Air in the Fuel Rail | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

corakil

New Member
Joined
November 12, 2008
Messages
9
Reaction score
0
City, State
PA
Year, Model & Trim Level
1995 Ford Explorer sport
Hello there. I drive a 1995 Ford Explorer Sport 4.0L and I've been having a problem starting it after the engine is warmed up. The engine cranks and it almost starts but it seems like there isn't any fuel getting to the injectors.

I searched through several posts here and found several tips as to what maybe wrong.

I have checked the Intake Air temperature sensor and the coolant temperature sensor. Both of the sensors are fine as well as the electrical lines going to them.

I have also checked to see if I had pressure in the fuel rail by bleeding the shrader valve, believing that maybe the check valve on the fuel pump had gone bad.

There was definitely pressure at the shrader valve however after the initial spurt of gas there was a lot of air bleeding out as well. I bled the air out then went to start the truck and it started fine and ran fine. So I let it sit for 15-20 minutes and came back and tried to restart it and the truck wouldn't start.

So I went back to the shrader valve and bled it off again and I got the same thing as before. An initial spurt of gas and lots of air again.

Does anyone have any suggestions as to where the air would be coming from and how would I fix this problem?

Any tips or suggestions would be great and I thank you for taking the time to read this. ;)
 
Last edited:



Join the Elite Explorers for $20 each year.
Elite Explorer members see no advertisements, no banner ads, no double underlined links,.
Add an avatar, upload photo attachments, and more!
.





Did you check the FPR (fuel pressure regulator)? Its the round device on the fuel rail that has a vacuum hose attached to it. I'm thinking that if the diaphragm inside the FPR is broken, you could get air that way. If you pull the vacuum line from the FPR, you should not see any fuel; if you do, the diaphragm is broken.
 






i have not checked that but i will tonight appreciate the tip
 






well, even more bad news. Fuel pump just completely died. I'm wondering if that hasn't been the problem the entire time.
 






Probably was the fuel pump. You may want to check the FPR too, just because it is very easy to do and they do seem to fail infrequently. Usually if the FPR fails, it will cause the truck to run rich, so if you aren't seeing that, it is probably ok.
 






3 years ago I had my fuel pump replaced by a local mechanic and it appears that they had used electrical tape on the wires going to my pump instead of shrink wrapping them. The electrical tape broke down in the fuel and caused my pump to short out.

I got the fuel pump replaced and it seemed to fix my problems.

thank you guys for the help.


later on
 
Last edited:






okay so getting the fuel pump replaced didn't seem help. Apparently that just died in addition to my intial problem.

I'm going to check out the Fuel Pressure Regulator. I started it up again today and it was idling rough and I am almost certain it is due to air in the fuel rail again.
 






Have you put a fuel pressure gauge on it? Does the pressure bleed down quickly? Not many ways that air can get into the system. One would be if something is wrong at the fuel pump pickup, so that it is sucking air instead of gas. This would be more likely when the tank is low. Does it seem more problematic as the tank level drops?

Another thought is if the fuel is draining out of the fuel system (usually back to the tank through the fuel pump). As the fuel drains out, a slight vacuum would be created, and air could potentially be sucked in through a leak somewhere. In this scenario, the truck should run just fine, once the air is purged from the system (which should naturally occur once the pump has run long enough to purge the air from the system). Your original post indicated that once the air was purged from the line, it ran fine, so this scenario seems consistent with your symptoms. This is also why I asked if you've (or someone for you) done a bleed down test.

The only other possibility I thought of was "vapor lock." Usually we don't consider vapor lock a likely condition on a pressurized fuel system. Your original post indicated it seemed to be a problem at warm start. If the supply line were in contact with something hot (like an exhaust manifold), it is conceivable that, when the pump shut off, there would be a hot region where the line contacted the heat source, and the gasoline would vaporize. When the pump comes on again, it is feeding gasoline vapors to the fuel rail, which won't feed properly, and this will occur until the pump has run long enough to cool the hot spot and the gasoline stops vaporizing. A pretty outlandish scenario, and it should be pretty obvious on a visual inspection if this is a possibility.

All that said, the first thing I'd probably do no matter what the scenario is, would be to put a pressure gauge on it (no more "push the pin and see if it squirts") so I could better see what the fuel system was doing. You might also try to see if cycling the key helps, as the pump will run briefly each time you cycle the key.
 






Have you put a fuel pressure gauge on it? Does the pressure bleed down quickly? Not many ways that air can get into the system. One would be if something is wrong at the fuel pump pickup, so that it is sucking air instead of gas. This would be more likely when the tank is low. Does it seem more problematic as the tank level drops?

I am not seeing a difference if the tank is at Full or at a quarter.

Another thought is if the fuel is draining out of the fuel system (usually back to the tank through the fuel pump). As the fuel drains out, a slight vacuum would be created, and air could potentially be sucked in through a leak somewhere. In this scenario, the truck should run just fine, once the air is purged from the system (which should naturally occur once the pump has run long enough to purge the air from the system). Your original post indicated that once the air was purged from the line, it ran fine, so this scenario seems consistent with your symptoms. This is also why I asked if you've (or someone for you) done a bleed down test.

I just put in a brand new fuel pump in it so i'm pretty sure the check valve on the pump is fine.

The only other possibility I thought of was "vapor lock." Usually we don't consider vapor lock a likely condition on a pressurized fuel system. Your original post indicated it seemed to be a problem at warm start. If the supply line were in contact with something hot (like an exhaust manifold), it is conceivable that, when the pump shut off, there would be a hot region where the line contacted the heat source, and the gasoline would vaporize. When the pump comes on again, it is feeding gasoline vapors to the fuel rail, which won't feed properly, and this will occur until the pump has run long enough to cool the hot spot and the gasoline stops vaporizing. A pretty outlandish scenario, and it should be pretty obvious on a visual inspection if this is a possibility.

Not quite sure about this. I mean it is a possibility but I would think the odds on it are pretty long. As a previous poster stated do you think if the diaphram in the FPR is bad that it would allow air back into the system?

All that said, the first thing I'd probably do no matter what the scenario is, would be to put a pressure gauge on it (no more "push the pin and see if it squirts") so I could better see what the fuel system was doing. You might also try to see if cycling the key helps, as the pump will run briefly each time you cycle the key.

As much as I enjoy getting a facefull of gasoline I am seeing now that I need to pony up the money to buy a fuel pressure gauge.

I am also seeing a drastic drop in my miles to the gallon I am getting. I don't know if that helps at all.
 
Last edited:






One would like to think that a brand new pump would have a good check valve. Maybe it's just the engineer in me, but I personally would want to see the fuel system hold pressure before I could declare the check valve good.

Yes, the odds are pretty long on the vapor lock thing. At the same time, the only thing hot enough would be the exhaust, and it should only take a minute to see if the fuel supply line has somehow got bent up against the exhaust manifold.

A ruptured FPR diaphragm could allow air back into the system, but at the same time, it would normally also allow gasoline to leak into the intake when it's under pressure. You haven't indicated finding gasoline in the vacuum line to the FPR. If you haven't checked that out, yet, that would still be a good idea, in addition to putting a fuel pressure gauge on it.
 






pulled the fuel line on the FPR and found gas in the vacuum line. Replaced the FPR and all is well. Bought the fuel gauge and after i replaced the FPR it seems to hold steady at 44 psi.

Thank you guys for the help much appreciated.
 






Back
Top