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2005 Mounty 4.0 persistant P0193 code

Discussion in 'Stock 2002 - 2005 Explorers' started by bronchole, January 22, 2017.

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  1. bronchole

    bronchole Driveway flexing! Elite Explorer

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    The car:
    2005 2WD 4.0 automatic with about 110K miles on it.

    The symptoms:
    Check Engine light comes back on within 20-40 miles of being reset
    P0193 code (fuel pressure sensor high)
    Poor gas millage, around 12 MPG (was about 18 MPG a year ago)
    Occasionally runs slightly rough, mainly at idle

    We ran the Mountaineer for a few months with the CEL on but I have to get a smog inspection in order to renew the registration so it became time to fix it. I replaced the fuel pressure sensor with no change to its behavior . It still throws the code within a few 10's of miles.

    I did some data logging with my OBD scanner monitoring the fuel pressure relative to manifold pressure. It shows that the fuel pressure is normally about 40PSI, dithering a couple PSI (about +/- 2 PSI). I could see the changes in PSI when I accelerated and decelerated and I could see the computer respond to the change and drive the PSI back to the desired 40 PSI. Pretty cool stuff.

    Data Logging as my wife was freeway driving for a few 10's of miles, sure enough, the PSI shot up to a dead solid 60 PSI +/-0 PSI. There was no noticeable impact to the way the motor was running. I suspect that 60 PSI is the max output of the sensor or the ECU input tops out at that level of signal. After a minute or 2 the CEL comes on with P0193 again. I clear it while we are driving down the freeway. By the time I get back to the data logging screen the PSI is back down to 40 PSI. More 10's of miles the problem repeats.

    With the engine running and the data logger running (seeing 40 PSI) I went around the engine compartment wiggling all of the harnesses I could reach. No change to PSI, no change to how the engine runs.

    Just for general interest I decided to remove the fuel pump relay while the engine is running to see how the PSI would respond. As you would expect the PSI immediately started to drop and after a second or 2 the motor stalls. Pretty predictable.

    The next test I would love to do is pull the fuel pump relay when it thinks it sees 60 PSI and see what happens. That would tell me if it was an actual 60 PSI issue or some problem with the sensor, wiring or ECU.

    Looking for any other thoughts on this.

    thanks,

    Dan
     
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  3. imp

    imp Well-Known Member

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    @bronchole
    You have pretty thoroughly gone through this. What were symptoms, code(s) while you drove with CEL ON, before you replaced the sensor? Same? Talking about the Fuel Pressure and Temperature Sensor, under the upper intake manifold, right? My experience with that: Code indicated it was faulty (different code from yours, forget now), replaced with a new sensor from NAPA, it crapped out in a month or two, same code. Replaced again, part from O'reilly. Suggests these sensors are not a foolproof thing. Others have posted about high fuel pressure, with the returnless system, where the PCM (ECU) drives Module to deliver maximum pump speed, if signal fail would otherwise kill engine, IOW, keeps the vehicle running, but at high fuel pressure, the pump is said to have a pressure relief valve which redirects the excess fuel back to tank.

    IMO, I'd go for the Module, and/or another sensor. If this all turns out to be the replacement sensor, give it hell on a vise with a 2lb. hammer! imp

    Keep in mind driving very rich a long time kills piston rings: is there any black smoke? Proly rough on cats also.
     
  4. bronchole

    bronchole Driveway flexing! Elite Explorer

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    So I got to thinking...... then I got to data logging again.

