Low fuel psi WOT

[Karls03]

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. This is the first time I have ever seen this.

[kaya@bernhausen]

you can try replacing the spring, but if that fails you, you're gonna want to measure vacuum between the tank and the pump. anywhere above about 5"/hg indicates a restriction.
if that checks out fine, i'd say replace the hfcm

[Karls03]

Thanks, that's a good idea.

The weird part is that had I not looked down at the gauge, I wouldn't have known there was an issue. You would think that that radical of a pressure drop would be accompanied with a performance issue. Where's the low pressure oil read from? That could be used to verify the gauge isn't bonkers if the spring swap does nothing.

[RRF985]

My truck does the exact same thing. No loss of performance but man that pressure drops quick. I've basically stopped burying the loud pedal. I go until the psi get to 50 and then hold that. I thought about replacing the pump this next summer but we'll see.

[Karls03]

Thanks for the input. it's nice to know that I'm not the only one. I'd really rather wait till it's not so dang cold outside to do this, too.

[sgernon]

In the regulator, if you have the black "adapter" for lack of better word that the brass cup goes into make sure you have the seal on the end of it. It barely fits on it and if you pull the adapter out I think it typically falls off. I changed to the blue spring and did not know there was a seal there and the exact same thing happened you are describing. I fought it for weeks and even bought a new pump until I figured it out.

If by chance your pump is bad I do have a new pump motor I bought while troubleshooting I will sell for $165 shipped.

[Karls03]

Originally Posted by sgernon

In the regulator, if you have the black "adapter" for lack of better word that the brass cup goes into make sure you have the seal on the end of it. It barely fits on it and if you pull the adapter out I think it typically falls off. I changed to the blue spring and did not know there was a seal there and the exact same thing happened you are describing. I fought it for weeks and even bought a new pump until I figured it out.

If by chance your pump is bad I do have a new pump motor I bought while troubleshooting I will sell for $165 shipped.

How long did it it take for the psi to go bat crap crazy? This spring has been in since Feb '12. I had the Gillette spring in for about 2 years and never saw this.

[sgernon]

I didn't see the time for the spring mod. Mine acted up right away.

If I were you I would still pull it apart and confirm the seals are all properly in place. If they are I would also do a bubble test on the upper fuel canister to see if compression is getting in the system. You should also check for any debris in the fuel conditioning unit. If you see junk I would pull it apart and clean it out. If that all checks out I would then do a pressure test on the pump itself. I've never done this but am told they should put out ~100psi. If this is low you could check your tank for additional debris. If the pressure is low and everything is clean I would say the pump is not moving the volume and needs to be replaced.

[04cr450]

ahhh i just went through this on my truck! same issue, runs like a bad outta helkl but drops to 0-20 psi... well... replaced the pump($278.50 at tousely for the whole hfcm assembly).. replaced it and bam! truck idles at 72 psi and doesnt drop below 62 psi WOT... i have the srl tune as well... I CAN tell a difference in performance to.. Top end the truck keeps pulling where before you would feel it start to surge a little... replace your pump. Its cheap enough for good insurance anyways.

[Karls03]

Originally Posted by 04cr450

ahhh i just went through this on my truck! same issue, runs like a bad outta helkl but drops to 0-20 psi... well... replaced the pump($278.50 at tousely for the whole hfcm assembly).. replaced it and bam! truck idles at 72 psi and doesnt drop below 62 psi WOT... i have the srl tune as well... I CAN tell a difference in performance to.. Top end the truck keeps pulling where before you would feel it start to surge a little... replace your pump. Its cheap enough for good insurance anyways.

Does the separator come with this? I can't get any pics from Tousley's.

Where do you get the tool to remove the lines?