Fuel system woes... Still dropping rail pressure w/new pumps

04GTMustang

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Hey guys… Sorry for the long post but I believe all this information below is necessary in diagnosing my issue:

I’m having a hell of a time trying to figure out what is wrong with my fuel system. I was at the dyno three weeks ago, made about 660 SAE which is about where the car usually is, however my tuner (Pete Johnson, a very skilled tuner) said he noticed my fuel rail pressure had dropped as low as 32 or 33 at the very top which was at 6000-6100 RPM. He suspected that my fuel pumps were getting “tired”, as they are five years old and on a return style system. My injector duty cycle was 74%.

This was my fuel set up:

-Fore Innovations Hat, 2x GSS 342 255lph pumps
-FC3 controller, 4ga wiring from distribution box
-Fore regulator attached to stock fuel rails
-8 feed / -8 return both stainless braided, inline 88mm fore filter
-80lb injectors

The car previously made 730 uncorrected/observed, this was about two years ago with ambient temperatures at about 20°F and a -3000 foot density altitude. I believe the fuel system that day was about tapped out, but that is a far cry from where I was a few weeks ago.

So, I sent my fore hat back to fore innovations, they tested and replaced the pumps (they said that they were not performing to specification) and installed:

- 1x GSS 342 G3 (255 lph)
- 1x GSS 352 G3 (340 lph, but they stated their independent testing shows 15%+ more flow over advertised by Walbro).

Got everything back and took it for a drive. I data logged my recent drive, logging fuel rail pressure, RPM, and air fuel ratio (showing as analog). I have attached both of these files along with a screenshot if you don’t have Livelink on your computer.

Basically, I am seeing the fuel pressure start to drop again as early as 4600 RPM. At cruise, I am seeing 40 to 40.5 psi of fuel pressure. At the hit, it drops to 39 psi and holds there until 4600 RPM, and then continues to drop off slowly. Right at the end of the pull right near 6000 RPM, fuel pressure was as low as 33.3 psi, and the wideband can be observed starting to creep up at the very end. Even on the half pull I also attached, its dropping to 38.x at 4500 rpm where I let off.

I am completely out of ideas what could be causing this. Brand-new pumps with one being a 340 lph, -8 feed braided so they can’t “kink”, I have a 160 amp ebay alternator with the big 3 wiring upgrade, and I have a gauge in the car that shows volts. I’m never under 13v at the top of a pull. It’s usually closer to 13.6 however when you data logged of voltage it drops to as low as 12.8 (although it reads as much as ½ a volt lower at the PCM). So that rules out power to the pumps (I think), the new pumps themselves, the injectors, the -8 lines, etc.

Am I overlooking anything? Does anybody have any ideas why this is happening? For some reason, the fuel system in this car has never been up to par even when it was stock with a boost-a-pump. I barely had enough fuel with the stock system with a 2.93 pulley prior to the boost-a-pump too. Probably unrelated, but I figured I would add it in.

Once again, sorry for the long post.

TLDR: fuel rail pressure dropped as low as 32 psi when I was at the dyno a few weeks ago. Replaced and got larger fuel pumps, issue did not resolve.

6000rpm pull (orange is rail pressure, green RPM, blue AFR)
upload_2020-9-27_19-39-29.png


4500 pull (orange is rail pressure, green RPM, blue AFR)
upload_2020-9-27_19-45-1.png
 

Attachments

  • 6000rpm_pull.csv
    523.6 KB · Views: 30
  • half_pull.csv
    335.9 KB · Views: 34
  • upload_2020-9-27_19-39-37.png
    upload_2020-9-27_19-39-37.png
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RainyP71

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I would check for damage and measure resistance on all wiring to fuel pumps and any other controllers you have to 100% rule out an electrical issue and then start working from there if all looks well. Interesting problem....

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04GTMustang

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I would check for damage and measure resistance on all wiring to fuel pumps and any other controllers you have to 100% rule out an electrical issue and then start working from there if all looks well. Interesting problem....

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Thanks for the reply. I think that's a reasonable assumption, I'm leaning towards electrical as well, due to the other components not being near limitations. I was thinking the fuel filter being a culprit, but it's only been like 6000 miles since I installed that beefy 88mm fore unit. I can't imagine that's a cause. I also thought maybe the metal line at the stock fuel rail could be kinked or bent, but then again, it made 730 before and nothing under the hood has changed. And the line looks normal...


I measured 13.9v at the FC3 controller in the trunk while idling. I was 14.1v at the battery during this. So a 0.2v loss at the controller. My power comes from a 4ga wire connected to the dist box.