    Went for a drive with the wife.
    - Reset/clear trouble codes
    - Start data logging - Fuel PSI = 40 +/-
    - Drive 10 minutes - Fuel PSI = 40 +/-
    - Idle 30 minutes - Fuel PSI = 40 +/-
    - Drive 20 minutes - Fuel PSI = 40 +/-
    - Idle at In-and-Out drivethru, at some point a minute or 2 in to this the fuel PSI pins up to 70 PSI rock solid. Again, no noticeable change to the way it is running. Stays pinned for about 15 minutes while we finish getting food and eat it, then drops back down to 40 PSI +/-. Engine idling smooth the whole time.
    - Finish eating and drive for about another 10 minutes - Fuel PSI = 40 +/-
    - Turn around at an intersection and the fuel PSI goes back up to 70 PSI rock solid and the CEL comes on.
    - Get out and disconnect the fuel pump relay. After a second or so the engine starts to run rough, I plug it back in, engine smooth's out. I do this several times. The PSI is 70 rock solid the whole time. I even leave the relay out until it stalls, plug it in and restart the motor. 70 PSI rock solid the whole time.
    - I try clearing the codes. CEL light goes off, but still at 70 PSI rock solid.
    - Try rebooting my OBDII reader setup to see if it is some sort of glitch on it. Still 70 PSI rock solid.

    Since I caused the fuel pressure to drop significantly yet the ECU still thinks the fuel PSI is at 70 I can surmise that the fuel pump, fuel pressure relief valve, fuel filter are not part of the cause.

    That means I am left with one of the following:
    - Fuel pressure sensor: I did replace this, but maybe the replacement part was also bad. Wouldn't be the first time I got a bad part right out of the box.
    - Wiring between the fuel pressure sensor and the ECU is damaged.
    - The ECU is having problems

    Am I missing anything? Please comment what your thoughts are. I hate the idea of taking this to the dealer and getting ass raped by them.
     
  5. bronchole

    bronchole Driveway flexing! Elite Explorer

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    IMP, thanks for the reply. I have read thru a couple of your threads on the subjects related to the P0193 codes.

    Long term symptoms are poor fuel economy. May be running a little rougher than we remember, but not very rough. If it wasn't for the CEL I'd ignore the roughness. As stated in the Symptoms on my initial post, P0193 code (fuel pressure sensor high) is the code, same before and after changing the fuel pressure sensor (under the intake plenum).

    The exhaust is not stinky or black. I do not know if it is running lean though. Nearly as bad of a condition. I'd prefer to fix this rather than keep driving it at this point so we are going in the right direction.

    Given the latest test I just ran I am pretty sure that the driver module that is between the ECU and the fuel pump is not part of the fault since even when the fuel pump is not running and all of the pressure in the fuel system has been consumed by the engine running, the fuel pressure according to the ECU is still at 70 PSI.

    Keep the input coming. I am looking for an ah ha that will get me to the fix ;)
     
  6. imp

    imp Well-Known Member

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    @bronchole "Am I missing anything"

    Not much, IMO. The key part here is the damned sensor. Then the Fuel Pump Driver Module. Looking at the Wiring Schematics, I see the sensor has a variable resistor in it which is in series with the Engine Coolant Temperature (ECT) sensor. Cold engine always causes rich mixture, but that's mainly controlled by injector time I think, not fuel pressure. But, maybe......ECT output could be checked for in range or not.

    The Fuel Pump Driver Module gets it's power through the Inertia Fuel Shutoff Switch. It's circuitry gets signal from ECU, runs pump at sufficient speed to maintain pressure desired in rail. Module output feeds directly to the pump motor. I see no way the ECU could monitor the Module for failure, other than through the Pressure Sensor, but.....who knows? IMO, I'd change the sensor again, while buying it, inquire about availability of a new Module. Be glad it ain't the ABS Module, nobody sells 'em except that ass-eating dealer! imp

    PS: Failed ECT would be detected by ECU, output not within range, throws code for that.
     
  7. imp

    imp Well-Known Member

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    @bronchole
    My understanding is that the ECU defaults to running the pump at maximum voltage in the event of loss of pressure data.
    (bold) Aha (maybe). Question is what does ECU "look at" to determine the fuel pressure? Gotta be the output of the G.D. pressure sensor. See any other thing present which converts pressure to an electrical signal? I don't. Haywire pressure sensor. Faulty ECU unlikely, as I learned the hard way, final step in Ford Troubleshootiung was "Replace ECU". I did. WRONG. Now I've got 2 good ECUs which either one will only start with one frigging key!
     






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