5.0 fuel pressure

[shadowless127]

Can one or two misfiring cylinders cause the fuel pressure from the schrader valve to drop when you get on throttle?

 

[imp]

Can one or two misfiring cylinders cause the fuel pressure from the schrader valve to drop when you get on throttle?

No. Fuel pressure is regulated to remain in a fairly tight range, only a couple of psi from idle to wide open throttle. If it did not, fuel trim could not be maintained.

How are you determining this? Gauge connected to Schrader, engine idling, then opening throttle? If pressure drops doing that, look for failed pressure regulator, clogged fuel filter, failing fuel pump. imp

 

[shadowless127]

No. Fuel pressure is regulated to remain in a fairly tight range, only a couple of psi from idle to wide open throttle. If it did not, fuel trim could not be maintained.

How are you determining this? Gauge connected to Schrader, engine idling, then opening throttle? If pressure drops doing that, look for failed pressure regulator, clogged fuel filter, failing fuel pump. imp

Mechanic said he hooked up a fuel pressure gauge and when he got on the throttle the fuel pressure dropped. He didn't test the regulator, the fuel filter is 2 months old, pump is the original. He claims that my fuel pressure is dropping because of the misfires, which I personally thought was bullshit especially since I have 2 lean codes, and the misses started at the same time I got the lean codes. That to me points to a fuel delivery problem.

 

[2000StreetRod]

misfire cause

It's more likely that the low fuel pressure is causing the misfires than vice versa. I suggest that you find another mechanic. The fuel pressure regulator on your 2001 is located in the fuel tank. The component on the fuel rail is the fuel pressure damper. Unless your fuel pump has been replaced it is 14 years old. The brushes in the pump are probably no longer making reliable contact. I suggest purchasing something other than an Airtex replacement pump. Many members have experienced poor reliability with that brand.

 

[imp]

Mechanic said he hooked up a fuel pressure gauge and when he got on the throttle the fuel pressure dropped. He didn't test the regulator, the fuel filter is 2 months old, pump is the original. He claims that my fuel pressure is dropping because of the misfires, which I personally thought was bullshit.

It is bullshit. Picture what's happening, whether or not mis-fire occurs: injectors are dumping fuel into all cylinders, good ones and misfiring ones. Misfire creates lots of unburned hydrocarbons, probably ups the carbon monoxide, too. O2 sensors "see" that, inform the computer, which then determines which bank is running too rich and "throws" a trouble code. It can't determine closer than that: there are 3 or 4 cylinders in each bank, V-6 or V-8. If misfiring, up to the mechanic to find which cylinder it is, whether ignition, or injector problem.

But fuel pressure related to misfire? I don't see how. A slug of dirty gas bought since filter was replaced could easily be the culprit IF pressure is indeed dropping. I assume you have not seen that with your own eyes.

If this is a "returnless" fuel system, it likely has a Fuel Pressure and Temperature sensor, which tells the computer what the fuel pressure actually is at all times. As demand for fuel changes, the pump speed is constantly varied to maintain pressure within limits. The computer can only "see" a bad Fuel Pressure and Temperature Sensor if it's electrical characteristics go haywire; it contains a mechanical diaphragm, connected to engine vacuum . A fuel leak there would be sucked into the engine and burned as excess fuel, but all the computer would know is that too rich running has occurred.

The older "return-type" fuel system has the "excess" fuel delivered to the fuel rail diverted back to the tank by the Fuel Pressure Regulator mounted on the rail, also a diaphragm operated valve, but has no electrical connection to the computer, so knowledge of it's functioning is limited to looking at exhaust quality via O2 sensors. I don't recall offhand which system your engine would have. If there are two tubes running to the fuel rail, it is return-type. They are usually close together.

That's the theory of it, more or less. You would really need more detailed info on exactly what is going on. What "testing" was done, confirm what trouble codes are present. More explicit, I might be able to help. imp

 

[shadowless127]

It's more likely that the low fuel pressure is causing the misfires than vice versa. I suggest that you find another mechanic. The fuel pressure regulator on your 2001 is located in the fuel tank. The component on the fuel rail is the fuel pressure damper. Unless your fuel pump has been replaced it is 14 years old. The brushes in the pump are probably no longer making reliable contact. I suggest purchasing something other than an Airtex replacement pump. Many members have experienced poor reliability with that brand.

That was my guess since I also have a p0171 and p0174 (Everyone should own their own OBDII scanner).

The Airtex is a universal pump isn't it? I didn't remember seeing any vendors selling a full airtex assembly.

It is bullshit. Picture what's happening, whether or not mis-fire occurs: injectors are dumping fuel into all cylinders, good ones and misfiring ones. Misfire creates lots of unburned hydrocarbons, probably ups the carbon monoxide, too. O2 sensors "see" that, inform the computer, which then determines which bank is running too rich and "throws" a trouble code. It can't determine closer than that: there are 3 or 4 cylinders in each bank, V-6 or V-8. If misfiring, up to the mechanic to find which cylinder it is, whether ignition, or injector problem.

But fuel pressure related to misfire? I don't see how. A slug of dirty gas bought since filter was replaced could easily be the culprit IF pressure is indeed dropping. I assume you have not seen that with your own eyes.

If this is a "returnless" fuel system, it likely has a Fuel Pressure and Temperature sensor, which tells the computer what the fuel pressure actually is at all times. As demand for fuel changes, the pump speed is constantly varied to maintain pressure within limits. The computer can only "see" a bad Fuel Pressure and Temperature Sensor if it's electrical characteristics go haywire; it contains a mechanical diaphragm, connected to engine vacuum . A fuel leak there would be sucked into the engine and burned as excess fuel, but all the computer would know is that too rich running has occurred.

