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Old 10-27-2011, 06:50 PM   #1 (permalink)
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Default P0191; Fuel Pump Replacement

I figured I should write up my experience in case it is helpful to anyone else.

A month ago after a 200 mile hwy drive I shut my 03 DOHC with 93K miles off for five minutes. Upon restart it idled poorly and died. Several attempts to restart had the engine idling quite poorly. I feathered the gas and was finally able to get going. Then the usual smooth running engine was back; well at least for about another month and 300 miles.

After refueling it drove 100 ft and died. Same rough engine. Cranking it sounded like it wanted to catch but it didn't. Let it sit for 90 minutes. Started and ran perfectly. Next day it stalled out twice after warm starts. Hook up my OBD reader, P0191 was pending. My OBD reader can read real time data so I charted fuel pressure. Normally around 40 PSI. Then upon the next stall it dropped, 24, 18, 16, car stalled. I figured it is my fuel pump going bad.

Rationale:

- I don't think it was the FPM, Fuel Pressure Module that caused the pending P0191 fuel pressure out of range code, since when the car ran well it read around 40 PSI and only read low when the car actually was dying. Seemed to be doing its job.

- Fuel system relay? No, it would have put the FPDM, Fuel Pump Driver Module offline throwing a completely different code.

- FPDM? Maybe, but the FPDM reports a health signal back to the PCM and the PCM would have thrown the FPDM offline code. I could have put a scope on the pump to see if the FPDM was giving the fuel pump full PWM voltage when the car was dying but that seemed really hard to do while the car stalls out in traffic.

- Clogged fuel filter? No, changed it 2k miles ago and if it was clogged I wouldn't be able to get to full RPM and highway speeds, which I could do.

- Bad ground, faulty connector. Sure but less likely given the above.

- I could have put my fuel pump guage on the car but alas, Ford decided not to put a Schrader valve on the fuel rail on Gen IV. Tapping into the fuel filter was an option but I passed on it. Lazy?

Now of course I had a full fuel tank. I removed the back seat and disconnected the fuel pump wiring from the FPDM. I placed a 2 gal gas can under the car and directed the fuel filter's output into the can. I applied 12V to the fuel pump and drained the tank, 2 gals at a time. Watching the pump work didn't give me a lot of confidence that it was at fault but then again it didn't have to build any pressure, just pump into free air. So I removed the tank and replaced the pump with a Motorcraft pump. Really wasn't hard at all, I was surprised. Put it all back together and it all seems fine. No codes pending, runs well, lots of starts and stops, about 75 miles into it. I will report back should it fail again (meaning I mis-diagnosed it) but for now I'm cautiously optimistic the issue is fixed.

Words of caution:

- do the repair outside. I started in my garage with the double door open and was quickly overwhelmed by the fumes. On the driveway no issues. It helped that it was a breezy day.

- if you hot wire the pump to drain the tank make sure your connections are tight so there won't be any sparks. I plugged my battery charger in and out on a long extension cord well away from the gas tank. Even when the flow comes to a light trickle or stops there will be gas left in the tank.

- have a second person to raise and lower the rolling jack under the tank while you guide the tank in and out. I used a piece of wood and a towel under the tank so it would slide on the jack easily as I found its center of gravity. Piece of cake really.

- clean the top of the FP before you remove it. I used a can of compressed air and some rags.

- use a BRASS punch to remove the fuel pump's retaining ring. We don't need any sparks here. When trying to reinstall the ring I had a hard time to turn it using only the punch. So I attached two vise grip pliers to the ring at 12 and 6 o'clock and had someone slightly pulling on them as to tighten the ring and one hit of the brass punch turned and locked the ring in place, easy.

I hope this helps.
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Old 10-28-2011, 07:46 AM   #2 (permalink)
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^^^^^ Very good info, and very good diagnostics! I am betting you are correct, and your pump was dieing.

