My truck has a mild rough idle. Recently it has started fairly regularly showing a lack of power on the low end. Every once in a while if you start it up from a cold start and pull out right away, you can floor the gas pedal and you will barely rev the engine (only in drive though) like its flooded. It actually stalled out on my wife twice last week w/ the truck at low speed and the AC on.

I've done a bunch of work to this truck in the few months I've had it. New parts and work done include:

-Lower Intake Manifold
-Cap/Rotor/Plugs/Wires
-TPS
-ICV
-PCV
-Fuel filter
-Water Pump
-Cooling system flush
-MAF Sensor clean
-EGR Cleaned
-I'm on the 3rd 500 mile oil change trying to get ahead of an oil sludge issue.

I've done a bunch of reading on the boards and went down to AutoZone to rent a fuel pressure gauge.

My readings are as follows:

62 psi while priming
58 after priming
50 after 10 minutes
53 psi at idle
62 psi when I crack the throttle
No noticeable drop in pressure from 10 psi after 10 minutes

Pressure seems a little low all the way around to me, but the leak down is what I'm thinking is the real issue.

I'm thinking a new spider is the answer here, but I want to run it by you guys before I drop $225 on a setup only to find I have a bad fuel pump. Any other ways to test this while I have the tester here still?

Any advice would be greatly appreciated.

Josh

 

Am I allowed to bump my own thread?

 

Regulated fuel pressure is OK but leak down shouldn't drop below 55psi after 10 minutes. These tests only tell you that leakdown is a bit much, it does NOT tell you where the leak is.

You'll need to modify the pressure tester so that fuel flow dead ends at the pressure tester. The easiest place to do it is at the fuel filter. Fuel pump running, pressure must be 73psi to 108psi and must remain above 55psi for at least 10 minutes. If it passes both of these tests, the leakdown is inside the plenum and need further diagnosis. If it fails one or both tests, the pump needs replacement.

 

+1, you can also look down the throttle body. If the passenger side is very clean or shows signs of washing then there is a good chance that the fuel pressure regulator is bad or the injectors are leaking. The best way to tell is with a visual inspection but that meens pulling the plenum.

 

Hey thanks guys. To dead end the fuel at the filter do I just unhook the fuel filter and attach the gauge to the line? Is there a special adapter available just for this application?

 

Did you read the fuel pressure test tech article? All of the questions you have asked are answered in that article.

 

I did, but I am a little confused as to the part w/ the T-shaped gauge. If I don't have the quick connect type of fuel lines, does that apply to me, or must I just find a way to adapt the gauge to the threaded fitting and dead end it? What is the point of the shutoff on the T-shaped gauge?

Sorry of you've answered this a bunch, but I wasn't able to find this info via search and I'm a little out of the realm of my standard brake changes and tune-ups on this one.

 

The tester at the bottom of this article is one that I fabricated a few years ago. It connects inline at the fuel filter. It will check regulated fuel pressure, maximum pump output pressure, and determine if the excessive leakdown is in the tank or in the plenum: https://blazerforum.com/forum/tech-a...agnosis-23038/

The fuel filter on your 2000 has a threaded fitting on the outlet end and a quick connect fitting from the fuel pump on the inlet. If you modify a fuel pressure tester to connect directly to the quick connect fitting, all fuel flow will end at the tester. You can test maximum pump output pressure and determine if the excessive leakdown is in the tank or in the plenum. It will not check regulated fuel pressure when connected in this fashion.

 

So the setup shown is so that you can hook up at the fuel filter and check it for max pressure AND regulated pressure, but if I just dead ended it at the filter I could still check for my regulated pressure at the schrader valve.

Sooo the T-shaped gauge is just to speed the process up when doing a fuel system diagnosis. Got it. Thanks so much.

I will check max pressure and bleed down today or tomorrow. If I find that all is well w/ the pump, and can safely say the issue is in the plenum, than the he most likely culprit will be a bad injector. If I were to swap out the spider and the regulator, would that be a pretty safe bet to handle any issues in the plenum, or is there anything else that could cause a bleed down in pressure?

 

The tool will also diagnose where the leakdown is by pressurizing the system, closing the valve, and watching for a drop in pressure. If you dead end at the filter, or use the shut off valve, you can not simultaneously check regulated pressure at the service port. The purpose of dead ending or shutting the valve, is to isolate the pump from the plenum. Both ways will shut off fuel flow to the service port.

Exactly, connect one tool and check three different things very quickly and easily.

That would be a reasonable assumption however, you can diagnose it even further and pinpoint the problem, but it would involve either an injector balance test, or remove each injector and visually check each spider line and injector for leaks.