The older "return-type" fuel system has the "excess" fuel delivered to the fuel rail diverted back to the tank by the Fuel Pressure Regulator mounted on the rail, also a diaphragm operated valve, but has no electrical connection to the computer, so knowledge of it's functioning is limited to looking at exhaust quality via O2 sensors. I don't recall offhand which system your engine would have. If there are two tubes running to the fuel rail, it is return-type. They are usually close together.

That's the theory of it, more or less. You would really need more detailed info on exactly what is going on. What "testing" was done, confirm what trouble codes are present. More explicit, I might be able to help. imp

Cool, that's what I thought.

Prior to bringing the car in I had a p0171, p0174, p0303, p0455. Apparently sometime between me dropping it off and the next day it threw a p0304 too.

I just need this vehicle to last me another 2-3 months and I'm done with it.

 

[2000StreetRod]

pressure & temperature sensors

. . . If this is a "returnless" fuel system, it likely has a Fuel Pressure and Temperature sensor, which tells the computer what the fuel pressure actually is at all times. As demand for fuel changes, the pump speed is constantly varied to maintain pressure within limits. The computer can only "see" a bad Fuel Pressure and Temperature Sensor if it's electrical characteristics go haywire; it contains a mechanical diaphragm, connected to engine vacuum . A fuel leak there would be sucked into the engine and burned as excess fuel, but all the computer would know is that too rich running has occurred.

The older "return-type" fuel system has the "excess" fuel delivered to the fuel rail diverted back to the tank by the Fuel Pressure Regulator mounted on the rail, also a diaphragm operated valve, but has no electrical connection to the computer, so knowledge of it's functioning is limited to looking at exhaust quality via O2 sensors. I don't recall offhand which system your engine would have. If there are two tubes running to the fuel rail, it is return-type. They are usually close together. . .

The 2001 has a returnless (only one line to the fuel rail) fuel system with a fuel pressure regulator located in the tank that allows excess fuel to flow to the tank. The fuel pressure/temperature sensor was not incorporated until the 2004 and later models that allowed the PCM to control the fuel pump speed (and pressure) via a pulse width modulator. The fuel pressure/temperature sensor has no diaphragm but electrically acts as if it does.

 

[shadowless127]

The 2001 has a returnless (only one line to the fuel rail) fuel system with a fuel pressure regulator located in the tank that allows excess fuel to flow to the tank. The fuel pressure/temperature sensor was not incorporated until the 2004 and later models that allowed the PCM to control the fuel pump speed (and pressure) via a pulse width modulator. The fuel pressure/temperature sensor has no diaphragm but electrically acts as if it does.

Those were incorporated due to the switch to drive by wire, which debuted in 2004.

 

[imp]

Yes, I knew the first returnless did not vary pump speed, but wasn't sure when the new pressure/temperature sensor was added. A vacuum hose definitely connects to it as I recall. If not a diaphragm, the vacuum must act upon a mechanically-moving part, to effect an electrical signal-change, right? imp

 

[2000StreetRod]

silicon diaphragm

I was wrong. Technically, it is a diaphragm but not one like those used in the traditional fuel pressure regulator. According to Bosch that makes the sensor for Ford:

"The piezoresistive pressure-sensor element and appropriate signal amplification and temperature compensation electronics are integrated on a silicon chip. The pressure measured acts on the back of the silicon diaphragm. The reference pressure acts from above on the active side of the silicon diaphragm. Thanks to the coating process employed, both sides are resistant to the gases and liquids occurring in the intake manifold."

I used one when I installed my electronic fuel pump controller in my 2000 Sport.

 

[koda2000]

Fuel pump wise, I've installed 4 Bosch 69128 fuel pumps this year and have one more I will be doing soon. I've had great success with the Bosch pumps. Airtex pumps are junk. The first pump I installed was an Airtex and it didn't even last 2 years (and under 12K).

If there's a question regarding your FPR you should probably get a complete assembly, but I don't know if Bosch offers one. Delphi or Motorcraft would be my suggestions for a complete assembly.

 

[shadowless127]

Fuel pump wise, I've installed 4 Bosch 69128 fuel pumps this year and have one more I will be doing soon. I've had great success with the Bosch pumps. Airtex pumps are junk. The first pump I installed was an Airtex and it didn't even last 2 years (and under 12K).

If there's a question regarding your FPR you should probably get a complete assembly, but I don't know if Bosch offers one. Delphi or Motorcraft would be my suggestions for a complete assembly.

At this point I'd just replace the entire assembly. If I'm paying to have the tank dropped i'd rather just replace everything at once.

 

[koda2000]

Your problem might be that there's a split or a leak in the short piece of fuel line between the pump and the FPR. I understand you wanting to replace the whole assembly and I'm not trying to talk you out of it, but it would be interesting to see if that's the case. It's been known to occur.

 

[shadowless127]

Your problem might be that there's a split or a leak in the short piece of fuel line between the pump and the FPR. I understand you wanting to replace the whole assembly and I'm not trying to talk you out of it, but it would be interesting to see if that's the case. It's been known to occur.

Like I said, I'm paying to have the tank dropped once; everything gets replaced lol.

Just called the mechanic and said i cant justify the bill he gave me for that truck. Miraculously he's not charging me a diagnostic fee, which is nice, so I won't lose that.

 

[shadowless127]

Ordered a Spectra Premium full hanger assembly from amazon for $122 shipped; will be here tomorrow.

FYI Airtex sells the same pump under 3-4 different brands. They all have the same part number.