What controls fuel pressure on our trucks?? - Ford Powerstroke Diesel Forum
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Old 05-31-2012, 06:46 PM
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What controls fuel pressure on our trucks??

I am getting 56-58psi at idle but as i accelerate the fuel pressur will drop below 20psi and the truck canbarely go over 40-50mph. If i lift off the throttle the pressure will build again but once I press the pedal it drops again. The fuel pump started whinning pretty loud so I thought it was the fuel pump. I just put in the new FORD fuel pump assy and it still does it. What else can cause this pressure drop? The new pump whines also but not as loud as the one I replaced. Could I have a bad new fuel pump?
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Old 05-31-2012, 06:56 PM
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http://napaautotech-classsupport.com...-TIPS-1WEB.pdf
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Old 05-31-2012, 07:11 PM
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Quote:
Originally Posted by leechiu View Post
I am getting 56-58psi at idle but as i accelerate the fuel pressur will drop below 20psi and the truck canbarely go over 40-50mph. If i lift off the throttle the pressure will build again but once I press the pedal it drops again. The fuel pump started whinning pretty loud so I thought it was the fuel pump. I just put in the new FORD fuel pump assy and it still does it. What else can cause this pressure drop? The new pump whines also but not as loud as the one I replaced. Could I have a bad new fuel pump?
Are you sure you got all those parts in correct? Some people claim to have parts left over sometimes, because they couldnt figure it out, or the parts weren't originally in the fpr....?

Sent from my SCH-I500
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Old 05-31-2012, 07:41 PM
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What controls fuel pressure?
The fuel pressure regulator.
Fuel is in the tank. Gets sucked up in the pickup assembly. Suction line. HFCM. The pushed to second filter. Then either the injectors or the FPR. Then return.
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Old 05-31-2012, 07:52 PM
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New fuel filters?
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Old 05-31-2012, 08:02 PM
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The fuel pump produces about 100psi. The fuel pressure regulator reduces it to 65psi (+/- 5psi) with the "new" blue spring (it is slightly longer than the stock spring).

Potential causes for reduced fuel pressure (assuming a good fuel pump):

The pickup in the fuel tank may have debris restricting fuel delivery causing a reduction in fuel pressure (look at your primary fuel filter for evidence of the debris such as this silvery material indicating fuel tank delamination):

...or the bypass valve may have broken off (the small orange nipple in the black housing to the left of the pickup screen on the middle tube):


And check that the fuel pump is actually connected properly...but fuel pumps aren't always good - and many actually don't think highly of the Ford fuel pump to begin with...also is this actually a NEW and ORIGINAL Ford pump or a reconditioned or eBay part? Sometimes the "cheaper" part is in fact CHEAP-O.

I hope this is a simple fix for you. The troubleshooting guide from Lilpooh is excellent!

Jonathan
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Old 06-01-2012, 05:15 AM
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Thanks for all the help!!! When it started acting up I did pull the fuel filters and they looked good as they only had 5-6K miles on them. The diesel fuel looked and smelled normal. I then did the blue spring upgrade and cleaned the EGR valve. The truck ran better than new for the few test runs after. The next day same exact problem but this time it had the P0611 FICM code. Overnighted a new FICM from Ed @ FICMREPAIR and installed. That fixed the P0611 code but the truck still acted up and would barely go over 40-50mph. So I pulled the filters again and same result all looked good. I went and bought a fuel pressure guage and thats when I found out that the pressure was dropping when accelerating. The stock pump was louder than normal when the problem started so thats why I changed the Fuel pump with a genuine Ford HFCM part. The new pump is louder than my original pump when it was new but not as loud as the original pump became when the issues started. I am just baffled at what can cause this fuel drop when accelerating. I can rev the motor in park and its fine but driving it will drop below 20psi. When I stop accelerating it will build pressure back into the 50+psi range. If I baby the throttle I can keep it in the 40-50psi range. The only thing I did not do is drop the tank which is probably next on the list. If anything will do the harpoon mod while it is out.
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Old 06-01-2012, 05:19 AM
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When you start going, the injectors use the fuel. In idle, they barely use any still.
The pump is not able to keep up with demand for multiple reasons.
Weak FPR. You fixed.
Weak HFCM. You fixed.
Next would be the supply to the pump. Like you said, the tank.
After that, filters.
After that, possibly clogged fuel lines, which would be weird.
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Old 06-02-2012, 10:17 AM
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Ok I think I found the cause. I wont know until I get the tank back in but the rubber foot that holds the screen and the bypass plug both were just floating around the bottom of the tank. I did the harpoon mod while I had the tank out. Here is a pic of the 2 pieces I found in the tank.


Now just have to figure out how to secure the foot and bypass plug so they dont fall off again.
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Old 06-02-2012, 10:36 AM
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That foot does just slip on the tube and you adjust to sit at the bottom of the tank so you can get all the fuel

as far as the bypass not sure how it is held in place ,,

but this wouldn't explain a fuel pressure issue but you may have sucked something up and created a blockage in the supply line??

Last edited by ZMANN; 06-02-2012 at 10:39 AM.
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