P0171/P0174 - Already replaced almost everything

[blue89bird]

99 Explroer 4.0 SOHC with 130k on it

Got an P0171/P0174 a while ago and have been researching causes. Yesterday I did the following:

Replaced upper and lower intake gaskets
Cleaned MAF
Cleaned IAC
Cleaned throttle body
replaced PCV valve
Checked all vacuum hoses I could see

Start truck- starts right up and it runs great for 10 mins, then the CEL lights back up and the symptoms are back (hard to start, a bit of a stumble when driving)

Next on the list is changing the fuel filter and hooking up a fuel pressure gauge to make sure it's building/holding the correct pressure.

Anything else I'm missing here?

 

[my98nnj]

Make sure the egr is working correctly. Disconnect the valve and see if it changes anything.

 

[blue89bird]

Make sure the egr is working correctly. Disconnect the valve and see if it changes anything.

I pulled the vacuum hose of the top with no change.

 

[SoNic67]

You need to apply vacuum on it. Suck (with your lungs) using a small hose attached on the diaphragm stub. Idle RPM should drop.

 

[blue89bird]

I tried with a piece of tubing I had (though it was oversized and didn't make a good seal) and nothing happened. I pulled it from the motor and put my mouth right on the stub and could feel it open and close with vacuum though. I cleaned it anyway. The battery was unhooked so the CEL is off at the moment but I'm going to drive it this afternoon and see if it comes back on.

I did just find a small crack in a vacuum hose under the battery. It was on the tube with the orange label, labeled:

F77E-9G271-BD
THIS END TO VALVE
PA12 ETFE (081)

I wrapped it up with electrical tape really good as a temp fix to see if it does anything

 

[blue89bird]

and the light it back! I'm ready to torch this thing

 

[2000StreetRod]

Lean condition procedure

Lean condition procedure

 

[blue89bird]

Hooked up a fuel pressure gauge. With key on and not cranking it doesn't show anything. After it starts it goes to 35-37 PSI. Turn the key off and it drops like a rock to 0

Does this help?

 

[blue89bird]

should also note that i replaced the fuel filter. The above findings were the same before and after.

 

[snoranger]

Hooked up a fuel pressure gauge. With key on and not cranking it doesn't show anything. After it starts it goes to 35-37 PSI. Turn the key off and it drops like a rock to 0

Does this help?

Thats a problem.

Thats too low.

It shouldnt do that.


Looks like your going to be dropping the tank or cutting an access hole.

 

[blue89bird]

Thats a problem.

Thats too low.

It shouldnt do that.


Looks like your going to be dropping the tank or cutting an access hole.

Awesome considering I just filled it up today!

What should the pressure be? Is there anything else it could possibly be? Clogged fuel line? If it won't prime with the key in the ignition is there a relay or something I can check? It seems to run fine once it starts.

 

[2000StreetRod]

Ford Explorer Fuel Pump Electrical Procedure

Ford Explorer Fuel Pump Electrical Procedure

 

[blue89bird]

I'm about 99% sure it needs a fuel pump. Put the gauge on it just now and when I key on but don't crank it jumps to 25-30 and then just drops like a rock. If I crank it, the pressure builds up while it cranks (5-10 seconds) and when it builds up it starts right up and hovers at 35lbs. If I key on, key off 2 times to build up pressure and crank it when the pressure is up it starts right up. Looks like the regulator built into the pump has crapped out or something.

 

[jremington59]

You should run through the steps 2000StreetRod left in his post. I don't understand how you have 37 pounds of pressure when it's running, but none with key on. If I recall you should have 56 to 72, so it's quite low.

 

[snoranger]

You should run through the steps 2000StreetRod left in his post. I don't understand how you have 37 pounds of pressure when it's running, but none with key on. If I recall you should have 56 to 72, so it's quite low.

The rubber hose from the pump to the top of the sender assembly is known to crack. A small crack in that hose can cause the symptoms described.

 

[blue89bird]

The rubber hose from the pump to the top of the sender assembly is known to crack. A small crack in that hose can cause the symptoms described.

Do you have a picture or diagram of The hose that you're talking about?

 

[snoranger]

Do you have a picture or diagram of The hose that you're talking about?

See the rubber hose between the pump and regulator, then to the solid tube? That could cause your problem.... Thats not the only thing that can cause your problem.

 

[blue89bird]

Thanks. If I have to drop the tank the pump is getting replaced regardless.

 

[snoranger]

Thanks. If I have to drop the tank the pump is getting replaced regardless.

Smart man.

 

[blue89bird]

Any suggestions for dropping a full tank without killing myself or do i just drive it for 200 miles and pray it doesnt die.