Vapor lock on in tank pump?

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Map63Vette

Map63Vette

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So I was cruising home from work today and as I was about half way through town after getting off the highway my car bobbled on the idle just a bit and then just died. At first I thought the idle drop may have been the electric fans kicking on, but obviously it wasn't because it flat out killed the car and it wouldn't restart. The thing I don't get is that I'm running an EFI setup with an in tank pump. I've got a 5.7 hemi and a standard Walbro 55GPH style pump (different brand though). I got the car pushed into a parking lot and went about checking wires and whatnot because I figured I may have just dropped a sensor or something. Keyed the car over a few times to prime the fuel pump and the fuel pump relay was clicking and I could swear I heard the fuel pump cycle, but I had no pressure on the gauge on my regulator. Got a ride home and went back a few hours later with tools and the car started up like nothing was ever wrong.

Has anyone ever heard of vapor lock on an in tank pump that runs 60 psi at the rails? I know the lines run near my headers a little where they come up at the back of the firewall. The system splits at the firewall (one line to each rail), then from each rail into the regulator and back to the tank. Any ideas what I might be able to do to prevent the problem or get the car started if it happens to me again?
 
I would set up a jumper wire with a fuse rated for your pump. Roll around close to home, when it acts up, place the jumper in place of the relay. If you regain your fuel pressure , its your relay, If you don't hear the pump with the relay jumped and have no fuel pressure, most likely , your pump has failed. Check all your connections, power ground etc... Good luck.
 
Is the tank vented somehow, vented gas cap or line vented?
 
I would suspect the relay, the power feed, or the pump. "Hearing it click" does not mean you have power to the pump

Maybe you should run a temporary indicator lamp from the pump terminal up where you can see it, you can run it up through the trunk, under the seat, and just put it somewhere that you can turn around in case of trouble.
 
It's more likely the pump kicking off dues to temperature. I've seen it a few times.
My juniors Honda Accord was one. The pump would run ( although a bit noisey ) for an hour or so. The engine didn't run great but drivable until ithe pump kicked off.
After a few minutes the car would start and run like crap for maybe 30 seconds. Let it sit overnight and go driving again.
New pump cured it.
 
Yes, the tank is vented. It has a vent port on the flange and I think the gas cap is a vented style as well. I swear I could hear the pump whirring in the tank when I keyed the power a few times. I had the door open and was listening pretty close and it sounded like it normally does. The whole tank and pump are brand new. I thought about just jumping the relay to keep the pump permanently on, probably wouldn't be a bad idea to keep something to make that easier. Right now the computer is set up to prime the pump for two seconds when the key is turned on, then it shuts off until it sees an rpm signal while cranking when I can hear the relay click on again.
 
There may be a component failure at the pump too. Some aftermarket pump assemblies have soft parts that will turn to jelly in our fuel. So the pump runs and sounds fine but its not getting the fuel into the fuel line.
 
How is your pump outlet secured to your supply nipple ? Perhaps the connecting hose has blown off allowing fuel to pump up and out back to tank sump or possibly a ruptured hose doing the same thing. Do you have a pulse damper on the pressure side of the pump. What type of pressure regulator are you using. Mechanical or vacuum. If a vacuum is used apply 20" vac and see if your pressure doesn't rise slightly. If mechanical, try capping the return the run the priming cycle and observe your pressure. I believe, by your description, you'll find a leak at the pump in the tank.
 
Hmm, not sure how the pump is connected since I bought the whole tank as a unit. My guess is that it's just a rubber hose clamped on both ends so that you can replace the pump fairly easily. It's an Aeromotive adjustable regulator with a vacuum reference. It started up fine after sitting for a while and drove around like nothing was wrong yesterday, so I don't think it would be a broken line or I would think it wouldn't be working at all. When I went back to it the day it messed up after a few hours and keyed it over it went right up to full pressure again, which is why I thought maybe vapor lock since it was a temporary problem (I didn't touch anything between letting it sit and going back to it later), but I'd never heard of that on a high pressure in tank pump.
 
Even if it was possible to get a vapor lock in a constant flow system, you still would have been showing pressure at the gauge (Air pressure, but pressure none the less)
I'd bet ya it's the pump or power supply to it.

Map63Vette said:
Hmm, not sure how the pump is connected since I bought the whole tank as a unit. My guess is that it's just a rubber hose clamped on both ends so that you can replace the pump fairly easily. It's an Aeromotive adjustable regulator with a vacuum reference. It started up fine after sitting for a while and drove around like nothing was wrong yesterday, so I don't think it would be a broken line or I would think it wouldn't be working at all. When I went back to it the day it messed up after a few hours and keyed it over it went right up to full pressure again, which is why I thought maybe vapor lock since it was a temporary problem (I didn't touch anything between letting it sit and going back to it later), but I'd never heard of that on a high pressure in tank pump.
Click to expand...
 
sounds more n more like pump or pump relay. I ='d definitely go after the relay first since it's cheaper and loads more accessible.
 
I'm betting pump also. Had a Beretta once that would do that at the most inoportune times, like going through neighborhoods you really don't want to be in in the first place. I think I replaced the punp in that car about once a year.
 
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