Another thing worth noting: my inertia switch is backwards. Has been ever since this return fuel system. Only runs when the button is "popped". When I reset it and push it in, it disconnects power to the FC3 and the car immediately stalls (with fuel still in the line). Why the f*** is this? Bad inertia switch or did I fook the wiring on this (to my defense, a friend was helping me with this part and he did this section). I can't imagine this as a cause, but I'm confused.

Edit: This is a newb electrical question, but how would I measure the resistance of the fuel controller power wire if the ends of the wire are on opposite ends of the car? Could I just measure the pos and neg wire together to see resistance through the entire circuit?
 
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01yellercobra

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Is there a way to check the regulator? Maybe it's bleeding pressure at the top end.

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04GTMustang

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Is there a way to check the regulator? Maybe it's bleeding pressure at the top end.

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That's a good question. IDK how, but fore may know. I can email them to get their input.

However, how would the regulator know it's at the "top" end? Isn't it just responsible for maintaining a certain pressure regardless of everything else? In other words, do you think it would bleed pressure under boost at any RPM if this was the issue versus just at the top?
 

SVT GI

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Sounds like the controller got wired into the wrong side of the inertia switch.

Looking at the logs it doesn’t look like the rail pressure goes up at all. Look at the boost reference line on the regulator. If the line is bad or leaking under boost it won’t keep up with the 1:1 demand. Even if pumps are weak or having voltage drop issues, you should be making some boost at the hit and that should increase even at lower rpms but I’m not seeing it.
 

01yellercobra

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That's a good question. IDK how, but fore may know. I can email them to get their input.

However, how would the regulator know it's at the "top" end? Isn't it just responsible for maintaining a certain pressure regardless of everything else? In other words, do you think it would bleed pressure under boost at any RPM if this was the issue versus just at the top?
It's supposed to increase fuel pressure with boost pressure. As mentioned in the other post for every 1psi of boost increase you should see 1psi of fuel pressure increase. So while at idle you'll see 40psi under boost you'll see 70psi. Otherwise the fuel pressure won't be able to overcome the boost pressure in the intake.
 

04GTMustang

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Sounds like the controller got wired into the wrong side of the inertia switch.

Looking at the logs it doesn’t look like the rail pressure goes up at all. Look at the boost reference line on the regulator. If the line is bad or leaking under boost it won’t keep up with the 1:1 demand. Even if pumps are weak or having voltage drop issues, you should be making some boost at the hit and that should increase even at lower rpms but I’m not seeing it.

So this is logged with the PID "Pressure drop across injectors" which I believe is always supposed to show 39 psi, which it does at WOT (initially). I have a gauge in the car that measures FRP with a 1/8 NPT port right on the rail on the passenger side, and that does go up when you get into boost. I will take a look at that line regardless.

It's supposed to increase fuel pressure with boost pressure. As mentioned in the other post for every 1psi of boost increase you should see 1psi of fuel pressure increase. So while at idle you'll see 40psi under boost you'll see 70psi. Otherwise the fuel pressure won't be able to overcome the boost pressure in the intake.

My 1/8 NPT sensor reads 50 psi at idle which is attached directly to the rail (and has no influence from a VAC line). It goes up with boost, that 39 psi I'm seeing on the log is from "pressure drop across injectors" which is supposed to read 39 psi all the time AFAIK.
 

04GTMustang

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I FIGURED IT OUT!

For ALL of these years, I never had a jumper between the Remote 1 and Remote 2 ports on the FC3 controller. I never thought this could be a cause as I've made as much as 700+ before on ONE GSS 342!!!

I haven't driven the car yet, but I can definitely hear both pumps screaming now and my base fuel pressure is WAY higher.
 

RainyP71

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I FIGURED IT OUT!

For ALL of these years, I never had a jumper between the Remote 1 and Remote 2 ports on the FC3 controller. I never thought this could be a cause as I've made as much as 700+ before on ONE GSS 342!!!

I haven't driven the car yet, but I can definitely hear both pumps screaming now and my base fuel pressure is WAY higher.
Man that's badass, CONGRATS! Post those new numbers!!!!!

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01yellercobra

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I FIGURED IT OUT!

For ALL of these years, I never had a jumper between the Remote 1 and Remote 2 ports on the FC3 controller. I never thought this could be a cause as I've made as much as 700+ before on ONE GSS 342!!!

