Mechanics

FUEL PRESSURE ISSUE

1998 Ford Taurus

Engine Performance problem
1998 Ford Taurus 6 cyl Front Wheel Drive Automatic 110000 miles

At cold start the fuel pressure was 10 lbs (key on, no engine running). After starting engine fuel presure came up to 32 lbs very quick. Restarts the fuel pressure remained high. After waiting for a long period the fuel pressure would go back to zero and a step of turning key on and off ( not engine start) 3 or 4 times would bring the fuel pressure up to 40 lbs. Why is it taking so long for fuel pressure to come up. The initial 2 seconds of fuel pump before start does not seem long enough to bring pressure up to running pressure. Is this normal!
I kow it is not the fuel filter as I just replaced it, fuel pressure was to zero and it took 4 key (on and off) cycles to bring pressure up to 40 lbs. The normal 2 seconds doe not bring up the fuel pressure enough to start car efficently.
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Zue
October 2, 2010.




I need you engine size to look up specs, 3.0? 3.0 DOHC?
Flex fuel? Or 3.4?
With the Key on engine off reading should be 30-45 psi and test the system like this: 4) Check Fuel Pressure Release fuel system pressure. Turn ignition off. Install fuel pressure gauge. Turn ignition on. Using scan tool, access OUTPUT TEST MODE. Command fuel pump on. Note fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 10). 5) Check System Ability To Hold Fuel Pressure With fuel pressure gauge installed, turn ignition off. Exit OUTPUT TEST MODE. If fuel pressure remains within 5 psi (34 kPa) of specification for 60 seconds, go to step 7). If fuel pressure does not remain within 5 psi (34 kPa) of specification for 60 seconds, go to next step. 6) Check Pressure Regulator Diaphragm With fuel pressure gauge installed, start engine and operate for 10 seconds. Turn ignition off and wait 10 seconds. Start engine again and allow to idle for 10 seconds. Turn ignition off. Disconnect and inspect hose from fuel pressure regulator. If hose is wet with fuel, replace fuel pressure regulator. If hose is dry, go to step 12). 7) Check Fuel Pressure; Test Drive Vehicle With fuel pressure gauge installed, disconnect and plug fuel pressure regulator hose. Ensure fuel pressure gauge can be seen by vehicle operator. Drive vehicle while noting gauge reading during heavy acceleration. If fuel pressure reading stays within 3 psi (21 kPa) of original pressure reading, go to next step. If fuel gauge reading does not stay within 3 psi (21 kPa) of original pressure reading, go to step 13). 8) Check Fuel Pressure Regulator; Test Drive Vehicle With fuel pressure gauge installed, reconnect fuel pressure regulator hose. Install vacuum gauge to intake manifold. Ensure both gauges can be seen by vehicle operator. Drive vehicle while noting gauges during heavy acceleration. Gauge readings should be as follows:  Fuel pressure gauge reading increases and vacuum gauge reading decreases.  Fuel pressure gauge reading decreases and vacuum gauge reading increases. If gauge readings are as specified, fuel system is functioning properly and testing is complete. If gauge readings are not as specified, go to next step. 9) Check Vacuum Supply Turn ignition off. Disconnect and plug fuel pressure regulator hose. Install vacuum pump to fuel pressure regulator. Start engine and operate at idle. Observe fuel pressure gauge while applying vacuum to regulator. If fuel pressure changes as vacuum changes, repair restricted vacuum source. If fuel pressure does not change as vacuum changes, replace fuel pressure regulator. 10) Check Fuel Pressure Regulator Leave ignition off and scan tool connected to DLC. Release fuel system pressure. Disconnect fuel return hose at fuel rail. Connect a separate hose to fuel rail and put opposite end of hose in clean, one quart container. Turn ignition on. Enter OUTPUT TEST MODE. Command fuel pump on. Note fuel pressure and fuel returning to container. Exit OUTPUT TEST MODE. Command fuel pump off. If fuel pressure is 35-40 psi (240-280 kPa) 35-40 psi with fuel returning to container, go to next step. If fuel pressure is not 35-40 psi (240-280 kPa) or fuel is not returning to container, replace fuel pressure regulator. 11) Check Fuel Return Ensure fuel return line is disconnected at fuel rail. Disconnect fuel return hose at fuel pump. Check return hose for restrictions. Apply 3-5 psi (21-34 kPa) compressed air to return hose. If air flows freely, replace fuel pump. If air does not flow freely, repair or replace fuel return hose.
If there is any gas in the vacuum line to the regulator, replace the regulator.

Merlin2021
Oct 2, 2010.
I did all the checks but it seems that all numbers are good so far with exception of Cold Start pressure (engine off) being only 10 lbs. If I cycle key 4 time the pressure comes up to 40 lbs. Vacuum working. Vacuum fuel pressure regulator working. Leak down test OK, waited 5 minites and no pressure loss detected. Pinced return line and pressure increased to 60 psi. Vacuum is -18 lbs. Fuel filter new.

Tiny
Zue
Oct 2, 2010.
It sounds like the pump itself is getting tired. Takes too long to get up to initial pressure specs. Or the filter is clogged.

Merlin2021
Oct 2, 2010.
Replaced filter but that was not the issue. Replaced Fuel Pressure regulator (easy to do) and this solved most of the problem. I do believe the Fuel Pump is getting lazy and will need to be replace soon. But for now most of the problem went away.
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Tiny
Zue
Oct 28, 2010.
Ok We will be watching for any more on this!

Merlin2021
Oct 31, 2010.

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