How many miles on the original pump?
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Old 10-28-2011, 09:31 AM   #3 (permalink)
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Iirc, you can retrieve pressure reading(s) on valveless fuel rails with a scan tool from the fuel rail pressure sensor. My code book defines po191: fuel rail pressure sensor circuit range/performance, which i suppose a failing pump could trigger? Congrats on the fix.
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Old 10-28-2011, 09:45 AM   #4 (permalink)
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^^^^^ Thats the problem with the 191 code..... it is either from a failing pressure sensor or a failing pump. I suppose it could be possible to remove the sensor, but leave it electrically connected and apply a known pressure of, say, 40 psi to it with shop air and see if it reads right via a scan tool to 100% eliminate the sensor as the problem. This would be EASY to do with a standard fuel pressure gauge if Ford hadnt cheaped out and saved $.50 per car by not including a schraeder valve on the rail like they had since the early 80s on cars with mechanical/vacuum FPRs.
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Old 10-29-2011, 09:19 AM   #5 (permalink)
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Originally Posted by Jeff K View Post
^^^^^ Very good info, and very good diagnostics! I am betting you are correct, and your pump was dieing.

How many miles on the original pump?
It was the original pump that died. Car had about 93.5 miles on it. Picked it up new on Halloween 2002 so it turning 9 soon!
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Old 10-29-2011, 09:24 AM   #6 (permalink)
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Quote:
Originally Posted by sheila View Post
Iirc, you can retrieve pressure reading(s) on valveless fuel rails with a scan tool from the fuel rail pressure sensor. My code book defines po191: fuel rail pressure sensor circuit range/performance, which i suppose a failing pump could trigger? Congrats on the fix.
Yes, that is how I captured the fuel rail pressure, via an OBD scan tool. I use the Actron CP9580 OBD reader because I found a used one locally on Craigslist. I like it because it can graph a PID (like fuel pressure) in real time while you drive. When I changed my O2 sensors a while back I could see my long term fuel trim values slowly coming back to near 0-2%.
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Old 10-29-2011, 09:29 AM   #7 (permalink)
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Quote:
Originally Posted by Jeff K View Post
^^^^^ Thats the problem with the 191 code..... it is either from a failing pressure sensor or a failing pump. I suppose it could be possible to remove the sensor, but leave it electrically connected and apply a known pressure of, say, 40 psi to it with shop air and see if it reads right via a scan tool to 100% eliminate the sensor as the problem. This would be EASY to do with a standard fuel pressure gauge if Ford hadnt cheaped out and saved $.50 per car by not including a schraeder valve on the rail like they had since the early 80s on cars with mechanical/vacuum FPRs.
I scoured the fuel rail looking for a Schrader valve and was very disappointed to not find one. I'm going to guess this a false cost savings for Ford. As vehicles come into the shop under factory warranty with driveability complaints, one quick fuel pressure gauge connection rules out the fuel delivery system up to the injectors in one minute rather than the tapping into the fuel filter. Ford pays that labor to save a few cents on a Schrader valve.
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Old 10-29-2011, 10:01 AM   #8 (permalink)
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Riddle me this, how would you retro fit a Schraeder valve into a system?? Would that be possible with a fuel rail adaption for it, or put a Gen3 fuel rail on? This would be for a Vulcan. Just curious if that is even a plausible case? Have one on my 96 Sable starring at me.
Thnxs stan
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Old 10-29-2011, 11:36 AM   #9 (permalink)
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Quote:
Originally Posted by scn101 View Post
I scoured the fuel rail looking for a Schrader valve and was very disappointed to not find one. I'm going to guess this a false cost savings for Ford. As vehicles come into the shop under factory warranty with driveability complaints, one quick fuel pressure gauge connection rules out the fuel delivery system up to the injectors in one minute rather than the tapping into the fuel filter. Ford pays that labor to save a few cents on a Schrader valve.
The car's can read the pressure. No need for a manual pressure check.
And the onboard system can read it while you drive.

For removing fuel pressure to do filter and such, just remove the two screws on the sensor and let the excess pressure out. I just did that on my '03.

-chart-
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Old 10-31-2011, 02:53 PM   #10 (permalink)
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Quote:
Originally Posted by chartmaker View Post
The car's can read the pressure. No need for a manual pressure check.
And the onboard system can read it while you drive.

For removing fuel pressure to do filter and such, just remove the two screws on the sensor and let the excess pressure out. I just did that on my '03.

-chart-
I was able to read the OBD FRP fuel pressure real time while I drove. But to rule out a pressure sensor issue I would have liked to verify the reading with a manual fuel pressure gauge (that I have) but without the Schrader valve connection I passed on this verification as tapping into fuel filter on the underside of the car was just too cumbersome. I took the FRP sensor reading as accurate.
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