177,000 miles, fuel pump was replaced just before I purchased it a few weeks ago. Truck has been running like new until today when it started doing this completely out of the blue. If you watch the video, the sound is not off, the tach is moving independently of the sound of the actual revs. Occasionally when doing this, the fuel gauge drops to zero. Thinking this is an electrical issue somewhere.

 

May have solved my own problem. I started thinking about what changed between the last time I drove it before I parked it and this stalling issue. Only thing I did was drive up a rolled asphalt curb a little harder than I planned (but no harder than any bump I normally take). I took off the kick panel to check the inertia switch and when I pressed on it the switch ever so slightly moved and clicked, less than a hundredth of an inch.

Restarted the truck and all seems well now. Going to replace the switch if it's that damn sensitive.

 

Ordered a new inertia switch. When I pulled the old one, I could get it to trip with just a light flick of the wrist. The new one wouldn't budge even with a good shake. Drove all day today with no issues, so I'm hoping all is back to normal.

 

I know I'm just talking to myself in this thread, but hopefully I can document my struggles so someone else can learn from the situation.

After a couple days of normal operation, the truck started acting up the same way again. This time, after angrily Googling while waiting for a tow truck, I came across info about fuel pump relays intermittently cutting out, especially when hot (like, you know, daytime temperatures in the desert). So with everything quiet, I switched the ignition from off and back to on and only heard a faint click from behind the dash. I cycled the ignition a couple of times until I heard the click become much more positive. At this point I started the truck and everything ran fine. Canceled the tow truck and drove home.

I have a new fuel pump relay I hope to install today. To try to verify the relay is the culprit, I will cut open the old one and see what kind of condition the contacts are in. I'm hoping to find corrosion, oxidation, or some other type of obvious failure point.

 

My understanding is that 2003 model did not have a stand alone "fuel pump relay" (as older models had behind the radio , located next to flasher relay).
So, I am reading your notes , please continue providing info.
Good luck,

 

Don't know if the trucks were the same, but in the 2002 Excursion all the relays were moved to a panel under the steering column.
There is a stand alone fuel pump relay it's just soldered to the bottom layer of the fuse/relay panel in this configuration.

 

After pulling the radio and finding only the flasher relay where I thought the fuel pump relay would be, I realize this truck has the integrated relay in the fuse panel as was mentioned above. The only reason I've been tap dancing around the fuel pump as the fault is that the previous owner had the fuel pump replaced just before I purchased it. He had the receipt.

Due to frustration, I bent myself and my phone to get a better look at the top of the fuel tank to see if maybe a wire got pinched during the installation of the fuel pump, only to find this:



I don't know about you, but that sure doesn't look like a few month old fuel pump to me. I'm not sure who pulled the fast one, the owner or the shop that "did" the work, but now I'm pissed. A failing fuel pump fits the symptoms better than anything else.

 

Or a failing fuel pump relay.
If the relay contacts are burned the pump will not get enough current to run properly.
You can monitor the voltage getting to the pump at the Inertia Switch.
As a test you can run 12v directly from the battery to the Inertia Switch to see if the pump runs.
Include a 20A fuse and a switch in the test line and jumper into the Inertia Switch connector.
The PK/BK wire goes to the fuel pump.
It's probably the pump, but I've read how someone changed their pump twice before figuring out the relay was bad.

 

I've got a new Delphi pump on the way. If it does turn out to be the relay, though, instead of replacing the entire fuse block with the same $300 part with the same inherent design flaw (unserviceable, undersized), what would be the harm in bypassing the factory relay and adding a standalone unit?

 

So, if I do end up bypassing the factory fuel pump relay, it looks like I'll be tapping off of fuse # 45 ignition run/start feed so that the relay will get power even when cranking. What's interesting, though, is that when probing to see how the current fuel pump relay works, it appears to trigger for about a second when you first switch the ignition to on, then it cuts out. It turns back on while cranking and continues to run until you turn the ignition back off.

Everything I know about the fuel system on this truck tells me that unused fuel just gets sent back to the tank, so why would the factory relay cut out after a second? I understand it's trying to prime up pressure for the injectors, but why doesn't it continue to run?

 

So there won't be a massive fire hazard squirting out if the engine fails to start because of a fuel leak.
It is supposed to run momentarily to pressurize the fuel rail then the pump stops until the engine is spinning a certain RPM (faster than the starter motor spins). That is the way the system is designed to work.

 

Thinking fail mode symptoms for a second.
If the PCM doesn't see the engine RPM above a certain level it won't turn the fuel pump back on.
What is the PCM using to measure RPM - crankshaft sensor?
The engine will fire for a couple of seconds with the fuel rail pressurized, but die as soon as the pressure drops off.
Can the crankshaft sensor be degraded, not throw a code, cause the engine to run a couple of seconds, then die because the PCM can't accurately read RPM?

 

I'm not saying I disagree with you since I don't have enough technical knowledge of this platform. However, with a test light I noticed the relay sending power for just a second when the key is turned to "On", then it started sending power again as soon as the key was turned to "Start". There was no delay between the key being turned and the engine coming to life.

 

I don't see where you mention if you have checked fuel pressure.

 

Yes, that is the same sequence I have seen on our cars.
I don't know the software logic behind keeping the fuel pump enabled after selection of START.
It probably does enable fuel pump power immediately at START, but waits a short time to check if all conditions are met to continue running.
I think the first condition is for PATS to be a GO before the spark plugs are fired.
In my cars the starter is not disabled by the PATS.