OK, it's been a few weaks, but I'm back at it! I got the new spider in with new nut kit, but when I checked the fuel presure, key on, the presure goes to 62 lbs drops to 55 lbs, but then it slowly continues to drop presure! I haven't put the plenum back on yet, so I can see the spider and lines. There are no apparent leaks anywhere, so why is the presure droping? Can there be a presure leak anywhere without gas leaking? Could the presure gauge itself be leaking presure without leaking gas? I did notice that when the pump is on, you can see some air bubbles moving in the return line. Is this a sign of something? Also, what is the perpose of the return line?

 

In post #1, pump running pressure was 80 psi, which is fine. 10 minute leakdown was 65psi, which is also fine. Those two readings tell us the pump is fine, (good pressure, and acceptable leakdown).


Provided there are no leaks in the pressure line, (3/8") between the fuel filter and the plenum, any leakdown below 65psi, is inside the plenum, (leakdown to 50psi is acceptable). This includes the nut kit pressure line connection to the injector, the all of the poppet valves & spider lines, the injector, and the fuel pressure regulator. If there is a leak in any of those, except the poppets, you would see it while the pump is running. If the regulator is leaking internally, you would not see it. The outlet of the regulator is connected to the return line, which directs the unused fuel back to the tank. A leak in the return line would not cause excessive leakdown, and would not show up on a leakdown test. If the diaphragm in the regulator is leaking, it would cause excessive leakdown, but you would not necessarily see it.


You mentioned that you could see bubbles in the return line.... I assume you see them in the nut kit return line, is that correct? If so, you should NOT see bubbles after the pump shuts off. If you do, I would suspect the regulator diaphragm is leaking and causing your excessive leakdown. There is a way to test the regulator for leakage, but it's rather tricky and will destroy the regulator, if not done correctly.

 

Thats right, I see the bubbles in the nut kit return line. They flow one way when the pump is on, and the other way just after the pump shuts off. I don't remember which way is which. Is it common to get a new spider, and the regulator leak? It was a rebuilt from Napa auto parts. You also mentioned the poppets, if they were leaking would fuel be comming out, or could they just leak air? To summarize, the only thing that would leak out presure, ( including the presure gauge) and not show signs of gas leaking out, is the regulator?

 

Hey Captain, are you out here? I'm getting ready to work on my car, and was hoping you had some more insight on my fuel presure problem! Thanks again for all the help!!

 

While the pump is running, engine running or not, fuel is constantly being sent back to the tank through the return line. With the engine off, and the pump running, return line pressure equals fuel pump max output pressure minus regulated pressure, roughly 20psi on yours, (less than that when the engine is running). When the pump shuts off, return line pressure immediately drops to zero, and the fuel just drains back to the tank. It may take a few seconds or so for the fuel to drain, and during that time you'll see it bubbling in the line.


With the poppet nozzles removed from the lower intake, and the fuel pump activated, there should be zero fuel dripping, oozing, or spraying from the poppet nozzles. When the pump is activated, it pressurizes the system, (right up to the poppet nozzles) and any air is immediately bled into the return line. Air pockets in any of the spider lines would quickly be bled during cranking, but if leakdown is within spec, there won't be any air. Low pump maximum output pressure, and excessive leakdown, are what cause long cranking times to start the engine.


If the diaphragm inside the regulator leaks, you would see fuel exiting the tube on the rear of the regulator while the pump is activated. If the valve plate inside the regulator is leaking, you wouldn't see any external leaks. Both will cause excessive leakdown.

 

What tube are you refering to on the rear of the regulator ( is it the return line?) If the valve plate is leaking, is it leaking air, or where is the fuel going? Does the fact that the air bubbles go one direction when the pump is on, and the other direction when the pump shuts off mean anything?

 

A couple of paragraphs down from the top, it explains the fuel pressure regulator: https://blazerforum.com/forum/2nd-ge...eakdown-88305/


The metal tube is part of the regulator and it's exposed to manifold vacuum, so it does not need a vacuum line.


There is a check valve in the outlet of the fuel pump. The valve plate is the check valve at the other end of the fuel system. The valve plate seals in pressurized fuel. When it regulates pressure, it opens and allows the excess pressure and fuel back to the tank. If the seal leaks, fuel leaks past the valve causing excessive leakdown. The fuel goes back to the tank through the return fuel line.


"Does the fact that the air bubbles go one direction when the pump is on, and the other direction when the pump shuts off mean anything?"

Yes, when the pump shuts off, it means the fuel is draining back to the tank, and it should stop bubbling within a few seconds, (after the return line empties). If the valve plate is leaking, it will continue to bubble until fuel pressure drops to zero, or the valve plate seals.

 

I ordered a new spider, should get here in a few days. Lets hope that was the problem!

Would it hurt to cap off the nut kit fuel line at the point where it enters the spider, in order to check for leaks, and the fuel presure from there back to the pump? Can the nut kit line handle the 80 lbs of presure? If I could check it from there, it would comfirm that the pump is holding presure, and there are no leaks in the lines from there back including at the fuel filter.

 

You've already checked the pump pressure and leakdown at the filter, and it's fine. You also checked pressure and leakdown at the service port, and found out regulated pressure is 60psi, (OK) but leakdown is excessive. These results mean there is something leaking in the plenum, we've known that since post #1.

 

OK, installed the new spider, and it's holding presure! Pump running 61 lbs, pump off 55 lbs, right at 50 lbs at 10 min. 46 lbs at 20 min. I think this is good, and shows that the original new spider I got was bad! One thing left to do, put everything back together. While I have everything off, I'm going to to change the Cap, Rotor, Plugs and Wires! Do I apply Dielectric grease to just the boots, or to the metal connectors also? If so, do I apply it generously or sparingly to the metal connectors and post inside the Cap?