05 LS V6 Low fuel pressure

[Joseph Wood]

Yesterday my '05 Lincoln LS V6 was idling fine at a stop light, then went down from 1100 rpm idle to 400-500 -- very rough. When I tried to give it gas, it died or the rpms went down to 100-200 (had to restart it several times). Over the next couple hours, it wouldn't start up or would start up and quickly die.

I had it towed and after it towed, it started and drove about 100 feet without any problems. Then it wouldn't start again. My mechanic started it up and tested it and found it had 5 PSI on the fuel line, so he replaced the main fuel pump.

But, that didn't solve the problem. There is still only 5 PSI at the fuel rail, and a half a tank of gas. I was thinking the fuel sender might be bad, low fuel levels, bad fuel pressure sensor or bad connection at the pressure sensor or regulator? Any ideas? Right now it won't start. If I tow it, it will start and run for around 50 feet or so (maybe tilting the tank does something?).

Thanks you guys.

 

[1LoudLS]

when was the last time your fuel filter was replaced?

 

[Joseph Wood]

when was the last time your fuel filter was replaced?

When the fuel pump was replaced.

 

[joegr]

What about the secondary (jet) fuel pump in the driver's side of the tank? There's not much to fail there, but it has happened. When/if it does, then most of the fuel is pumped from the passenger's side to the driver's side, so no pressure for the engine.

Other possibilities would be the fuel pressure sensor. Just unplug the electrical connection and see if it runs mostly okay then. If not, it's not the sensor.
There is no regulator.
It could be the REM. The REM drives the fuel pump at whatever speed is needed to get the correct pressure range.

 

[cammerfe]

Joe, isn't the driver's side 'pump' a sort-of siphon that transfers gas from the 'auxiliary' driver's side to create a degree of balance, with all the engine-related activity coming from the pressure pump in the passenger side? I wasn't aware that there was ever transfer from passenger side to driver side. Am I wrong?

KS

 

[joegr]

Joe, isn't the driver's side 'pump' a sort-of siphon that transfers gas from the 'auxiliary' driver's side to create a degree of balance, with all the engine-related activity coming from the pressure pump in the passenger side? I wasn't aware that there was ever transfer from passenger side to driver side. Am I wrong?

KS

There is never any intentional transfer of fuel from the passenger's side to the driver's side, but if the jet pump breaks, that's what happens. The jet pump is powered by fuel pumped from the electric pump. If a hose ruptures or a coupling breaks, that fuel from the electric pump sprays out on the driver's side. It seems like something that would never happen, but it has at least a couple of times so far that I know of. It's a long shot, but something to check.

 

[Joseph Wood]

There is never any intentional transfer of fuel from the passenger's side to the driver's side, but if the jet pump breaks, that's what happens. The jet pump is powered by fuel pumped from the electric pump. If a hose ruptures or a coupling breaks, that fuel from the electric pump sprays out on the driver's side. It seems like something that would never happen, but it has at least a couple of times so far that I know of. It's a long shot, but something to check.

Could I test this by filling the tank to 3/4 full? Any overflow would just drain over into the passenger/pump side (or I may be completely out of my mind)?

 

[Joseph Wood]

There is never any intentional transfer of fuel from the passenger's side to the driver's side, but if the jet pump breaks, that's what happens. The jet pump is powered by fuel pumped from the electric pump. If a hose ruptures or a coupling breaks, that fuel from the electric pump sprays out on the driver's side. It seems like something that would never happen, but it has at least a couple of times so far that I know of. It's a long shot, but something to check.

Okay -- so I filled the tank and the engine started and idled nicely for about 15 - 20 minutes. I drove it for about 1 mile, then it died again. The tank is full (triple checked this) so there's always some fuel in the passenger side of the tank. The fuel pressure seems to drop down to around 5-10 PSI after about 5 minutes of driving.

This is a real head-scratcher. So, just to recap from the beginning:

I made a somewhat hard left turn and was accelerating out of the turn and had NO power. A couple little thumps came from the engine area (sounded like a misfire or something). I drove it for about a mile, and then at a red light the regular idle dropped to a very rough idle. Then when I accelerated out of the light, it just completely died. No power, super low idle. It went around 50 feet and just wouldn't start. At this time, the fuel gauge was reading 1/2 full.

I got the car towed to my yard and it started up and drove for about 50 feet, then died. It wouldn't start at all after that. No power. The next day, I towed it to my mechanic's and it started and we got it to move around 50 more feet. Revving the engine was very slow and low rpms though.

My mechanic replaced the engine pump, checked for error messages (several came up, such as low fuel pressure, something about the fuel line, etc.). He put around 3 gallons of gas and still couldn't get it started or running.

I then towed the car back to my place and figured if I filled the tank, I would be able to tell if it was the sender unit. Filled the tank, it idled fine for around 15 minutes. Then I drove it for around 1 mile, topping off the tank mid-drive. My car then died again. Zero fuel pressure -- even less response when I pumped the gas.

I'm all out of ideas at this point. I've tried disconnecting the fuel pressure sensor (no result), tapping and working on the sender unit. I can hear the fuel pump start up then stop when I turn the key to the on position.

So at this point, I'm thinking: bad replacement pump, bad fuel pressure regulator, or something else. Please help! Any ideas will help on this one.

 

[joegr]

Nothing that you have done has ruled out the jet pump.
Yes, the replacement electric pump could be bad too.
There's no reason to guess at it. You can check to see if the electric pump is moving fuel. If it is, then the jet pump is left as the suspect. You'll have to disconnect the line between the jet pump and the electric pump to see. (Dealers were troubled enough with this that they always replaced both pumps when there was a fuel problem under warranty.)

IF it is the jet pump, it's not that you run out of fuel of the passenger side. Take your garden hose and cut a big hole in the middle of it. You don't run out of water, but now very little of it ever gets to your spray nozzle. Same thing with a bad jet pump. Fuel just flows back into the other side of the tank. Now, all that said don't just replace the jet pump on my guess. Check for flow from the electric pump first.

 

[TooManyToys]

I just went through all this. Low tank, full tank, replace filter (cheap so what the heck), checking the Jet, used my spare main pump. It was the REM.