2000 Ford Taurus wagon, **FLEX FUEL** V-6 engine running on regular E10. Began stalling intermittently. Would run rough for 30-60 seconds or so and then die, both while driving and while idling. Would restart just fine. Began happening more and more frequently and threw a Check Engine code (but I don't know what it was, repair shop says they “lost it”.) Then one morning it wouldn't start (mild Oregon climate ~55F overnight). Had it towed to an independent repair shop. They read the code and measured fuel pressure at the fuel pressure test port (on the very far end of the fuel injection rail from the gas tank) at 3psi. They diagnosed a bad fuel pump and replaced. Told me it was ready to pick up. It had been sitting out overnight. When I picked it up, it wouldn't start. With lots of cranking it finally started but ran extremely rich. Strong smell of raw gas out the exhaust and clouds of fumes (not burned oil, just unburned, rich exhaust). Gave it back to the shop. They read code P0191 and diagnosed a bad fuel flow sensor (device right at the beginning of the fuel injection rail) and replaced, but it didn't affect the problem. It will still sometimes have trouble starting and run very rich when starting from cold (cold = 55F). Without touching the throttle, engine can be shut off and started again and it will be just fine. Shop doesn't know how to proceed. I walked through with them their diagnosis of the bad flow sensor. Upstream of the flow sensor is an oval-shaped metal enclosure with fuel lines going in and out, and an electrical connection. They didn't know what this device does (neither do I). I suspect it might be the electronic fuel pressure regulator.
It is unlikely that there would be two bad components at the same time in the fuel delivery system. I suspect that the bad fuel pump was a misdiagnosis, and the bad flow sensor is obviously a bad diagnosis. There are two TSBs that might be pertinent – TSB14187 & TSB14041. But I don't understand completely the flex fuel system. What controls the fuel pressure to the fuel injection rail? What device senses the ethanol concentration of the fuel system? What is that oval box in the fuel line? What does the engine change in response to the ethanol concentration? What could be the true problem here that would fix the car?
Apart from the P0191, was any other trouble codes retrived? Seems there are a lot of unsolved problems for the flex fuel system
October, 31, 2012 AT 5:57 PM
The automotive forum link was interesting it shows that flex fuel issues can be very hard to troubleshoot. But nobody there was getting a P0191 code. That code was read by the repair shop; they didn t mention any other codes along with it.
What is the description that goes with a P0191 code?
I know what basic elements need to be in the fuel supply system, but not what order they are in the Taurus. Do you guys have access to the vehicle manuals? Can you tell me how the components of the fuel system are laid out (what components, in what order, starting at the fuel pump and ending at the fuel injector)?
October, 31, 2012 AT 6:23 PM
We do have access to and Ford websites for such information but problem is the description of the system is rather vague and principles of operations are not very comprehensive.
Without any specific criteria it would be almost impossible to get information as the amount is vast so whatever information that you require, let me know so I can search for them. I will see what I can get about the principles of operations.
You mentioned the first mechanic lost it so I do not know if the trouble codes then was the same P0191 or it could have been others.
P0191 - Fuel Rail Pressure (FRP) sensor circuit performance. The test procedures are below.
NOTE: On CNG models, if vehicle is a no-start, go to TEST HB
16) KOEO/KOER DTC P0191
DTC P0191 indicates FRP voltage signal is more than self-test maximum.
Possible causes for this fault are: High Fuel Pressure
Low Fuel Pressure
Excessive Resistance In Circuit
Faulty FRP Sensor
Low Or No Fuel
Turn ignition switch to ON position. Ensure vehicle has at 1/8 tank of fuel. Turn
ignition switch to OFF position. Release fuel pressure. Connect pressure gauge
to Schrader valve. With engine running, check fuel pressure. Fuel pressure
should be within specification. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to TEST HB (natural gas vehicles) or TEST HC (all other models).
17) DTC P0191, P1168 & P1169: Check FRP PID Fuel Pressure
Turn ignition switch to ON position. Using scan tool, select FRP PID from PID/DATA MONITOR & RECORD menu. If PID psi reading is not within 10 psi of fuel pressure gauge psi reading in step 16), go to next step (natural gas vehicles) or step 19) (all other models). If PID psi reading is within 10 psi, proceed as follows: If DTC P1168 or DTC P1169 is not present, repeat QUICK TEST.
If DTC P1168 or DTC P1169 is present, clear DTCs. Road test vehicle 3-5 minutes at a steady speed. Stop vehicle and check for Continuous Memory DTCs. If DTC P1168 or DTC P1169 is present, go to next step.
18) Check Fuel Rail Solenoid
Using scan tool, access OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. While observing fuel rail solenoid, cycle output on and off several times. If solenoid clicking can be heard or felt, exit output test mode and go to next step. If no solenoid clicking can be heard or felt, go to step 22.
19) Measure VREF Voltage
Disconnect FRP sensor connector. Turn ignition switch to ON position. Measure
voltage between VREF terminal and SIG RTN terminal at FRP sensor harness
connector. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts,
reconnect sensor and go to TEST C.
20) Check FRP Circuit For Excessive Resistance
Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect
connector for loose, damaged or corroded terminals. Repair as necessary.
Measure resistance between FRP terminal at FRP sensor harness connector and
PCM connector terminal C40 (LS) or terminal No. 63 (all other models). Measure resistance between SIG RTN terminal at FRP sensor harness connector
and PCM connector terminal No. 91 (SIG RTN). Measure resistance between
VREF terminal at FRP sensor harness connector and PCM connector terminal
C20 (LS) or terminal No. 90 (all other models). If all resistance readings are less
than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair
21) Monitor FRP Circuit With Scan Tool
Turn ignition switch to ON position. Using scan tool, select FRP V PID from PID/DATA MONITOR & RECORD menu. If PID voltage is less than.2 volt (natural gas vehicles) or more than 4.8 volts (all other models), replace FRP sensor. If PID voltage is not as specified, replace PCM. Program PCM.
NOTE: When in output test mode, voltage measurement must be made within 7 seconds of activating test mode.
22) Check Voltage At Fuel Rail Solenoid
Disconnect fuel rail solenoid connector. Using scan tool, access OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Turn all outputs ON. Measure voltage between VPWR circuit terminal (Pink/Black wire) at fuel rail solenoid harness connector and negative battery terminal. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in VPWR circuit.
23) Check Ground Circuit
Measure resistance between ground circuit terminals at fuel rail solenoid harness
connector and negative battery terminal. If resistance is less than 5 ohms, replace
fuel rail solenoid. If resistance is 5 ohms or more, repair open circuit.
24) Check VREF Voltage To FRP Sensor
Disconnect FRP sensor connector. Turn ignition switch to ON position. Measure voltage between VREF and SIG RTN circuit terminals at FRP sensor harness connector. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, VREF is out of range. Go to TEST C.
25) Check For Shorted FRP Signal
Disconnect scan tool from Data Link Connector (DLC). Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM harness connector FRP and SIG RTN terminals, between PCM harness connector FRP and VREF terminals, and between PCM harness connector FRP terminal and battery negative terminal. If all resistance measurements are more than 10 k/ohms, replace PCM. Program PCM. If any resistance measurement is 10 k/ohms or less, repair short in affected circuit.