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BruceK

By BruceK
in Ask A GM Technician

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Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
41 minutes ago, BruceK said:

I changed the filter 18,000 miles ago. It should be okay I only purchase gas from one source and no problems with other vehicles. One of the suggestions was to replace the fuel pressure regulator as it was only a few dollars. According to my research this valve is almost eighty dollars. Do you think this is a wise move?

If you put a pressure gauge on the Schrader valve and with the engine idling, disconnect the vacuum line, you should see a change. If you don't see a change that should mean the regulator is defective.  It's been a few years since I have been "on the bench" but I think you should be testing with a good pump or a lot higher pressure than you are seeing. 

If you have rubber flex line between the pressure regulator and the steel line on the chassis as opposed to a plastic line, take two wrenches and a pair of vice grips and put one wrench on each side of rubber line and use the vice grips to clamp off the fuel line.  It's kind of awkward but if you don't have a pair of the wide jaw clamp pliers two wrenches and vice grips work.  Don't try this on plastic lines.

 

Clamped off return line should put you over 60psi.  If it doesn't you have either a bad filter or pump.  When you replaced the filter, were you having issues, or was it just replaced as part of normal maintenance? 

 

There are only three components that can impact fuel pressure. The regulator, the pump and the filter.  The pump tends to get noisy when it starts to fail. 

 

If the regulator passes testing, that only leaves the pump and filter.  Since you would replace the filter if you put a new pump in, replace the filter first and see what happens.  If there is no change you now know its the pump.  If the filter fixes it, the pump won't be long before failing from the extreme strain a plugged filter puts on the pump.  Sometimes logic sucks. 

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
Just now, riverbanks said:

Where is that rubber flex line?

From the regulator to the chassis. Rubber means like a braided covered line about a half inch or larger outside diameter. It's what allows the fuel line to flex with engine vibrations. 

BruceK Enthusiast

BruceK

Posted
  • Author
Posted
21 hours ago, Doug_Scott said:

If you put a pressure gauge on the Schrader valve and with the engine idling, disconnect the vacuum line, you should see a change. If you don't see a change that should mean the regulator is defective.  It's been a few years since I have been "on the bench" but I think you should be testing with a good pump or a lot higher pressure than you are seeing. 

If you have rubber flex line between the pressure regulator and the steel line on the chassis as opposed to a plastic line, take two wrenches and a pair of vice grips and put one wrench on each side of rubber line and use the vice grips to clamp off the fuel line.  It's kind of awkward but if you don't have a pair of the wide jaw clamp pliers two wrenches and vice grips work.  Don't try this on plastic lines.

 

Clamped off return line should put you over 60psi.  If it doesn't you have either a bad filter or pump.  When you replaced the filter, were you having issues, or was it just replaced as part of normal maintenance? 

 

There are only three components that can impact fuel pressure. The regulator, the pump and the filter.  The pump tends to get noisy when it starts to fail. 

 

If the regulator passes testing, that only leaves the pump and filter.  Since you would replace the filter if you put a new pump in, replace the filter first and see what happens.  If there is no change you now know its the pump.  If the filter fixes it, the pump won't be long before failing from the extreme strain a plugged filter puts on the pump.  Sometimes logic sucks. 

Doug,

 

Started the engine and disconnected the vacuum line to the fuel pressure regulator. There was no change in the pressure. Does this mean the fuel pressure regulator is defective?

 

I do not believe that the fuel pressure regulator is defective, based on the following: When I checked the pressure the very first time it was running 30-32 psi at idle. I shut down the engine. At shutdown the pressure was 30 psi. After ten minutes, the pressure rose to 40 psi. I attributed this to the hot engine heating the fuel in the lines causing a pressure increase. If the pressure regulator can hold 40 psi this indicates to me that it is not the source of problem. I have been so humbled by this issue, I thought I was a pretty good diagnostician/technician but these newer systems can be daunting.

 

When I replaced the fuel filter it was done as part of my preventative maintenance program. I changed the fuel filter again and there was no change in the pressure.

 

I can barely hear the pump run. How can I force the pump to continue to run when the engine is not running? Is this a wise thing to do? Wanted to dead head the pump.

 

 

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
On 7/5/2019 at 4:39 PM, BruceK said:

Doug,

 

Started the engine and disconnected the vacuum line to the fuel pressure regulator. There was no change in the pressure. Does this mean the fuel pressure regulator is defective?

