Mechanics

FUEL PRESSURE SPECS

2002 Ford Taurus

Engine Performance problem
2002 Ford Taurus 6 cyl Front Wheel Drive Automatic 161000 miles

My '02 Taurus has the 3.0L OHV engine. I have been experiencing a loss of power and " miss" at highway speeds since I've owned the vehicle. I own both the Ford shop manual and the Ford emission control and diagnostic manual. Both show different specs for my fuel pressure. The shop manual says 50-56 psi (350-380kpa). The emission diagnostic manual says 39-65 psi (270-450kpa), both koer. I've monitored the fuel pressure while driving with my scan tool and it stays near 270 kpa and fluctuates slightly over and below that number. Turning the A/C on is when the problem is most noticeable, and I don't see a rise in fuel pressure when I do. I'm thinking I should check the fuel pump driver module as I have already replaced the pump with another unit (used). Also, what spec should I look at?
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Jabrunn
August 23, 2010.



39-65 psi is the correct spec for the Pulse Width Modulated system.

Wrenchtech
Aug 23, 2010.
So what's the 50-56 psi spec for in the Ford shop manual? Alldata. Com lists both of these specs on their site for this car.

Tiny
Jabrunn
Aug 24, 2010.
The 55 to 60 spec is for a vehicle that doesn't have PWM fuel pressure.

I assume you did because you said you have a fuel pump driver module which is only used with PWM.

Wrenchtech
Aug 24, 2010.
So then is it normal for fuel pressure to stay at the bottom of the spec (270 kpa), fluctuating slightly up and down, thoughout the entire time you're driving? The fuel pressure stays steady on flat interstate, on hills, accelerating with the A/C on and off. Thanks for all your help.

Tiny
Jabrunn
Aug 24, 2010.
Yes, that's the whole theory of that system. It adjusts to load. It has a vacuum sensor that feeds the PCM and it combines that info with speed, gear ratio, TPS, coolant temp and air flow to make pressure decisions.

Wrenchtech
Aug 24, 2010.
Thanks for all your help. I have one more question regarding this. I installed another Fuel Pump Driver Module and the fuel pressure went up to around 400 kpa at idle. I checked the pressure again with my scanner today at idle and got the same results. I checked the pressure with a manual gauge at the same time and got around 60 psi. I decided to drive the car and the more I drove the more the pressure dropped. I'm baffled as I was sure the pressure would rise with load, as load increased while driving. I'm am just about at wits end on this. Thanks again.

Tiny
Jabrunn
Aug 28, 2010.
I think your forgetting temperature. It runs a richer mixture when the engine is cold so it wouldn't surprise me that the pressure drops with engine heat. I think your worrying about nothing here. The PCM is programmed to look for problems and will usually find them before you.

Wrenchtech
Aug 28, 2010.
As far as the fuel pressure is concerned, I'm sure you're right. I'm just baffled at what is causing the car lose power (like a gently buck at highway speeds) and miss. All ignition components were tested at a local dealer and passed. I'm going to put the vacuum pump I just purchased to use on Tuesday and begin checking for leaks. Thanks again. I really appreciate your help.

Tiny
Jabrunn
Aug 29, 2010.
I saw no mention of plugs, wires or coils in your history. Those would always be the first things to look at with symptoms like that. You should be able to use a scan tool on this and see the actual misfire counts for every cylinder.

Also make sure what your feeling isn't the TCC jumping in and out of overdrive. That can feel like a miss too.

Wrenchtech
Aug 29, 2010.
The plugs, wires and coil have been replaced. The original coil had a crack and was causing a misfire. I'm not seeing any info about misfires with my scan tool. It shows everything as ok. I am noticing that it records the results of the diagnostic tests it runs on the evap system as sometimes high or low. I'm going to check for vacuum leaks and take the vehicle to a transmission shop to make sure it's not the torque converter.

Tiny
Jabrunn
Aug 29, 2010.