2001 5.3L fuel Rail Pressure Leak

I have a 2001 1/2 ton Silverado with a 5.3L and it began with somewhat hard starting. It took either a long crank or 2-3 cranks to start. I then noticed that after cranking a few seconds, then turning the key back to the "on" position, then cranking again - the engine would start right up - EVERY time.

I put a fuel pressure gauge on the fuel rail and after turning the key to the "on" position (without cranking the engine), the fuel pressure rises to about 45 pounds, then quicky drops down.

When doing same test on my neighbor's exact same truck - the pressure holds without dropping (all of this without cranking or starting engine). This is a "Return" type fuel injection system and all indications pointed to the fuel pressure regulator (a known problem with these engines). I replaced the regulator and problem remained.

Some points to add are that when you turn the key to the "on" position (again - not to the crank position), the (externally mounted) fuel pump runs for about 2-3 seconds, then shuts off. I assume this is supposed to happen - to build the fuel pressure to get ready to start the engine but the pump then shuts off until you actually crank the engine. The problem is that when the pump shuts off, my pressure immediately drops (but my neighbors truck holds the pressure).

I assume that if I had dirty/leaking injectors, it would run rough or misfire after starting, but this doesn't happen. It runs great.

It seems to me a leak somewhere either in the rail or the return system but where? There's no sign of leaks to the external world.

thanks for any ideas

If you had a leaking injector, you probably would notice it when running. You could always pull the plugs to see if one of them is wet from leaking fuel.

There is also a check ball in the pump on the return side. This could be the cause of your problem which requires replacing the fuel pump.

//2000CAYukon

> There is also a check ball in the pump on the return side.

Wouldn't the check ball/valve be on the supply side? And it's the regulator that holds the fuel pressure on the return side?

I was thinking that if it was leaking back on the supply side, I wouldn't have the hard starting problem that I currently do. Once I start cranking, the fuel pump would be always on and I would think it would start even if the check valve were leaking.

> There is also a check ball in the pump on the return side.

Wouldn't the check ball/valve be on the supply side? And it's the regulator that holds the fuel pressure on the return side?

I was thinking that if it was leaking back on the supply side, I wouldn't have the hard starting problem that I currently do. Once I start cranking, the fuel pump would be always on and I would think it would start even if the check valve were leaking.

You may be right on the check valve. The hard starting could be due to fuel leaking into the intake (i.e. flooding) or the fact that there is not enough fuel pressure when you go to start. There is a min fuel pressure needed to fire the injector.

If you pull the vacuum line off the fuel pressure regulator is there fuel in the line (maybe new regulator is bad)?

//2000CAYukon

The fuel pump check valve is at typically at the outlet. Immediate loss of fuel pressure after the pump stops is an indication of a check valve not seating. A slower loss of pressure usually indicated regulator or injector leakage.

I had the EXACT same problem with my 02 4.8. I replaced the FP regulator and fuel fiter and problem remained. I then determined that the fuel pump had a bad check valve, so I replaced my fuel pump which fixed the problem. The fuel system now holds pressure like it should, and the truck starts every time. I also considered the problem being due to a bad injector, but as previously mentioned, you would notice other symptoms.

rjeffrey wrote:

> then determined that the fuel pump had a bad check valve

How did you determine that the check valve was leaking? I thought about disconnecting and then capping the fuel filter outlet, run the pump a few seconds, uncap and see if I still have pressure.

Do you have an in-tank pump? There's an assembly on the front of my tank that I thought was the pump (it vibrates when the pump is running) but when I look up the part, I come up with in-tank pumps. And I saw a post from someone else with a 2001 that had to remove the bed to get to the pump (from the top of the tank).

2000CAYukon wrote:

> If you pull the vacuum line off the fuel pressure regulator is there fuel in the line (maybe new regulator is bad)?

No - and the old one didn't leak gas either. It sounds like that's the usual failure but I thought the leak could also be due to a stuck valve leaking back to the tank.


Blue Bowtie wrote:
> Immediate loss of fuel pressure after the pump stops is an indication of a check valve not seating.

What do you consider "immediate loss". The rail pressure drops from about 45 to 20 psi in less than 2 seconds - and then slowly down to 0. Sounds pretty immediate to me.

2000CAYukon wrote:

> If you pull the vacuum line off the fuel pressure regulator is there fuel in the line (maybe new regulator is bad)?

No - and the old one didn't leak gas either. It sounds like that's the usual failure but I thought the leak could also be due to a stuck valve leaking back to the tank.


Blue Bowtie wrote:
> Immediate loss of fuel pressure after the pump stops is an indication of a check valve not seating.

