that maybe there needs to be vacuum applied to the regulator vacuum port. I applied up to 25"Hg of vacuum with my handheld pump. Still no flow though the return port on the regulator.

I'm thinking maybe you need both left and right feed lines going into the regulator at a certain pressure before the diaphram inside the regulator releases pressure to the return port. Both sides, not just one or the other. Just blowing air through the return port itself may not be the correct way to check it.

 

Thanks Mikos_89. The left and right ports will flow freely, that I know. The FPR is supposed to circulate fuel constantly around the fuel rail. To maintain a certain pressure, the FPR will return the excess fuel to the fuel tank thru the return line.

I had also posted on the TPI board and got a response from someone that you can't force air backward thru the FPR. So, I'll have to see if there is some other way to check for a clog.

I may try blowing air thru the FPR port and out the return line in the normal flow direction. If the line is clear, then it may be that the Auto Zone FPR diaphragm I bought is no good.

 

Update:
Tonight I tried forcing air from the FPR port out the fuel rail return line. The air pressure held – NO air flow.

So, I pulled the fuel rail, took it apart and found the problem. The return port on the FPR, as well about 1/4" of the return line, was blocked solid. It was kind of an off-white powdery substance, but it was packed pretty good. The rest of the return line looks clean. I also blew air thru it and the fuel rail just to be sure.

My air pressure test was the right thing to do. The return from the FPR is simply an open line, so blowing air backwards thru it is fine provided the FPR cover and diaphragm are removed.

Now I just need to pick up a new set of O-rings for the fuel and put it all back together. A new fuel filter will be going on as well.

 

Sounds like you had a corrosion problem. With the high fuel pressure, you would pumping more fuel thru your injectors and that can cause your car to run hot. You might want to run some injector cleaner cause some of that white stuff may have gone back in the system.

BTW, sorry for not getting back to you earlier. I went down to my brothers to get the extra unit and couldn't find it. It has to be some place between the two houses

 

Yeah, this may also cure why my car has been running hot under load. It's weird because the rest of the fuel rail looks clean. I had also recently been running Lucas fuel system cleaner thru the car every few fill-ups.

The tips of fuel injectors were pretty gunked up as well with gum/varnish. I cleaned them up with some throttle body/fuel injection cleaner.

Anyone know where I can get some new O-rings for the fuel rail? A couple looked a bit used up and since I have it apart I want to replace all of them.

 

The latest update:
Okay, I've got all the parts I need. It turns out that at dealer, the fuel rail O-rings do not come as a separate kit. They only come with a complete FPR assembly.

Well, after inspecting my FPR base last night, I noticed the return port was pitted and looked a little corroded. So, I had decided a whole new assembly is porbably what I needed. I hit my local Pontiac dealer, but they didn't have the assembly in stock. According to their computer system, neither did any other GM dealership. Good thing in a way, since they wanted $166 for it.

I then hit Kay Auto in Van Nuys. They had the assembly and it was only $87. I also picked up a set of injector O-rings and was out the door for $107. At the dealership, it would have cost $180+ total.

Once the new paint on my fuel rail has curred sufficiently, I can finally put the GTA back together.