New Injectors - Pressure Test

[Marccus]

I just installed new injectors and tested the fuel pressure before installing the intake manifold. Here's what I got:

Fuel pressure fell from:

max of 34 psi to 30 psi over 70 sec (3.4 psi/min)
30 psi to 28 psi in 1 minute (2 psi/min)
28 psi to 26 psi in 1.5 minutes (1.3 psi/min)

I'm using an "Actron CP7838 Professional Fuel Pressure Tester" with the Ford Adapter that is screwed onto the on Schrader valve finger tight. The hose on the gauge screws onto this adapter finger tight. Both have o-ring seals.

The rubber hose length on the tester is about 3 feet and there is a pressure release button the gauge which flushes fuel to a small clear plastic hose which can be directed to a towel or bottle.

I pressured the tester cycling the fuel pump eight to ten times and then flushed the fuel out. I did this about ten times to make sure all the air was out of the system and the max pressure was repeatable. When I press the pressure release button on the gauge, I can still see very small (pin head size) bubbles in the fuel.

I stated what the set-up was like because I am thinking that this rate of pressure loss may be acceptable with all the hose and finger tight o-ring connections versus a direct gauge connection with NPT fittings.

It's getting dark soon and I have to get the intake manifold on! Any comments?

 

[shoon]

Factory Specs for the fuel pressures are:

30 - 45 PSI engine running
37 - 43 PSI engine off

If your pressure is bleeding off a little bit thats normal... but if it drops off lots it might be a bad check valve in the fuel pump assembly.

 

[Marccus]

OK. Seems like I'm a little low on the pressure. I just installed a new fuel pump though about three months ago (Walbro).

It was suggested to me to check the check valve as it may be leaking backwards.

Is the check valve part of the fuel pump or on the pump discharge line?

Does the fuel pump itself have a relief valve that discharges back to the tank if there is a blockage upstream of the pump?

I installed a new pressure regulator two to three years ago and it doesn't seem to be leaking.

Thanks - have to do these things later since I have to get the intake manifoled back on now to at least get the car back on the road.

 

[shoon]

When you changed your fuel pump, did you come across one of these?


Its a pulse damper... used to weaken pressure pulsation created from the FP.

But.. because theres no way to clamp it onto the lines it usually leaks and could be causing your loss of pressure. Best way around that would be to get a piece of fuel hose and bypass it completely.

The check valve is built into the pump itself, its basically just a ball bearing that floats up and down. Because you already replaced the pump I doubt that is the issue.

 

[tompumped]

I removed mine when I did my pump not too long ago. Get the proper submersible fuel hose and the proper clamps if you plan on it.
If you can't find the hose I got it from napa.

 

[Marccus]

When you changed your fuel pump, did you come across one of these?

Yes, I did as I remember and I believed the new fuel pump came with it because I bought the fuel pump as a "kit" from a SHO recommended site that sells the Walbro pump as a kit and advertises that they test every pump. I can't remember the name of the site; I 'd have to dig it up.

 

[Marccus]

I removed mine when I did my pump not too long ago. Get the proper submersible fuel hose and the proper clamps if you plan on it.
If you can't find the hose I got it from napa.

OK. Thanks. I'll have to wait until the fuel tank gets to empty! (I carry around a small plastic fuel container of about 1 gallon). I have to get under the car and drop the tank. It's heavy for me to maneuver even with a little fuel in it. I have broken both shoulders crashing when cycling a while back and can't do a pushup anymore. I've been putting off the operations I need.

So the last time I had to wrestle with the lowering and raising the tank while on my back/stomach, I was hurting, cussing, and screaming .... for a week! The access door method under the back seat would be a better solution for me than dropping the fuel tank.

But I'll get to it.

 

[tompumped]

I think it's ridiculous to cut an access door unless you aren't physically up to the task. It's not very hard at all to drop the tank. Even in my other vehicle which is ten times harder to drop the tank I didn't make an access door.
I can get you the part number for the hose so you know you're getting the right hose.
If you don't want to wait disconnect the outlet on the filter and put a hose on it and energize one of the pins (can't remember which one) for the fuel pump on the same connector you use to pull the codes.
Hope you have a speedy recovery, must've been a nasty crash. I had a couple bad ones on dirtbikes.

 

[Marccus]

OK. Part number would be appreciated. I haven't had the chance to do this yet.

I was also wondering, has anyone installed one of those "expensive" aftermarket high flow fuel filters instead of remaining with the stock filter. Summit, Jegs, Earl's etc., make aluminum cylinder based cartridge filters which have a much higher flow capacity. Fram makes a HUGE filter for racing applications.

I change the fuel filter "periodically", but I can't help wonder if a paper element is the best to use for filtering, how often to change it and if it can be a restriction to flow.

Maybe they have something in the performance and upgrades section.