2003 Expy 5.4 with 130k. Regular maintenance done including fuel filter in September. Truck normally runs great. We were stopped at a light in traffic last Monday and it started running rough, dropped rpm and then stopped. We'd crank it, it would stumble about 400 rpm and stop. After about 5 minutes it fired up and ran perfect. It's been good all week until tonight. Same thing again, stopped at a light in traffic and goes rough then stops. After about 5 minutes, fires up and runs great. I know it's next to impossible to trouble shoot a random problem like this. It was too busy of an intersection to try to listen for the fuel pump running. Would I be out of line to just jump straight to replacing the fuel pump? To make matters worse, we were coming back from the urgent care where I got 4 stitches in my left index finger knuckle tonight, so I'm not in any hurry to drop the fuel tank in this condition. Let me know your thoughts, they're very much appreciated.

 

First off, I want to preface this post by saying that I do NOT have the 03+ Service Manual on hand to absolutely nail down the culprit on the first try, but I do have the accumulated wisdom of the entire 97-02 models at my disposal along with nearly a decade of pinning down electrical maladies on Rotaries.

I would definitely NOT jump straight to "dying fuel pump" unless it failed to respond reliably (first time, every time) when hotwired. Not sure how much of a PITA it is to access the pump's connector to test it with a spare battery, but that's where I'd begin.

Intermittent failures are often traced to a ground in poor condition. In this case, the PCM Ground. Long story short, letting it sit for 5 minutes lets the bad ground cool back down (it acts as a resistor, resistance increases with heat) so it can behave like normal. If the PCM does not have a sufficiently solid ground connection, any possible aspect it interfaces with can be skewed so you get things like misfiring (Coils are fired by Ground signal from PCM), injectors not operating (ground signal from PCM), Coolant Temp Sensor reading being off, etc.

I would like to mention that the grounds on these trucks are no different than any other car. Bare Copper ring terminals attached to mild steel sheetmetal using mild steel hardware. After 13 years, something is bound to not be fresh. All of this is in addition to the usual suspects such as plugs/coils/etc

 

I follow the logic of resistance, heat, cooling down and working again. Is there anything else that would/could/should be affected by this bad ground? Everything in the truck continues to work. Even the ignition and injectors seem to work since the engine will stumble for a few seconds when it's cranked. Does anyone know where exactly to look for this ground? This is probably something I can get to with one good hand.

 

Before changing the fuel pump I would change the fuel filter. When this issue starts pay attention to the RPM gauge. If it bounces around wildly you could be looking at failing crank sensor, ECM, or a wiring issue. If it remains steady and simply follows engine RPMs then it's more likely that you're dealing with a fuel delivery issue.

 

Tachometer follows engine RPM. The engine runs rough with the tach showing 400-600 rpm. Is there a sock type pre-filter in the tank? I remember this being an issue on old fords, like 70's time frame, where the stock would break down and clog fuel line in the tank.

 

Yes, there is a Fuel Pre-Filter Sock on the pump's inlet. Your hunch sounds rational to me. I've not personally seen one be eaten by the pump before, but it's certainly possible. More likely is that it's full of accumulated dirt. Last time I examined it on my RX7, there were small pebble-sized chunks of sediment in it.

As for the PCM Ground, this is for 97-02 but 03+ may be similar. G103 and G104 are located behind the headlights on the radiator support, G103 on the Passenger Side and G104 on the Driver's Side. G104 is also shared with the Driver's headlight (kind of obvious lol), the Fuel Pump, all of the relay coil grounds for everything in the relay box and a few other things.
G101 is the PCM Ground, found on the firewall between the Cowl panel and Starter Relay. This is shared with other engine-related items like the Mass Airflow Sensor, Cam & Crank Position Sensors' cable shielding, Knock Sensors, OBDII connector and PATS System.

The other location where the PCM is grounded at is G201, behind the driver's side kick panel. Fuel Pump is grounded here too, along with the GEM, Gauge Cluster & Airbag Diagnostic module.

 

We have a casual road trip planned for Friday, about 150 miles round trip. If I rent a fuel pump diagnostic kit from Autozone (OEM tool part number 27167), should I be able to hook this up fairly quickly and get a pressure reading if the engine stops running again? For the most part, we don't drive it for more than 5 miles between stops. I figure if it's going to happen again (for whatever reason, a bad ground, something clogging inlet) it should definitely happen on this trip.

 

Hook the fuel pump pressure gauge up and tape it to the windshield where you can see it while you are driving.

 

We delayed or casual road trip to Saturday. I pulled the main junction box last night and opened it this morning to check for a burnt fuel pump relay. I figured that's something I can visually inspect and it's known to cause random stalling. It has definitely been hot, but not burnt out like others I've seen in my research. I'm going to add some solder to the bad post and put it all together. I'm also going to source a new relay to eventually replace this one.




Lower left corner of center relay has been hot. Plastic is slightly warped.





Close up of lower left corner with warped plastic.





Close up of lower right corner, looks clean, not warped.





Underside of relay pins. The screwdriver is pointing at the lower left hand corner pin, definitely disrupted solder. The clean pin to the left is the lower right hand corner pin, nice and clean.

 

I think this will get me through.

 

Just got back from a 12 mile drive to relearn fuel trim and shift points. Had it running about 30 minutes straight which is more than our regular day to day trips. So far, so good. Now to find/order a suitable replacement relay. Also need to get a tool (solder wick or solder sucker?) to help remove solder to remove relay.

 

Ordered a $20 relay on ebay: Ford Fuel Pump relay R303 12V Replaces Omron Relay F8VF-BA

And a desoldering pump for $8 on Amazon: Vastar® Solder Sucker Desoldering Vacuum Pump

With any luck, it'll be next weekend and another 13 years/130k miles before I have to do this again

 

Casual road trip complete, 150 miles and 3 hours of drive time. No issue. We even almost ran out of gas. Since the battery was disconnected, the "miles to empty" calculation was reset and read much higher than actual. It said 5 miles to empty when we finally got gas. The truck took 26.5 gallons and I thought these had a 26 gallon tank. I think it's fairly safe to say the fuel pump isn't overheating and failing.

I think Travis S was on the right track with overheating a connection. I read in my research that the fuel pump draws 10 amps at idle, so this would be consistent with the stalling at idle waiting for a light.

Thanks guys.

 

Update/follow up...the truck ran perfect for 9 days after resoldering the bad pin. I replaced the relay yesterday in under 2 hours, start to finish. It really wasn't difficult and saved a lot of money.

 

Very nice job, and cheap too! Rep points to you.