 

I do not believe that the fuel pressure regulator is defective, based on the following: When I checked the pressure the very first time it was running 30-32 psi at idle. I shut down the engine. At shutdown the pressure was 30 psi. After ten minutes, the pressure rose to 40 psi. I attributed this to the hot engine heating the fuel in the lines causing a pressure increase. If the pressure regulator can hold 40 psi this indicates to me that it is not the source of problem. I have been so humbled by this issue, I thought I was a pretty good diagnostician/technician but these newer systems can be daunting.

 

When I replaced the fuel filter it was done as part of my preventative maintenance program. I changed the fuel filter again and there was no change in the pressure.

 

I can barely hear the pump run. How can I force the pump to continue to run when the engine is not running? Is this a wise thing to do? Wanted to dead head the pump.

 

 

You said way back at the beginning of this thread that you removed the line at the fuel pressure regulator and didn't see any fuel there.  Were you talking about the fuel line or the vacuum line?   Not seeing fuel at the vacuum line would be a good thing. 

You are going to need to get access to the fuel pump electrical connections at the fuel pump in order to test the connections for corrosion or not being tight.  Check the voltage with a known good voltmeter, and check the voltage with wiring still connected.  You should be seeing battery voltage.  If you are seeing battery voltage at the positive side of the connector, and zero volts at the ground wire, but the fuel pressure never rises into the required normal range, you have ruled out everything else, it must be the fuel pump.  I can understand the reluctance to condemn a part simply because there is nothing else.  I used to hate those situations, mostly because the only thing worse than being wrong was getting caught being wrong.

diyer2 Senior Enthusiast

diyer2

Posted
Posted
On 7/3/2019 at 11:53 AM, BruceK said:

Fuel pressure: 30-34 PSI, fluctuates at idle

 

On 7/3/2019 at 11:53 AM, BruceK said:

According to the manual the pressure is low should be about 60 psi

If you are keeping this truck replace pump and regulator.

Pump isn't fun I know.

Keep doing the hard starts and the starter will be next.

:)

BruceK Enthusiast

BruceK

Posted
  • Author
Posted
On 7/7/2019 at 8:50 AM, Doug_Scott said:

You said way back at the beginning of this thread that you removed the line at the fuel pressure regulator and didn't see any fuel there.  Were you talking about the fuel line or the vacuum line?   Not seeing fuel at the vacuum line would be a good thing. 

You are going to need to get access to the fuel pump electrical connections at the fuel pump in order to test the connections for corrosion or not being tight.  Check the voltage with a known good voltmeter, and check the voltage with wiring still connected.  You should be seeing battery voltage.  If you are seeing battery voltage at the positive side of the connector, and zero volts at the ground wire, but the fuel pressure never rises into the required normal range, you have ruled out everything else, it must be the fuel pump.  I can understand the reluctance to condemn a part simply because there is nothing else.  I used to hate those situations, mostly because the only thing worse than being wrong was getting caught being wrong.

Doug,

 

Removed and replaced the fuel pump. Pressure is now at 52 psi. Seems to be starting much better, but will set over night to ensure all is well.

BruceK Enthusiast

BruceK

Posted
  • Author
Posted
On 7/7/2019 at 9:11 AM, diyer2 said:

 

If you are keeping this truck replace pump and regulator.

Pump isn't fun I know.

Keep doing the hard starts and the starter will be next.

:)

Diyer2,

 

Removed and replaced the fuel pump. My only problem was that I could not find a plug and play replacement part. Have to cut my wiring harness and slave in a new connector. Fuel pressure is now 52 psi. Specifications call for 60 psi. Should I change out the fuel pressure regulator?

 

Bruce

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
59 minutes ago, BruceK said:

Doug,

 

Removed and replaced the fuel pump. Pressure is now at 52 psi. Seems to be starting much better, but will set over night to ensure all is well.

I generally turn the key on, close the door, then turn the key to start.  It's just what I have done since my pro-street days with dual 4bbl carbs and the electric back next to the fuel cell.  I even do that with my bike(except the door part, I shift bike into neutral, key had to be on to see the green light).  It gives the pump time to get the pressure up. 

Try removing the vacuum line from the FPR to see if there is any change.  What pressure you seeing with key on engine off?  You may have to get someone to turn the key on in order to see what the pressure is with the pump on engine off. 

 

It's good that you saw a big swing with the pump.  There is no word to describe the feeling when you aren't convinced it will work, and you even pause before trying it.  And then it all makes sense. 

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