Hi all. First post here. I have a 2003 cobra. I installed a 2.3 whipple, 60 lb injectors, maf. Car was previously tuned with a chip which I had removed. Using an sct tuner to get tuned. Tuner said he had to add a bunch of fuel to the base tune. (Very reputable tuner). Decided to check fuel pressure at the rail. 14psi. Makes alot of sense as to why he had to add so much fuel. I drove the car for 2 years without issue. I check fuel rail pressure pid using laptop and sct x4. Fuel pressure reads 38-40. Exactly what it is supposed to be. At the moment I'm confused and not sure where to start checking. Idles at 14-15 afr. Any help would be greatly appreciated. What to get this thing running properly asap
03 Cobra Low Fuel Pressure
- Thread starter CTsnake_03
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So, you're getting a different reading from the mechanical gauge at the rail vs. what you're seeing in the SCT?
Correct. I used two seperate fuel pressure gauges and both read 14psi. The datalog shows 38-40psi read from frps. Exactly the spec. Im a tech but not too familiar with this fuel system.
Ok, thoughts:
The mechanical pressure gauge [could] be bad. Did you remove the valve stem from the rail when you hooked it up?
Next:
The original tune may have had an offset for the fuel pressure sensor. If this is true, then the same offset needs to be included in the SCT tune. If not, then I would say that the sensor is bad.
You're dealing with a returnless fuel system. So, if the sensor reports that fuel pressure is [good] then it will reduce demand to the pump if the sensor is reading high and reduce the pump to what it thinks is appropriate.
If the FRPS is wrong OR the tune scaling is wrong, the system will actively cause low fuel pressure
FRPS = Fuel Rail Pressure Sensor
The mechanical pressure gauge [could] be bad. Did you remove the valve stem from the rail when you hooked it up?
Next:
The original tune may have had an offset for the fuel pressure sensor. If this is true, then the same offset needs to be included in the SCT tune. If not, then I would say that the sensor is bad.
You're dealing with a returnless fuel system. So, if the sensor reports that fuel pressure is [good] then it will reduce demand to the pump if the sensor is reading high and reduce the pump to what it thinks is appropriate.
If the FRPS is wrong OR the tune scaling is wrong, the system will actively cause low fuel pressure
FRPS = Fuel Rail Pressure Sensor
Thats what im thinking. I replaced fuel filter, fuel pumps, frps, fpdm. No change. Checked the voltage going to the fpdm and 14v. Checked voltage at pump connector. 14v. 3.5v voltage drop across the pump.as it idles. Everything is checking out ok. Dont know what else I can do on my end. I hooked up the boost a pump as the instructions directed and got 80psi at idle. Disconnected again.
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