What do you consider "immediate loss". The rail pressure drops from about 45 to 20 psi in less than 2 seconds - and then slowly down to 0. Sounds pretty immediate to me.

You fuel pressure is to low.
Specs on it is 55/62 lbs of pressure
Here is some guide lines of fuel pressure checking.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 55-66 fuel pressure.
Cold start should be 55/62 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 55/62 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
If pressure does not come up with return line pinched or blocked off.
Go to fuel filter and hook a gauge direct to a line at fuel filter.
Pressure should come up to 75 or more and will hold after fuel pump is turned off.
If it leaks down there after fuel pump is turned off it is LEAKING BACK THREW PUMP CHECK VALVE OR PUMP MODULE LINES.
Post back your fuel pressure readings.
MT

The black box in front of the tank is the EVAP system. Your fuel pump is located inside your tank. I determined it was the pump by pressurizing the fuel system (turn the ignition on so that the pump cycles) then pinching off the return fuel line at the fuel rail. This isolates the injectors, if there is no leak-off, it indicates that your injectors are not the problem. Therefore, it must be the fuel pump (or a leak in the fuel line). I determined it was the check valve specifically from the information found on this website. Pick up a Haynes manual, the entire testing and replacement procedure is explained there. Let me know if you have any more questions

I had a similar problem on an 01 Silverado I recently purchased. My symptoms were that in starting the truck, I would have to hit the key one time to pressurize the system, then hit it again and it would start. I didn't have any fuel in the vacuum line, so I decided to replace the regulator anyways. Upon removal of the old one, I noticed that the "O" ring on the center of the pressure regulator was missing. I put the new one in with the "O" ring and now it fires right up.

I'm guessing you have both "O" rings in place (a small one in the center and large one on the outside) on the regulator, but I thought I would mention this as a possibility. Also, I have heard of people not getting the old "O" ring out, but I think it would be very difficult to put in the new one.

Good Luck!

ontheedge: Yes both O-rings are in place. I pulled the new reg to re-check and verify everything. And then...

I haven't found any easy way to check the pump feed pressure (connecting to the fuel filter or the fuel line just before the regulator) but it was easy to connect a gauge just downstream from the return line. I connected the gauge, turned the key on (pump runs for 2 seconds and shuts off). The pressure came up and held at 58 lbs (same as the rail pressure when engine is runnning).

My first thought was that the new pressure reg was bad, but then I connected a 2nd gauge to the rail test port and the pressure was 0. What was happening was the when the pump turned on, the pressure reg let some gas through (fuel pressure peaks above 90 lbs when pump turns on) and then the valve apparently closes as the rail pressure dropped (due to gas leaking back through the fuel pump check valve). The 6" or so of fuel line between the reg and the gauge held its pressure, but not the rest of the system.

My question is: do I really need to fix this? I will do it at some point either way, but it appears the only need for the pump check valve is to get that immediate startup when you turn the key. As it is now, I just pause for 2 seconds with the key in the "on" position, crank, and it starts right up.

Thanks for everyone's feedback.

I also delayed fixing this for a while, mainly because I didn't want to shell out $300 for a new pump. I would also leave the ignition on for a few seconds before starting, but even with doing that, if would still fail to start every now and then, or barely start and stumble untill enough fuel got to the engine. I figured that I should probably fix it, because if the check valve is bad, then the rest of the pump is on its last legs too, and I didn't want it to crap out and leave me stranded somewhere. That may just be my crazy logic, but that's why I replaced it.

ontheedge: Yes both O-rings are in place. I pulled the new reg to re-check and verify everything. And then...

I haven't found any easy way to check the pump feed pressure (connecting to the fuel filter or the fuel line just before the regulator) but it was easy to connect a gauge just downstream from the return line. I connected the gauge, turned the key on (pump runs for 2 seconds and shuts off). The pressure came up and held at 58 lbs (same as the rail pressure when engine is runnning).

My first thought was that the new pressure reg was bad, but then I connected a 2nd gauge to the rail test port and the pressure was 0. What was happening was the when the pump turned on, the pressure reg let some gas through (fuel pressure peaks above 90 lbs when pump turns on) and then the valve apparently closes as the rail pressure dropped (due to gas leaking back through the fuel pump check valve). The 6" or so of fuel line between the reg and the gauge held its pressure, but not the rest of the system.

My question is: do I really need to fix this? I will do it at some point either way, but it appears the only need for the pump check valve is to get that immediate startup when you turn the key. As it is now, I just pause for 2 seconds with the key in the "on" position, crank, and it starts right up.

Thanks for everyone's feedback.

There should be a schrader valve on the fuel rail for pressure testing.
If the fuel pressure is that bad it need fixed now not later.
Run the that I posted and it will point you to the problem.
Post back the pressure readings.