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Old 08-13-2012, 10:26 AM   #1
Prariefocus
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SOHC Fuel System help

Hi guys, new to the forum. I purchased a 2001 SOHC manual SE for my daughter that has a fuel delivery issue. Itís throwing a P1237 code, which I know is the secondary fuel pump circuit. The main symptom is that the fuel pump does not cut off after priming. The car runs fine, but I have the code. I have checked all the wiring and the ground from the FPDM to the pump (although I have not found a schematic, which I would really like to have). I have replaced the pump, and now replaced the FPDM. When the pump is running, it will stop if I disconnect the inertia switch. SoÖ Iím thinking now that there is nothing left but the ECU. Any thoughts or further troubleshooting advice?
Thanks! Brent


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Old 08-13-2012, 04:00 PM   #2
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Oh, and I forgot to mention, I replaced the fuel filter.
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Old 08-13-2012, 09:46 PM   #3
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Sure the fuel pump install was OK? P1237 usually indicates a fuel pump problem.
Since it fails to stop priming (I assume - your description "fuel pump does not cut off after priming" is a bit confusing), you might want to investigate the fuel rail pressure sensor.

P1237 - Fuel Pump Secondary Circuit Malfunction
Indicates that the FPDM has detected a fuel pump secondary circuit fault. The FPDM will send a message to the PCM through the FPM circuit, indicating that this failure has been detected. The PCM will set the DTC when the message is received.
Causes:
Open or shorted FP PWR circuit
Open FP RTN circuit to FPDM
Open or shorted circuit in the fuel pump
Locked fuel pump rotor
Damaged FPDM
The FPDM sends a 75% duty cycle (750 msec ON, 250 msec OFF) through the FPM circuit to the PCM while the fault is being detected by the FPDM. If the fault is no longer detected, the PCM will return to sending an "all OK" (50% duty cycle) message to the PCM. The PCM will keep P1237 stored in Continuous Memory.
The FPDM controls pump speed by supplying a "variable" ground on the RTN circuit.

2000 model year wiring
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Old 08-13-2012, 09:59 PM   #4
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Yes, correct, fuel pump does not stop "priming". It runs all the time, from the time you turn the switch to run, until you turn it off. I actually replaced the fuel sensor on the left end of the rail although it was with one off of a wreck, so I don't really know its condition. Is there a way to test the sensor? What would one expect to happen if it were unplugged while the engine was running?
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Old 08-13-2012, 10:01 PM   #5
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Oh, and thanks for the schematic!
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Old 08-13-2012, 10:23 PM   #6
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I ran across this other posting of yours, BC, which I think is on to my problem... t=243855http://www.focusfanatics.com/forum/showthread.php?t=243855
Is the fuel pump monitor (FPM) a separate device, or incorporated into the PCM ( and are PCM and ECU synonymous). Does the command to turn on or off the pump originate from the PCM as a result of the pressure sensor on the rail?
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Old 08-13-2012, 11:06 PM   #7
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Quote:
Originally Posted by Prariefocus View Post
Is the fuel pump monitor (FPM) a separate device, or incorporated into the PCM
I believe it refers to the fuel rail pressure sensor/PCM combination since it's measuring the ultimate result of the fuel pump output. Not sure though, since the terminology varies. The pressure sensor would close the "feedback loop" though; it feeds into the PCM.

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Originally Posted by Prariefocus View Post
( and are PCM and ECU synonymous).
Yes, Powertrain Control Module and Electronic Control Unit

Quote:
Originally Posted by Prariefocus View Post
Does the command to turn on or off the pump originate from the PCM as a result of the pressure sensor on the rail?
Yes. The grn/black and grn/org wires to the FPDM in the schematic originate from the PCM.

I'm not sure the other post is relevant given that you have a specific and different DTC code.
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Old 08-14-2012, 08:12 AM   #8
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Quote:
I'm not sure the other post is relevant given that you have a specific and different DTC code.
I see your point, but the P1237 code doesn't seem to be related to the pump not turning off, so I was just thinking outside the box a little to try to find a solution as to why my pump is not cutting off. Everything I've read indicates that it should run for about 2 seconds and the cut off until the engine starts when it will call for more pressure, I assume because the pressure sensor sees a drop.

I've also seen some diagrams that indicate there may be a fuel [I]tank[I] pressure sensor. It must be outside this loop if it's present on my car.
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Old 08-14-2012, 09:25 PM   #9
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Quote:
Originally Posted by Prariefocus View Post
Everything I've read indicates that it should run for about 2 seconds and the cut off until the engine starts when it will call for more pressure, I assume because the pressure sensor sees a drop.
That's the way mine works. So logically:
1) The pump is still running because the PCM is not detecting any pressure change via the sensor
2) The pressure change is being detected but the FPDM or pump is not responding to the "stop" command from the PCM
Since the DTC is fairly specific, I'm going to suggest the pump isn't doing what the FPDM is telling it to do. Since the car runs normally (right?), it might be something as simple as a bad or intermittent ground.
Also, you've cleared this code before and it's reoccurring, correct? In other words, it's not a "leftover" from the previous pump/FPDM work?
Finally, you don't have a means of logging fuel pump pressure do you, such as a scanner? Or I think the SOHC has a Schrader valve fitting on the fuel rail where you can monitor pressures. (Not sure about; that I have a Zetec.)
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Old 08-14-2012, 11:23 PM   #10
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Quote:
Also, you've cleared this code before and it's reoccurring, correct? In other words, it's not a "leftover" from the previous pump/FPDM work?
Yes, I've cleared the code and it recurs.
Quote:
Since the car runs normally (right?), it might be something as simple as a bad or intermittent ground.
Yes, it seems to run great except for not cutting off and CEL. I have removed the ground connection under the back seat next to the pump and FPDM and cleaned well with a wire brush and reconnected, ensuring a clean and tight ground. Are there other grounding points to be concerned about?
Quote:
Since the DTC is fairly specific, I'm going to suggest the pump isn't doing what the FPDM is telling it to do.
Well, I thought of this also. But the pump is simply a dc motor with two leads connected. If I have read and understood the info correctly, the black/ white wire is the ground/return that is duty cycle modulated to regulate its speed and thereby the system pressure. I assume the green/orange wire is just 12 v. I have physically checked all wiring between FPDM and pump. Although there are several wires to the fuel pump connector, only four connections on the mating receptacle are populated, two to the fuel level sensor, and two to the pump motor. These are connected back to the FPDM. I metered them out to be certain.
I would like to know where/how the fuel pump relay is energized in this system. I know the troubleshooting description for this code does not point in that direction, but it just seems that the PCM could possibly not be de-energizing the relay if/when it should, if it's supposed to.
Quote:
Finally, you don't have a means of logging fuel pump pressure do you, such as a scanner? Or I think the SOHC has a Schrader valve fitting on the fuel rail where you can monitor pressures. (Not sure about; that I have a Zetec.)
No, I don't. However, I think I might be able to get ahold of one. I was considering subscribing to Alldata to get a full schematic and theory of operation. Any thoughts? Do you know how the relay is supposed to function in relation to the pressure sensor?
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