Fuel Pressure q's

[Edwindo]

So based on some earlier questions I had, I went ahead and borrowed a fuel pressure gauge to check my pressures. Finally got time to start in on it, found the fitting on the rail, pulled the little cap off, hooked up the gauge and started testing.

Well, the gauge registered no pressure when I turned on the key. Tried several times, couldn't ever get it to register. Thought maybe the gauge I got was bad. Took it apart, made sure there wasn't a blockage. Then I realized I couldnt even get fuel to come out when I hit the little bypass button on the gauge.

So, I took the gauge off the rail fitting, and then with the key on and the pump pressurized, I used a screw and pushed the valve in. I got a tiny little drip of fuel, and then nothing. I could hold the valve in and no fuel came out. So, I am thinking that my pressure is so low that its actually not registering, but why isn't it at least putting out a stream when I open the valve?

The regulator and the check valve are all in the pump on an 03, correct? I'm thinking its way past time for a new pump. Oh well.

 

[Edwindo]

And one more thing: My expy runs. This is not a no-start issue.

 

[K5rnt]

What happened on my 99 was the pressure would bleed off when the truck was not running. I thought it was the check valve so I bought a fuel pump. When I dropped the tank I found that the rubber hose that connects the pump to the metal live was cracked and the clamps holding it on were loose. So that is where I was loosing my pressure. I went ahead and changed the pump since I already had it and had it out but I'm sure I could have gotten away with just replacing that hose and clamps.

 

[K5rnt]

Oh yeah. My symptoms were the truck would turn over for about 10 to 15 seconds before it would start. Now it busts right off every time.

 

[Edwindo]

Hmm, I'll have to take a look at the lines coming from the tank. Mine does start hard, but only cranks for 3-5 seconds if I go from cold. Been cycling the key to build the pressure so it doesn't have to crank so hard. I just don't understand why when the key is on there's nothing more than a tiny little dribble, and then it stops from the valve on the rail. Should have a constant stream, even if there's some loss, I would think. ?????

 

[K5rnt]

Did you check the pressure when it was running or just key on?

 

[Edwindo]

Just key on. Guess I could check it running too, huh? Just kinda got sidetracked by the initial findings

 

[K5rnt]

When you turn the key on the pump will only run a few seconds so it's hard to get a pressure reading that way. When you accelerate hard under load like a big hill does the engine clatter?

 

[Edwindo]

No, no clatter. And I just went out and started it with the key on while the gauge was on, and still no pressure. Maybe the little valve has some debris in it? I really don't think that could happen, not enough to block it completely anyway...

 

[Edwindo]

What else can I check? It's obviously getting fuel, because it starts, runs, and drives, WOT and everything. It does have a slightly rough idle, which is what started me on checking this, since poor fuel pressure can produce a rough idle.

 

[toms89]

Depending on the gauge it may need the schrader valve removed. If you had no fuel pressure she would not run.

 

[Edwindo]

When you say it may need the schrader valve removed, what do you mean? On the gauge itself or are you talking on the fuel rail?

 

[toms89]

When you say it may need the schrader valve removed, what do you mean? On the gauge itself or are you talking on the fuel rail?

The fuel rail.... Unless the gauge you are using is set up to fully depress schrader valve you will not get an accurate reading.

Any aftermarket fuel pressure gauges you would permanently install you remove the schrader valve.

Do not attempt this unless you can guarantee a good seal where the gauge screws on to the rail or you may have fuel spraying everywhere.

 

[Edwindo]

I've checked the fittings. The gauge I have is set up with the large threaded end on the hose, and then an adapter to go on the smaller (schrader) fitting. I have done several combinations of things, including screwing on just the small fitting onto the valve on the rail, and depressing the valve. A little trickle comes out, and I have checked the adapter in the gauge and it does seem to fit correctly and actuate the little pin in there.

It's still confusing to me that when I depress the pin in the valve on the fuel rail, I'm not getting a spray of fuel coming out of it with the system pressurized.

 

[toms89]

I've checked the fittings. The gauge I have is set up with the large threaded end on the hose, and then an adapter to go on the smaller (schrader) fitting. I have done several combinations of things, including screwing on just the small fitting onto the valve on the rail, and depressing the valve. A little trickle comes out, and I have checked the adapter in the gauge and it does seem to fit correctly and actuate the little pin in there.

It's still confusing to me that when I depress the pin in the valve on the fuel rail, I'm not getting a spray of fuel coming out of it with the system pressurized.

Depress schrader valve on fuel rail as she is running....it should come out under high pressure. If its not running as K5rnt said you may have no pressure if it bleeds down as the pump only runs 2-3 seconds on initial key on position.

 

[Edwindo]

Ok, will do. Thanks for all the help guys, I gotta run now and get kids to their stuff in a bit. Never a dull moment!

 

[K5rnt]

There are only so many parts in the fuel system. It basically has to be the pump, filter, regulator, or maybe an injector. I'm betting on filter or pump. Of course I have been wrong before lol

 

[Edwindo]

Ok, finally got my pump pressure tested. Turned out the adapter on the gauge that I was using didn't fit right, got that switched and hey presto, the gauge worked.

So, what we found was that the key on really didn't even register anything on the gauge, which is a little suspect, (just confirms that the pump check valve is bad) but once the engine was running, it showed 45 psi. When we hit the button to do the flow test, it only dropped about 1 pound, but we got air bubbles. Lots of very even, consistent bubbles in the output. My tank was 3/4 full, so somewhere its pulling air into the system.

Anyone have any thoughts on the situation? Is it just time for a new pump, or is there something on the return side that I should look for to find a leak?

Thanks again!

 

[K5rnt]

I say change the pump. I don't think there is anything on the return side that could cause you to loose pressure. The way I tested my check valve was I took the fuel filter off and blew on the line going back toward the pump. Since I could blow into it and hear bubbles in the tank it was pretty easy to figure out that was where my leak was.