Help!!! Random loss of fuel pressure????
05-06-2014, 08:50 PM
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Help!!! Random loss of fuel pressure???? I have a 5.3 with a Ls6 intake manifold/fuel rails, Tanks Inc Pa-4 In tank fuel pump with Walbro 255, and lS9904 filter/regulator. I noticed that when I drive it on hot days it stalls out. The fuel pressure starts out at about 60 then one of the first things I notice is the fuel pump gets louder, then the fuel pressure starts to drop till the car dies which takes about 10 sec. After it dies it's starts right up every time but the fuel pressure won't hold. When this happens it only primes to between 40 and 50 then drops back down till the engine dies. After the initial stall it wont run for more than five seconds, so I just leave it. But after a few hours, when the sun goes down and everything has cooled off, I go back to get it, and it starts right up and I drive it home like nothing ever happened. Any Ideas?
05-07-2014, 06:41 AM
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You could also be experiencing vapor lock and might need to insulate your fuel lines. Note that we're just coming out of winter and the winter blend of fuel is more susceptible to vapor lock until it's used up. Can imagine what the carburetor guys are going through with the lower pressure.
05-07-2014, 08:19 AM
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The 1st time this happened I didn't have the gas cap installed because my vent fitting hadn't arrived yet. And now it's properly vented. So I don't think it's the vent but I will check.
As for vapor lock I have always thought that's what it was. But one day I left it running in my driveway for a while but nothing happened. I know this doesn't mean it's not vapor lock. But I would like to know before I start replacing stuff. I have all steel braided line and it runs up about 5 inches from the long tube headers. So vapor is a strong possibility. Is there any way to know that that's what it is with absolute certainty? And what could I do to prevent it?
As for vapor lock I have always thought that's what it was. But one day I left it running in my driveway for a while but nothing happened. I know this doesn't mean it's not vapor lock. But I would like to know before I start replacing stuff. I have all steel braided line and it runs up about 5 inches from the long tube headers. So vapor is a strong possibility. Is there any way to know that that's what it is with absolute certainty? And what could I do to prevent it?
05-07-2014, 08:50 AM
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Yesterday when it happened I disconnected the fuel line and let the fuel run into a bottle and primed it a few times to let fresh fuel in the lines. Then hooked it back up and it still did the same thing. So that's what makes me think that it's not vapor lock.
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05-08-2014, 08:21 PM
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05-08-2014, 09:55 PM
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05-09-2014, 08:30 AM
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The pressure is reading at the rails. I think I'm gonna convert over to the flow through, but I didn't want to spend $400 doing the conversion then realize that it was the pump the whole time.
05-09-2014, 08:40 AM
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Yeah I was thinking the same thing. Vapor lock at 60 psi is hard to do. I let it run in the driveway yesterday, after about 5min the pump started sounding like an F16 powering up, and the fuel pressure started dropping till the engine stalled out. So now I'm thinking it's the pump. I ordered a new filter/regulator so if that doesn't fix it then next is the fuel pump.
05-12-2014, 09:43 PM
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Ok so I got the filter/regulator in today and installed it. The first thing I noticed was that it never reached 59psi, it stuck around 52-54 but ran fine. So I let it run in the driveway for a while to see if it would stall, and it eventually did. After it stalled I dropped the tank and removed the pump assembly. I put it in an ammo can, put a little gas in, and hooked it up to a battery to let it run, it ran fine. then I hooked it up to the car and let it run and it stalled out again. I'm not to sure what's going on but I think the pump may be going out. I also cut open the old filter and didn't se anything other than grime. I ran a magnet over the dirt and it stuck, so it could be metal shavings. Here is a link with the pump running the car from the can. Never mind the broken return line fitting, I did that when I was taking it apart. Do you think the pump is going out?
05-20-2014, 05:52 PM
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A few things:
1) If heat caused this problem the WORST thing you can do is change the way you have it plumbed to flow through the rails to the FPR, then return to the tank. The way you have it plumbed should minimize the amount of underhood heat getting into the fuel
2) From watching your video that pump is toast. Replace it and begin troubleshooting again or you'll get nowhere.
3) After the new pump is installed and you go for a drive, when the car gets to the point where it's dropping pressure shut it down and pull off. Take a sample of fuel out of the tank and measure its temperature. If it comes back over 130F you have a problem with hot fuel. All fuel pumps lose their ability to move fuel as the fuel itself heats up, some MUCH more than others. The Walbro 255 is pretty good about it (make sure you really have a Walbro 255). The pump running doesn't cause heat like that (unless you're running around with 1 gallon of fuel in the tank), heat transfer from the exhaust, engine, etc does. Location of fuel lines and the FPR will have more to do with it.
4) That lS9904 is the C5 Corvette combo regulator/filter. It's a reliable unit but the pressure can fluctuate depending on how hot things get. It won't cause all fuel pressure to drop off and stall the car though.
5) How are you powering the pump in the car, and in the ammo can?
1) If heat caused this problem the WORST thing you can do is change the way you have it plumbed to flow through the rails to the FPR, then return to the tank. The way you have it plumbed should minimize the amount of underhood heat getting into the fuel
2) From watching your video that pump is toast. Replace it and begin troubleshooting again or you'll get nowhere.
3) After the new pump is installed and you go for a drive, when the car gets to the point where it's dropping pressure shut it down and pull off. Take a sample of fuel out of the tank and measure its temperature. If it comes back over 130F you have a problem with hot fuel. All fuel pumps lose their ability to move fuel as the fuel itself heats up, some MUCH more than others. The Walbro 255 is pretty good about it (make sure you really have a Walbro 255). The pump running doesn't cause heat like that (unless you're running around with 1 gallon of fuel in the tank), heat transfer from the exhaust, engine, etc does. Location of fuel lines and the FPR will have more to do with it.
4) That lS9904 is the C5 Corvette combo regulator/filter. It's a reliable unit but the pressure can fluctuate depending on how hot things get. It won't cause all fuel pressure to drop off and stall the car though.
5) How are you powering the pump in the car, and in the ammo can?
05-30-2014, 11:55 AM
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The lines wires and lines where still hooked up when the pump was in the ammo can.
I got the new pump in last week, I ordered an Aeromotive stealth 340 this time because I heard there was a bunch of fake walbros out there. After I installed it it seemed to run fine but the pressure was too high (67-69). So instead of ordering another Ls filter/regulator, I got the holley billet aluminum regular and filter instead.
A couple things that may have caused the last pump to go out was the wires where way to small, probably 18-20 gauge. And the pump was really close to the bottom of the bowl, possibly causing the flow to be resricted. So I got a fuel pump relay kit with the 10-12 gauge wires and made sure there was no restricted areas around the pump.
I should be done installing everything today.
I got the new pump in last week, I ordered an Aeromotive stealth 340 this time because I heard there was a bunch of fake walbros out there. After I installed it it seemed to run fine but the pressure was too high (67-69). So instead of ordering another Ls filter/regulator, I got the holley billet aluminum regular and filter instead.
A couple things that may have caused the last pump to go out was the wires where way to small, probably 18-20 gauge. And the pump was really close to the bottom of the bowl, possibly causing the flow to be resricted. So I got a fuel pump relay kit with the 10-12 gauge wires and made sure there was no restricted areas around the pump.
I should be done installing everything today.