Fuel Pressure
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New User
Joined: May 2003
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From: MI
Fuel Pressure
I have a 97 F-150 4X4, 4.6 auto. I keep getting codes 171 and 174 fuel system too lean banks 1 and 2. I checked the fuel pressure and its only 22 lbs at the fuel rail. I hear the pressure should be around 40 lbs. I just want to verify with someone what the normal pressure is. Would this cause the too lean condition at 22 lbs?
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
Fuel Pressure
Hi finster725 and welcome to FTE 
The fuel pressure should be 30-45 psi. At idle it should be 30ish, if you remove the vacuum hose to the regulator it should be 45ish. Yes 22psi can cause a lean condition. How old is your fuel filter?
To check the pump you need to take a blocked off fitting and plug the return line and then see what pressure you have.
If it is ok then you need a new regulator.
Let us know what you find please.
The fuel pressure should be 30-45 psi. At idle it should be 30ish, if you remove the vacuum hose to the regulator it should be 45ish. Yes 22psi can cause a lean condition. How old is your fuel filter?
To check the pump you need to take a blocked off fitting and plug the return line and then see what pressure you have.
If it is ok then you need a new regulator.
Let us know what you find please.
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New User
Joined: May 2003
Posts: 9
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From: MI
Fuel Pressure
Replaced fuel filter and still get 22 psi. Plugged return line and still the same reading. Sounds like pump is going bad or possibly plugged pickup screen? I'll drop the tank tomorrow and see what I find.
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New User
Joined: May 2003
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From: MI
Fuel Pressure
I dropped the tank to replace the pump, but when dropped the tank, I either broke off or was already broke, an electric connector of some type on the back - top of the tank. Does anyone know what this thing is? It has an electrical plug with 3 wires , it is flat on top with short unit that goes into the tank. Looks like maybe a vent valve or something?
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
Fuel Pressure
That sounds like your fuel tank pressure sensor. It tells the PCM how much pressure is built up inside the tank so it knows if there might be a vapor leak which would cause excess evaporative emissions. If it was already broken before the check engine light should have been on.
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New User
Joined: May 2003
Posts: 9
Likes: 0
From: MI
Fuel Pressure
Replaced the fuel pump and screen (and the fuel tank pressure sensor). All fuel pressures are back to normal. The truck runs like I just put a turbo on it. The pump must have been going bad for a while. No check engine light so far. Looks like the problem is fixed!
Anyone who gets codes 171 & 174 should check the fuel pressure to make sure it is within range.
Anyone who gets codes 171 & 174 should check the fuel pressure to make sure it is within range.
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