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.
- 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.
? 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.