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Discussion Starter · #1 ·
My fuel setup:

  • Aeromotive 340lph pump, 10ga wiring - directly to the battery. No dual-stage voltage.
  • Boomba Fuel Rail
  • FIC 1100s
  • AEM FPR
  • ~38psi base pressure
A week ago, everything was kosher with my fuel setup.


Then just the other day, I started leaning out big time under high rpm WOT. Leaning out as in 14:1 or leaner.


First I tried maxing out the injectors. That didn't help much...maybe got me down to the high 13s.


So we temporarily ran a fuel pressure gauge "in-car". My fuel pressure would spike to ~70psi and then fall all the way back down to around 40psi and stay there. I'm not sure what my max fuel pressure was before (since I didn't have an in-car gauge), but it should have been around 70.


Next, we measured voltage at the fuel pump. It stays at around 14v.



Just for grins, we bumped the base fuel pressure up to 65psi. It would then spike to 70 and then drop down to around 45psi.


So for some reason, I'm losing fuel pressure all of a sudden under heavy load. There are no obvious leaks and we don't smell fuel. There could be a leak in the tank, for all I know - haven't checked that yet.


Anyone have any ideas?


Guys with big fuel pumps and in-car gauges - what peak fuel pressures are you seeing? What's your base pressure?
 

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My base pressure (Under Vacuum) is 43psi with the stock FPR. As of now I ditched the BlaqOps progressive controller because for some reason it decided it was union and would take breaks 5 times a day for nearly an hour each time. Now I have 2 stock pumps connected to a Y fitting and one comes on with a Hobb's switch at 5 psi. It actually works quite well, no spikes of too rich fueling.

Your issue sounds like you are either;
A) Over running the FPR (Which I kind of doubt)
B) You have a leak in the tank thats releasing pressure (Most likely)
 

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B) You have a leak in the tank thats releasing pressure (Most likely)
I'm going with a split fuel line in the tank, between the pump and the hanger. It happened to me... it could maintain fuel pressure under light throttle, idle ok... yet couldnt deliver under boost. BTW many fuel pump kits have a standard hose clamp and not a fuel line clamp. A standard hose clamp cuts into a line when tightened hard... where a fuel line clamp is smooth. Pic below....
 

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Discussion Starter · #4 ·
Your issue sounds like you are either;
A) Over running the FPR (Which I kind of doubt)
If I "over-ran" the FPR, my pressure would be too high, not too low.

B) You have a leak in the tank thats releasing pressure (Most likely)
This is my best guess at this point as well. I guess it could be on the feed or the return side.

What's your fuel pressure @ WOT?
 

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Interesting. Could you tell me more of your symptoms?
Well, it didn't go from being a-okay to lean... but more gradual(slowly splitting). No gauge in the car to see it fluctuate. Slowly over time(maybe a tank of gas or 2, not too long) it started getting leaner and leaner... progressively worse as time passed. It takes about 10 minutes to pull the hanger out. I would pull it, and examine the entire fuel line.. b/c it doesnt always make itself obvious. Bend it around, flex it... to make sure no slit reveals itself.

double check vacuum line to regulator?
Wouldnt hurt to check it(easy as poo)... doubt it's this, as it hits 70psi then falls though.
 

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I seen the issues sometimes with the MAF going out. The voltage would be correct but the frequency would change and it would be going bad. Dumping fuel via fuel map did not help.

But again it might be a fluid leak in tank as Holly stated. I doubt you over run a FPR on that setup.
 

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If I "over-ran" the FPR, my pressure would be too high, not too low.

This is my best guess at this point as well. I guess it could be on the feed or the return side.

What's your fuel pressure @ WOT?
"Over ran" is something I used to see on some of the older Evos and DSM's when people would use a modified 255 in the tank and a in line 044 or similar set up. Basically the volume would just hold the FPR open and the pressure from the manifold couldn't push the FPR back down to maintain the 1:1 ratio. Everything would just keep on trucking at 40psi or so right on through.

My pressure WOT @ 24psi is just under 70psi or so. I see about 80 max if I'm cranking the boost up. With yours I would just put some new fuel line and clamps on your hanger and see if that fixes it.
 

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Discussion Starter · #11 ·
Well, it didn't go from being a-okay to lean... but more gradual(slowly splitting). No gauge in the car to see it fluctuate. Slowly over time(maybe a tank of gas or 2, not too long) it started getting leaner and leaner... progressively worse as time passed. It takes about 10 minutes to pull the hanger out. I would pull it, and examine the entire fuel line.. b/c it doesnt always make itself obvious. Bend it around, flex it... to make sure no slit reveals itself.
Will do.
 

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Discussion Starter · #12 ·
Pulled the fuel hanger assembly out today. Some points of interest:

  1. The fuel in the hanger assembly was black. Meanwhile, the fuel in the actual tank appeared normal.
  2. The fuel pickup sock was black and filthy
  3. The o-rings in the tank looked fine.
  4. The pump itself looked fine.
  5. The internals of the FPR looked fine.
  6. The input side of the Jeg's inline fuel filter was black, but the output side of the filter was clean.

During a phonesex session, Hollywood pointed out that since the fuel in the tank was clean but the fuel in the pickup was dirty, it was likely something in the return line that was contaminating things.

The only thing we changed recently was we shortened the length of the -6AN line. It's possible that we missed some rubber debris from inside that line before it was reinstalled. We always blow them out with the air gun, but who knows. Aside from that, I don't know what could have caused this.

I'm hoping that once this is 100% clean, my fuel pressure issue will subside. After all, it didn't begin until a couple of days after we shortened this line.

I'll have to see if I can find a new sock filter locally and give it a shot tomorrow.
 

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any update on your issue? Im thinking whatever is wrong with yours is the same as mine.
 

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Discussion Starter · #15 ·
Wow, blast from the past.

IIRC, cleaning the system out fixed the issue. The debris clogged up the filter, etc and impeded on fuel flow up high.

That being said, generally when I see this issue, it's either a bad pump or a fuel leak, generally in the tank.
 
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