I haven't driven the car yet, but I can definitely hear both pumps screaming now and my base fuel pressure is WAY higher.
How hard did you slap your forehead when you figured it out?
 

gtmustang00

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Glad you got it figured out. I am in the middle of my Fore install and will make sure the jumper wire is there.
 

04GTMustang

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Man that's badass, CONGRATS! Post those new numbers!!!!!

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Will do! So relieved...

Nice find! Love it when it's a simple find.

Same here. Albeit frustrating, considering I just spent another $250 on new pumps for no reason, but I guess it's a good refresh to do and gives me even more capacity. Hopefully my alternator holds...

How hard did you slap your forehead when you figured it out?

I wanted to throw myself down the stairs a few times so dumb! Next time I'll make sure to RTFM.

Glad you got it figured out. I am in the middle of my Fore install and will make sure the jumper wire is there.

I spoke with Justin, he said if you plan on running full time for both pumps, run them off the pump two and pump three ports. Then just run a single 12 volt signal from your inertia switch to the remote two as that remote runs pump two and three. That eliminates the need for a jumper. He recommended strongly to stage the second pump especially if it is a larger pump. I'm going to grab that Honeywell for PSI pressure switch and put my larger 350 walbro on a stage setup. Good luck!
 

gtmustang00

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Will do! So relieved...



Same here. Albeit frustrating, considering I just spent another $250 on new pumps for no reason, but I guess it's a good refresh to do and gives me even more capacity. Hopefully my alternator holds...



I wanted to throw myself down the stairs a few times so dumb! Next time I'll make sure to RTFM.



I spoke with Justin, he said if you plan on running full time for both pumps, run them off the pump two and pump three ports. Then just run a single 12 volt signal from your inertia switch to the remote two as that remote runs pump two and three. That eliminates the need for a jumper. He recommended strongly to stage the second pump especially if it is a larger pump. I'm going to grab that Honeywell for PSI pressure switch and put my larger 350 walbro on a stage setup. Good luck!

Yes I have 2 485 pumps. Will run one full time and the 2nd on a Hobbs switch. Just trying to figure out where in the passenger fender well to mount the regulator. Pete's a good guy. Been using him since the car was new in 2003.
 

04GTMustang

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When you figured it out you probably felt like Edison watching a bulb light up for the first time lol.

It was a combination of that and "I can't believe I've been driving on 1 pump for 4 damn years".

Yes I have 2 485 pumps. Will run one full time and the 2nd on a Hobbs switch. Just trying to figure out where in the passenger fender well to mount the regulator. Pete's a good guy. Been using him since the car was new in 2003.

I just ordered my Hobbs switch. Justin sent me a PDF file of how they recommend wiring it. Basically solder one of the wires from the Hobbs to your 12-volt power wire for your primary remote one pump and use the second wire into the remote two location. This way you don't have to create an additional tap into a switched to 12 volt source, you are just piggybacking off off the primary pump trigger if that makes sense...

I think I'm going to tee off mine in the glove box where I have my boost line for the stock gauge and my aftermarket boost gauge.
 

04GTMustang

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Also, how are you guys running your primary remote pump power? Mine is off the inertia switch. As I described earlier, my inertia switch works in reverse so if you push the button to reset it the car shuts off and if you whack it with a hammer and pop it, everything runs. I want to fix this, I wasn't the initial person to wire this...

I think the wire for my pump power comes off the white wire on the inertia switch. How are you guys running it? I don't have my FPDM anymore so I'm guessing I could use one of those wires instead of the inertia switch or switch to using one of the FPDM power wires? I don't think I'll be able to retain the factory/OEM priming functionality without the FPDM but I'm okay with my pumps running full time if my inertia switch is working correctly.
 

01yellercobra

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Have you checked out the switch. Sounds like something is funky inside it. An open switch should kill power no matter what.

That being said I have the power from the switch triggering the relays. I don't remember the colors though. It's been a while since I've looked back there.
 

04GTMustang

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Have you checked out the switch. Sounds like something is funky inside it. An open switch should kill power no matter what.

That being said I have the power from the switch triggering the relays. I don't remember the colors though. It's been a while since I've looked back there.

That's what I was thinking, how on earth could that switch run power through it if it is popped? Something must be wired backwards or the switch is bad.

I'm not sure how I would go about testing the switch. I could run a resistance/ohms test on it somehow but I'm just not that savvy with electrical stuff.

if you happen to go back and look at it do you mind snapping a picture or anyone who has access to theirs without having to rip apart their interior too much?

It seems too much of a coincidence that the switch would have gone bad the day I wired in the return style system unless something got shorted while doing it and somehow it's operating in reverse? I have no clue...
 

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