Fuel Pressure Quandary

70SCJ

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After my tuner alerted me to a fuel pressure issue on a data log I find my self at a loss. The fuel pressure in the logs and on my aeroforce gauge show about base pressure 45psi and do not vary more that 1-2 psi in any driving condition. I have full return fuel system that has the adjustable regulator after the fuel rails. The car puts out about 16 lbs of boost. I have manually adjusted the fuel pressure on the regulator and I can adjust up or down. The vacuum/boost line is plugged into the factory sensor and teea off to the fuel pressure regulator and to the aeroforce boost sensor. I have attached a mechanical gauge to the fuel rail and can see the fuel pressure come up and down very close to a 1:1 with boost pressure. I have replaced the factory fuel sensor and still get the same readings as before. Could this be a wiring issue from the factory sensor to the PCM?
 

VNMOUS1

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After my tuner alerted me to a fuel pressure issue on a data log I find my self at a loss. The fuel pressure in the logs and on my aeroforce gauge show about base pressure 45psi and do not vary more that 1-2 psi in any driving condition. I have full return fuel system that has the adjustable regulator after the fuel rails. The car puts out about 16 lbs of boost. I have manually adjusted the fuel pressure on the regulator and I can adjust up or down. The vacuum/boost line is plugged into the factory sensor and teea off to the fuel pressure regulator and to the aeroforce boost sensor. I have attached a mechanical gauge to the fuel rail and can see the fuel pressure come up and down very close to a 1:1 with boost pressure. I have replaced the factory fuel sensor and still get the same readings as before. Could this be a wiring issue from the factory sensor to the PCM?
Are you running your boost reference line in front of your fuel rail pressure sensor? ie a T between the lower intake manifold and the rail?

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70SCJ

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Are you running your boost reference line in front of your fuel rail pressure sensor? ie a T between the lower intake manifold and the rail?

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Yes, that is correct.
 

serickson1

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Mine does the same thing and has for years.......Ngauge logs show 55psi throughout a WOT pass....my Autometer Colbalt gauge shows a 1:1 increase with boost....I haven't spent anytime finding out why.....if your A/F is money your good to go.
 

69b302

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Most people keep the FRPS and let it adjust the injectors, based on the pressure drop over the injectors. So the PCM will compensate for low fuel pressure, if you have injector left, even on a return system. I would not discount a low reading from the frps. What are the specifics of your return system?
 

70SCJ

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Most people keep the FRPS and let it adjust the injectors, based on the pressure drop over the injectors. So the PCM will compensate for low fuel pressure, if you have injector left, even on a return system. I would not discount a low reading from the frps. What are the specifics of your return system?
Full return system with 3x465 pumps. AN-10 from tank to rails where is splits to 2x AN-8's to the rails feeding ID1300's then both 8's route to the adjustable FPR then an AN-8 return. FRPS is out of the system.
 

69b302

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The systems sounds similar to mine, except I kept the FRPS. If the FRPS is out of the picture, the PCM would not have any boost referenced fuel pressure. What are they logging on the PCM that has them concerned?
 

70SCJ

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The systems sounds similar to mine, except I kept the FRPS. If the FRPS is out of the picture, the PCM would not have any boost referenced fuel pressure. What are they logging on the PCM that has them concerned?
Fuel rail pressure.
 

SCGallo2

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I have a theory that the Fuel Pressure PID you are monitoring and datalogging is Differential Fuel Pressure (pressure drop across the injectors). Differential Fuel Pressure = Actual Fuel Pressure – Relative Manifold Pressure (vacuum or boost in psi). Our setups are obviously different, but I believe our AeroForce gauges are reading the same PID due to similar model year. I have an OEM returnless fuel system with ID1000 fuel injectors for comparison. There may be a separate Fuel Rail Pressure PID or DMR in LiveLink that can be datalogged. I experimented with my car today to satisfy my curiosity. Here is what I found:

With Key On Engine Off, fuel rail pressure on the AutoMeter gauge matched the fuel pressure PID displayed on the AeroForce gauge at 42.3psi with zero manifold vacuum or boost: 42.3 psi – (0 psi) = 42.3 psi

Pic 1.jpg


With Key On Engine On at idle, fuel rail pressure on the AutoMeter gauge was roughly 28 psi and the fuel pressure PID displayed on the AeroForce gauge was 39.1 psi with (-10.1 psi) manifold vacuum: 28 psi – (-10.1 psi) = 38.1 psi. I cannot account for the 1 psi error, total gauge/sensor tolerance maybe???

Pic 2.jpg
 

70SCJ

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I have a theory that the Fuel Pressure PID you are monitoring and datalogging is Differential Fuel Pressure (pressure drop across the injectors). Differential Fuel Pressure = Actual Fuel Pressure – Relative Manifold Pressure (vacuum or boost in psi). Our setups are obviously different, but I believe our AeroForce gauges are reading the
QUOTE]
 
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70SCJ

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Actually, I’m monitoring both of those PIDs. The fuel rail pressure PID and my aero force gauge read the same. I wondering if taking the FRDM out of the system has caused the issue.
 

69b302

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I don’t think removing the FPDMs would cause bad readings from the FRPS. Do all the pumps run full time or a Hobbs switch on pumps 2 and 3? Assume filter and kinked lines have been checked. Does the pressure only drop on WOT, and about what rpm? Also, the pressure drop across the injector PID is what will be consistent at the pressure your regulator is set, and is what is actually programmed in the tune vs absolute rail pressure.
 
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70SCJ

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I don’t think removing the FPDMs would cause bad readings from the FRPS. Do all the pumps run full time or a Hobbs switch on pumps 2 and 3? Assume filter and kinked lines have been checked. Does the pressure only drop on WOT, and about what rpm? Also, the pressure drop across the injector PID is what will be consistent at the pressure your regulator is set, and is what is actually programmed in the tune vs absolute rail pressure.

All pumps (3) run full time.
At this point I don't think the pressure drops at WOT. I have put a mechanical gauge on the rail and have used an Endo camera to watch the pressure rise with a mashing of the throttle. I might try to rig up a camera and record a quick WOT run on a backroad. If I can't get that done I'll head back to a local dyno for a quick pull to check. I'll have to do that eventually anyhow so I can get my tuner a WOT log so he can finish up the tune.
 

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