Low fuel psi WOT
 

2003, 104K, Blue spring (Feb 2012), SRL tune, ~4000 on fuel filters, cruise at 60~64 psi on Auto Meter Sport Comp gauge.

I was rolling into the throttle and noticed a little gauge flutter (mid 50s), then it FELL to 40 psi! Immediately lifted.

On the way home I thought that I would try again, 3/4 throttle, doing good, repeat. Screw this! Standing start, WFO, let's see where it goes. At the top of 5th there was a little flutter. Into 6th it dropped like a turd in a septic tank! Pulled normal, sounded ok, but it fell to damn near 20 psi this time.

Now I SERIOUSLY think it's related, but up until 2 weeks ago the fuel psi was pretty steady, drop into the mid 50s on the loud pedal, then I did some RevX. All of the usual good things happened, but I also noticed fluttering of the gauge sitting in the driveway during spool down.

I'm thinking that the Gillette spring may have to go back in, especially since I wrote in Feb that the Blue spring was 65~70 at cruise, now it's 60~62. This is the first time I have ever seen this.

The stiffest spring in the world wont make up for a lack of volume though. If it's dropping at WOT to 20psi, a stiffer spring wont help as the stock or blue spring is already not even opening at that pressure.

Yeah, I think you're right. I've been mulling it over and I think it's the fuel pump. Can that be purchased seperately or do you have to get the entire assy from Tousley's?

Oh yeah, where can I get that tool to remove the fuel fittings?

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What size was the water separator drain Allen? Figure I'll drain that dude first. Yeah, yeah, Bad Karl, I know.

Hey, I found the p/n you posted for the knurled replacement on my own. :tu:

yes you can purchase just the pump. Me and Mdub had a thread about it ill see if i can link it. it also has link to 2 pumps that replace just the rail mount pump in the rail mount fuel pump/water separator.

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https://www.dieselbombers.com/ford-p...fuel-pump.html

one of the fuel pump links in the first post of the thread i linked also has directions on how to change it.

MKM says that their sump is only for use with after market lift pumps, any inputs? Personally, I think it would HELP the OEM pump.

i can tell you that even with an AD100 and sump my FP will drop to +-50psi under full throttle right now because my stock pump is weak. But i do think a sump is a good idea for any fuel system. Even airmotive says to use one with their pumps.

The allen is 6mm for water seperator. When you did the blue spring did you put that tiny oring on the little plunger in the housing? you have to stretch it on there, without it it won't hold pressure right :w2:, dont' ask how I know. Also it doesn't hurt to pull the whole pump housing out and give it a good cleaning, you won't believe the junk you will find in there. you have to make sure the tool to remove the lines is for Ford, should be able to find the ones for fuel lines at parts store.

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That plunger is only on the 03-04 trucks, nwere ones are different.

Looks like everyone got you the answers you need already Karl.

:c:

Thanks for all of the inputs! :tu:

I've heard about the little oring, but because it has been in for 10 months and just now starting to act up, the o-ring could be ruled out. Considering that I ONLY bought the spring, I reused what ever was in there. I read that if you leave out that o ring, there will be a radical drop immediately after install.

After re-reading when I put the Blue spring in, it has been slowly loosing psi. When initially installed it was at 65~70 at cruise. Today it's 60~62 at cruise. As previously stated, there has been some fluctuation in the needle when spooling down on what has usually been a rock solid needle.

My plan was to remove the entire HFCM, clean, r&r pump then re-install assy.

Yea i need to get off my butt and put the fuel pump in my truck. (would help if i ordered one.)