Fuel Starts W/ Fluid. Torque App Shows No Fuel Pressure at Rail. Help Please

Devmart

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Jun 27, 2017
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Hello everyone, looking for help to fix my 04 GT. Appreciate all replies.

Overwinter the 04 GT in the garage. Battery died and I replaced.

Theft light flashes when key not in ignition and goes away when key turned. Shows check engine light and battery icon when key turned.

Turn key, engine turns over but no start. Add a bit of starter fluid car starts and runs for 3 or 4 minutes. Black smoke out of tailpipe that eventually clears. Then car shuts off.

Using Torque app I show no pressure at fuel rail. Pulled codes and showing P0190 , P2196, P2198.

Hoping for a little insight, will car start and run on starter fluid if theft mode is active(No theft light showing when running on fluid)?
Seems to be fuel ( Guessing fuel pump) issue if above not issue. Have never tested fuel rail pressure gauge in Torque, what reading should I be seeing?

Thank you, all help appreciated.
 

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wmburns

SN Certified Technician
Aug 14, 2009
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For the 1999-2004 model year the fuel rail pressures sensor (FRPS) is a "no start" sensor. That is without a valid FRPS input, it should be expected the car will not start.

Any time a DTC calls out a "Circuit Malfunction" it means there's something sooooooo wrong with the circuit that the PCM is unable to perform any meaningful diagnosis. Think: short, open, ground fault.

The 5 volt reference circuit is critical to the operation of sensors that use 5 volts. It's quite possible that a problem at a different sensor can "bring down" the entire 5 volt reference for all/most 5 volt sensors. So don't limit your visual inspection and trouble shooting to just the FRPS.

Tell us EXACTLY how you are testing for key on voltage at the trunk mounted IFS switch. How did you confirm that the ground is good?

>>
P0190 - Fuel Rail Pressure Sensor Circuit Malfunction (FRP)
The comprehensive component monitor (CCM) monitors the FRP sensor to the PCM for VREF voltage. The test fails when the VREF voltage from the PCM drops to a voltage less than a minimum calibrated value​
  • VREF open in harness.
  • VREF open in sensor.
  • VREF open in PCM
Verify VREF voltage between 4.0 and 6.0V.​
 
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Devmart

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Jun 27, 2017
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Hello, really appreciate the help wmburns!

Per your info above, I should say that jumper cable to fuel pump was unplugged when code p1233 appeared(Does that matter?). Also when jumper cable was unplugged fuel gauge moved to totally empty and did not move on key turn. After re plugging fuel gauge moved from totally empty to over 1/4 fuel on turn key.


Made another attempt to test for power at harness at fuel pump. Ran a ground wire from the car battery to my tester. On turn of car key I show between 4.33 and 5.0 volts of power at that jumper cable near fuel tank for a few seconds at a time.

Reset inertia shutoff with a percussion and pressed red button down.
Unable to test for voltage at inertia shutoff. How should I do this? I plugged grounded test prong into cable harness that plugs into inertia switch and do not receive any reading.​
 

wmburns

SN Certified Technician
Aug 14, 2009
5,838
505
194
Houston Texas
I plugged grounded test prong into cable harness that plugs into inertia switch and do not receive any reading.
The Trunk mounted IFS is a simple on/off two prong switch. As such it does not have a built in ground. So the testing should be from one terminal of the IFS switch and a body ground. Have you actually identified the trunk mounted IFS switch?
Also when jumper cable was unplugged fuel gauge moved to totally empty and did not move on key turn. After re plugging fuel gauge moved from totally empty to over 1/4 fuel on turn key.
I don't understand why you are messing with the connector going to the fuel pump itself. And yes I think it's likely that the P1233 DTC is from unplugging the connector to the fuel pump. This breaks the communication path from the FPDM to the fuel pump itself. This causes the FPDM to report a problem to the PCM. Also note that the fuel pump is not powered with 12 volts directly. So attempting to directly measure power to the fuel pump with a VOM is not the way to go. Test for basic +12 volts at the IFS switch.

IMO you are either over thinking this or simply jumping around too much. Go back to basics. What are the key on voltage reading at the fuel rail pressure sensor (FRPS) located in the engine bay fuel rail BN/WH and GY/RD wires?

This should be the 5 volt reference. What to do next depends upon IF the 5 volt reference is present or not.

Have you done a through visual inspection of the wiring harness for water or rodent damage?
 

Devmart

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Jun 27, 2017
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Really appreciate the help on this! Thank you

Voltages are below:

5 volts red wire at fprs sensor

.05 volts to gray and red at fprs sensor

5 volts to brown and red at fprs sensor


Inertia Switch

12.3 volts at green and white wire- middle prong on ifs harness( Ifs= Inertia switch with red button push down?)

.03 volts at pink and black wire- Right side of Harness ifs harness


Car is stored in garage, a careful exam of wiring harness in engine bay shows no rodent, insect, burn, or physical damage.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,838
505
194
Houston Texas
.03 volts at pink and black wire- Right side of Harness ifs harness
^^^SMOKING gun alert!!>>> 0.03 volts at the trunk mounted IFS switch PK/BK wire PROVES that the IFS switch is not passing power.

I suspect that if you were to provide a temporary jumper wire across the IFS switch, this will improve the situation. For example, the sound of the fuel pump running at initial key on.

Bottom line. As a simple switch there must be voltage on both sides in order for the current to pass through the switch.

Note, there could be other problems with your car. But getting power to the fuel pump puts you one step closer.
 

Devmart

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Jun 27, 2017
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Great News!

Fyi, voltages were tested at harness that plugs into ifs switch(before switch)

I ran a jumper wire between grn/white and pnk/black wire at ifs wire harness.

Received no prime or noise from fuel pump.

What would next steps be to diagnose?
 

wmburns

SN Certified Technician
Aug 14, 2009
5,838
505
194
Houston Texas
We need to fall back and double check the work. I'm thinking there are some "missing" details regarding HOW some of the tests have been done.

For example. When testing the trunk IFS switch did you do the tests/measurements with the switch connected or disconnected? The requested tests need to be done with the IFS fully connected and in circuit.

Also suggest double checking your work as it would be fairly rare for the IFS switch itself to have failed.

Double check there is still key on voltage at the trunk mounted IFS. IE, that a fuse hasn't been blown from the recent work done.

Regarding the voltage tests at the FRPS, all tests need to be done using the GY/RD wire as the ground reference (not the car's frame ground).

Does your ODB2 scanner have the ability to monitor PID's? IE can you see if the fuel pressure PID changes while jumping the center signal return line to the 5 volt supply? Repeat to the signal ground. Jumping should cause the FRPS to immediately jump to max and then Min values.
 
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Devmart

New Member
Jun 27, 2017
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Wmburns,

Really appreciate all the guidance and advice on testing ifs and fprs. Per your advice above, retested at the gprs sensor and received same voltages. As you said the inertia switch rarely goes bad. Using info from an old forum post on this site, I jumped the fuel pump. No noise or action. Concluded that a bad fuel pump was the culprit.

Dropped fuel tank and installed a new fuel pump.
Problem fixed!! Also want to add that fuel pump died overwinter. Never any signs of eminent failure or intermittent operation.

Thank you Wmburns!
 
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