Vapor lock on in tank pump?

[Map63Vette]

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?

 

[funwithfuel]

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.

 

[5.7 hemi]

Is the tank vented somehow, vented gas cap or line vented?

 

[67Dart273]

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.

 

[RedFish]

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.

 

[Map63Vette]

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.

 

[RedFish]

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.

 

[funwithfuel]

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.

 

[Map63Vette]

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.

 

[TrailBeast]

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.

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.

 

[funwithfuel]

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.

 

[toplscuda]

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.

 

[Map63Vette]

So I realize this is a really old thread to bring back, but I had this issue pop up two more times on me. The first time a couple of months ago. Similar symptoms where I had gotten off the highway and was driving through town back home while making a stop for coffee and the radiator fans had kicked on a few times. Car just tapered off on idle and died. Got it restarted a few times, but it wouldn't run for more than a minute. Went back later that evening and started it up and drove it home with no issues. Fast forward to yesterday and had the same thing occur, but this time I had mounted a fuel pressure sensor so I could record it and see it on my dash display after the earlier failure a couple of months back. Oddly enough, if I just turned on the fuel pump and let it run continuously, it would build pressure and hold it, but when I started the car and had it running, the pressure would fall away until the car died within a minute or so. Went back after a couple of hours and it started up and drove home just fine again. So I think the pump is just weak and can't keep up the flow at pressure when it gets hot or something. I don't think it's a relay issue as I would expect that to be on/off type behavior if it was failing, not pressure that starts high and falls away. Same thought on the computer output that drives the relay. A weak transistor in the computer wouldn't cause reduced current output at the relay. I guess it's still possible there is some kind of issue in the wiring on the main power side, but since it seems to build to full pressure and hold it when the engine is not running, I would think that means it can pull enough current. I've been through that so many times and have likely way oversized wire for the job (I think it's 10 or 12 gauge at this point). I did find out the original wiring for the pump through the bulkhead plate sucked though. It was in a plastic fitting that had started melting, so I replaced it with bulkhead style studs. I'm thinking I may have just had a non-ideal fuel pump for a while now, just surprised it's only acted up a couple of times in all the years I've had it.

 

[1MeanA]

I have heard of a bad ground causing this symptom.

 

[Map63Vette]

I have heard of a bad ground causing this symptom.

I've tried that a couple of times and rewired the whole thing as well. Originally I actually ran full length power and ground wires for the pump, both of heavy gauge wiring. When I redid the wiring passthrough on the pump plate I changed the design a bit and made a pigtail to convert from the ring terminal fittings on the pump bulkhead to a sealed connector so it would be easier to drop the tank in the future. I also moved the wiring to run through the cabin instead of under the car. I can't recall if I went back to a chassis style ground at that point or not, but it's definitely something I have looked at. The fact that the pump melted the original plastic passthrough kind of makes me wonder. The wiring on the tank side seemed way undersized for the pump (like, 16-18 gauge), though in theory the pump should only be pulling ~8-10 amps. I went ahead and rewired it with larger stuff when I put in my new passthrough studs. Way back when I first did the fuel injection install I had a little power distribution unit for my computer that would melt the fuse holder for the pump without actually blowing the fuse, which never made any sense to me either. I haven't noticed any more fuse issues since I rewired the car and put in my new fuse/relay panel though, but I guess it can't hurt to check it again. I think I even put an ammeter on the line at one point to verify current draw. I'm limited to only being able to read 10A, but I was pretty sure it was below that when I checked it.