[jaba]

I have a 2002 Taurus with the 3.0L OHV engine. This car uses the electronic returnless fuel system. I have been having a driveability concern with the vehicle for over a year now.
At highway speeds the car feels like it loses power and misses. I have replaced the plugs, wires, coil, both upstream O2 sensors, PCV valve and hoses. I have cleaned the MAF sensor and back probed the TP sensor to see if voltage rises steadily and smoothly with throttle movement and it did.
I replaced the fuel pump driver module having noticed that the fuel pressure was staying at the bottom of the spec (270 kpa) while driving at highway speeds (with or without the A/C on). The idle pressure immediately rose to about 411 kpa. I checked the pressure with a manual gauge got a reading of around 60 psi. It used to be around 32 psi. Now as I begin to drive, with an increase in speed, the fuel pressure begins to drop. The faster I go the lower the pressure.
I checked the resistance on the Fuel Rail Pressure Sensor using the specs in Ford's Emission Control Diagnostic manual and the resistance on mine is high.
Anyone have anything similar to this. This problem has baffled me and everyone I have presented it to and even the dealerships are unable to help after running diagnostics on the vehicle. I would appreciate any comments or suggestions. Thanks.

 

[brooksbronco17]

What about the fuel filter? I assume the 02 has one. Bet you replaced it but forgot it in your list. Could the fuel pump itself be getting lazy and on it's last legs?

 

[jaba]

What about the fuel filter? I assume the 02 has one. Bet you replaced it but forgot it in your list. Could the fuel pump itself be getting lazy and on it's last legs?

Yeah, actually I did forget that. I replaced the fuel filter with a new one and replaced the fuel pump with a used one. Before putting the used pump in I replaced both mesh socks with new ones. There was virtually no change in fuel pressure after doing these things.

I'm leaning toward a vacuum leak somewhere but just not completely sure. I've been searching for the cause of this issue for some time now, well over a year. I have had the car checked at two local dealerships and have no definitive answers. I know I'll find it eventually but I want it to be before I'm in a nursing home lol.

Thanks for the reply and if you have any other suggestions, I'm all ears (or eyes in this case).

 

[jaba]

I found the reason for the "crazy" fuel pressure readings. I found my answer on www.d-tips.com. It's a great website with it's information avalable by subscription only but it's worth it.

The times I noticed the fuel pressure the highest were when the engine was hot, after it had been run a while. When the PCM senses hot fuel in the rail, it raises the fuel pressure to keep the fuel in the rail from vaporizing, hence, the high fuel pressure. The fuel rail pressure sensor mounted to the rail on bulls equiped with the electronic returnless fuel system also has a fuel temp sensor inside (which I never knew).

So, if you're ever checking your fuel pressure and, gasp!, it's way to high, ask yourself this - is the engine hot because you've just driven the car enough to completely warm everything up? If so, then most likely it's your pcm compensating for the high temps in the fuel rail.

Btw, I'm not being paid (or compensated in any other way for that matter) to give word-of-mouth advertising for d-tips.com but I am impressed the the information I found there, especially on Mode$6 data that my scan tool was recording (but might as well have been displayed in Greek).