no fuel pressure 97 taurus

car quit. no fuel pressure. my tester indicated power at fuel pump wires but later i discovered it would go away when fuel pump was connected so it was a false reading. So i mistakenly dropped the tank and removed fuel pump. Discovered it worked fine when hooked to battery. located and removed ccrm (relay module which powers fuel pump) and found it to be good and not receiving turn on ground from the computer (pcm). cut the pcm feed to the ccrm,wired a switch to switch ground and turn on fuel pump. reassembled vehicle. runs fine. I probably spent 12 hrs on line reading auto forums and chasing wiring diagrams and less than 5 hrs actually working on car. thanks for all the help.

Thanks for the tip. I'm going to ask for some clarification as to what you think the problem was. Are you saying that the ground for the CCRM to control the fuel pump relay was not good? Did you wire in then just a manual switch to enable the fuel pump relay in the CCRM? Do you plan to continue checking the wiring to determine where the corroded connection exists? It sounds like corrosion since you measured voltage when the circuit was not loaded. Although that was at the fuel pump rather than input to the CCRM if I interpreted what you typed correctly.

During normal operation the PCM will only energize the fuel pump for the first few seconds after turning the key to the Run/Start position to prime the fuel system. Maybe that's why you measured voltage once and not the next time. Until the car is running, the fuel pump will not be energized continuously. That makes it a bit difficult to trace wiring for the fuel pump circuit if the car doesn't start and run.

-Rod

Rod , I was under the impression the fuel pump ran continuosly and pressure regulation was taken care of up front. I figured the pcm just was inoperative on the part that turns on ccrm relay. corrosion or burned out circuit was my guess. All connectors were dry, shiny and sealed well . Does the computer monitor fuel pressure and cycle the fuel pump accordingly. this is the 2v 3.0 L vulcan. We have been driving it for a week. gas mileage is normal. We've been thru a tank of gas. How does the computer monitor fuel pressure. Thanks alot. I thought I was done and was happy cuz I didn't have to buy any parts. appreciate the help.

Nope, according to the factory service manual for your 1997 Taurus (note the bold sections below):

"The fuel system has a fuel pump relay (part of constant control relay module [CCRM]) controlled by the powertrain control module (PCM) (12A650), which provides power to the fuel pump under various operating conditions.

" When the ignition switch is in the OFF position the powertrain control module and fuel pump relays are not energized.

" When the ignition switch is first turned to the RUN position:

"-- The PCM power relay is energized.

"-- Power is provided to both the fuel pump relay and to a timing device in the powertrain control module.

"-- The fuel pump is supplied power by the fuel pump relay.

" If the ignition switch is not turned to the START position the timing device in the powertrain control module will open the ground Circuit 57 (BK) (after approximately one second). Opening the ground circuit de-energizes the fuel pump relay, which in turn de-energizes the fuel pump. This circuitry provides for pre-pressurization of the fuel system.

" When the ignition switch is turned to the START position the powertrain control module operates the fuel pump relay to provide fuel for starting the engine while cranking.

" After the engine starts and the ignition switch is returned to the RUN position:

"-- Power to the fuel pump is again supplied through the fuel pump relay.

"-- The powertrain control module senses engine speed and shuts off the fuel pump by opening the ground circuit to the fuel pump relay when the engine stops or is below 120 rpm."


Some of the newer Fords use a returnless system with a fuel pressure sensor to regulate fuel pressure. The PCM uses the sensor readings to provide a pulse-width modulated (PWM) signal to the fuel pump. However, your 1997 Taurus uses a less sophisticated fuel pressure regulator and returns excess fuel to the tank. The regulator has fuel pressure on one side of a spring-loaded diaphragm and balances that against manifold vacuum to maintain a constant pressure drop across the injectors.

-Rod