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)
4500 pull (orange is rail pressure, green RPM, blue AFR)
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)
4500 pull (orange is rail pressure, green RPM, blue AFR)
Attachments
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