Fuel pressure tested 65 psi at the fuel filter outlet, and leaked down to 55 psi after 10 minutes. Pressure tested about 40 psi at the test port. I replaced the fuel pressure regulator.

Pressure is now 42 psi at the test port, and leaked down to 38 psi after 10 minutes. I'm at a loss.

If I replace the fuel pump, will it raise regulated pressure to within spec? Is the replacement fuel pressure regulator faulty? Is there some other problem in the system? Please help, thanks.

 

We need the model year and if 96+ then older or upgraded spider?

George

 

It's a '98 Blazer with the old fuel spider.

 

You definitely still have a problem in the intake plenum. The system (at the schrader) should be able to hold the minimum output from the fuel pump as measured at the fuel filter output (55psi/10 min). Either the regulator is still bad or an injector(s) is(are) leaking or a line is leaking. There are a number of ways to go about narrowing this down the most sophisticated being a cylinder balance test (injector firing with a pulse box or high end scanner and monitor fuel pressure drop, compare cylinders). Let me know if you want help with this. The less fancy route is looking for clean spots in the plenum, smelling for gas in the intake, looking at the plugs, looking at fuel trims, pinching off a rubber section of the return line, the parts cannon.

In addition, this fuel pump does not really meet spec. The 55psi 10 min leak down is good but the initial charge is too low which says that this is either:

1. An inferior after market pump
2. An OEM pump on the way out
3. The net voltage to the pump is compromised
4. More than one of the above

The older spider is more sensitive to marginal fuel pressure so this needs to be fixed or problems will come.

What is the history on this fuel pump?


George

 

I don't know the history of the fuel pump. The vehicle has 270,000 km, and I bought the vehicle with 265,000 km. My guess would be it is an OEM pump on the way out.

I have a Vident iLink 400 scanner, but since the plenum is off right now I can't run the scanner until the engine is reassembled. I would prefer to fix the leak in the plenum before reassembly.

I'll run the pump again and see if I can smell gas. Other than the plenum, I suppose the most likely place for a leak is at the fuel pipe near the firewall. If so the leak should be visible.

 

A leak in the lines between the tank and intake is certainly possible but I have not seen this, only a restriction. Unfortunately, removing the injectors/poppets to see if they are leaking is often destructive testing because they can get damaged upon removal. The balance test avoids this but is more involved. If there is a rubber section in the return line, clamping that off would test the regulator.

George

 

I can definitely smell gas in the plenum after running the fuel pump. There is no sign of a leak at the fuel pipe. So it must be the regulator or the spider.

There might be a nylon section in the return line near the filter. Would clamping the nylon damage or kink the hose?

Maybe it's best to replace the spider especially since an upgrade to the newer style would be worthwhile. Thanks George, you are very helpful.

 

I would be careful with swapping out a nylon line because I could be tricky, depending on how it’s connected. And definitely don’t squeeze a line because you’ll deform it. If it’s leaking in the Plenum, there should be a clean area somewhere where the varnish is gone and you see bright metal, unless the leak is into a cylinder and it’s coming back through an intake valve, in which case it would be the injector/poppet. Replacing the spider and Regulator with high quality parts might be the answer but be careful because there’s a lot of aftermarket junk out there that can cause more problems than it solves.

George

 

The entire intake manifold is clean because I had it out to replace the gaskets. So it's not possible to see any shiny spots, I cleaned the manifold very well.

I'll plan to visit the autowrecker and get an OEM spider. If the wrecker doesn't have one, I'll buy a new spider from RockAuto, the Standard Motor Products FJ503.

 

I just went through this with another member, looking for a quality spider given that ac delco is no longer available. He settled on Echlin from Napa which I agreed looked like the best option

George