Recently I have been having intermittent stalling issues. The last time it happened, I listened for the fuel pump, and it didn't come on when I first turned the ignition switch. When I tested the leads to the pump, with the key on, it would read just under 12 volts. 11.6 to be exact. And then at about 15-20 seconds it would drop to 6 volts.
What I found odd, was that with the key off, it reads .5 volts. Not sure what to make of that.
I also bench tested the pump, and when I applied 12 volts to it, it ran as it was buzzing for sure. I went further by putting a hose on the intake into a jar of diesel, it did not pump out the fuel. I even primed the intake hose, filling it full, and the pump still did not flow fuel.
Not sure where to go from here. Any ideas where to look?

 

Not sure about the odd voltage readings, but I'm pretty sure that pump is toast.

OEM baby!

 

Bosch pump arrives tomorrow!

 

Could be a bad pump but what voltage does it show while engine running? It is programmed to prime itself for 20 seconds prior to engine cranking and then will shut itself off, so that's normal. (There is no need to wait longer than 20 seconds with the key on to crank the engine anyway if the glow plug system is working right...I used to do that but realized it was probably bad for the injectors to start the engine without fuel pressure and quit doing that.)

Does the truck intermittently lose power and stall out on you completely while going down the road as if it ran out of fuel? I had this issue when I first owned my truck and eventually traced it to a faulty PCM that needed rebuilt. (Dieseltechchattanooga does this for around $500). What happens is the truck will run without the pump on whatever is in the fuel bowl and then that's it. Mine would idle with no fuel pump but give it any throttle and no-go.

You can put a new OEM pump in for around $100...no harm there, but you might put the old one back in and do some more troubleshooting. You can get some test leads with alligator clips on the end wired to a rocker switch and run power to the pump directly off the driver side battery. (run the rocker switch along the fender line into the cab). This bypasses the rest of the circuit and tells you if the pump is the problem or not. I even drove mine around like this for quite some time before I figured out what the real problem was, and it was fine as long as I either flipped the switch off or disconnected the wire from the battery when I shut the truck off.

 

The last time out, it lost power for about 15 seconds before completely stalling. After about 10 minutes, I was able to start it again to get it home, but within a few minutes it began losing power again and did the same thing just as I pulled into the driveway. That's when I noticed the fuel pump wasn't running when I keyed on.

 

Could be the PCM then, but put the new pump in and see what happens. If doesn’t prime for 20 seconds as it should that is a clue it might be the PCM. if the pump fires right up and runs while hotwired to the battery the pump is fine, it’s just not getting power from its usual circuit. PCMs are not very good at self-diagnosing themselves as faulty when they’re faulty, but I believe you can monitor the fuel pump through Forscan on a laptop while the engine is running. it should always be “on” when the motor is running and for the first 20 seconds of key-on, after which it should default to “off”. Any deviation from that behavior is another diagnostic clue.

 

More than 20 seconds of GPs on is a good idea in subzero temps.

OP did hotwire the pump with buzzing sound and it did not pumped fuel so pump needs to be swapped.

How many miles in that pump?

 

That's my current plan. My concern being why I'm getting .5 volts at the pump, key off. You could be right about the PCM.

Correct, sir. Even when I filled the intake hose of the pump, held it uphill from the output end, there was no flow whatsoever while it was running. Less than 20k miles on this Bosch pump.

 

Have a fuel pressure gauge? Hutch and Harpoon mods in the fuel tank?

I ask since the pump died with such low miles. Maybe it was starving for fuel leading to extra wear.

 

No fuel pressure gauge, and yes, I've done the fuel tank mods. I was having a difficult time believing it was the pump until I bench tested it. Also found it odd about the .5 volts at the pump wiring key off.

Regardless, I installed the new pump, and thus far it's acting normal and running fine. I took it on a hard 5 mile run after letting it idle for 10 minutes, checking for leaks and such. I checked the fuel pump voltage again, and besides being normal, there's no voltage now at key off. Weird. I plan to take it for a much longer run tomorrow. So far, so good. Fingers crossed.

 

Sounds like ya got it beat! Congrats!

 

We have seen faulty electrical components do some weird things. The voltage readings you were logging with the ignition off are definitely unexpected, but not unbelievable at all.

Good to hear you figured it out and I hope this one lasts 100,000 miles.

 

Had same problem, on way to daughters. Even having the fp gauge(never thought to look&#128540, I had no power. Pulled off freeway and began looking truck over. Convinced myself that, there was no way I was gunna make it to Vegas. So, headed back. That's when I noticed my fp gauge...prior to hitn the rolling hills out of Barstow, I "had" power but, once a slight incline, noticed the gauge slip'n..pulled over, let the truck gain pressure and off I went...a hour drive home, normally..turned into a 3hr tour😁...
....got home, ripped pump out and noticed what looked like rocks/crystals on inlet side of pump. I even had already did the hutch mod years prior...inline wiz filter too...anywho, new pump/filter and all's been swell

 

Thanks and yes, the key off voltage really threw me. Brandons comment about the PCM had me thinking perhaps something is wrong with it. One thing I didn't mention was while I was waiting for the fuel pump to arrive, I decided to disconnect and load test my batteries. (4 year old Motorcrafts). They read a bit on the low side. I checked the cells and they were low by just shy of a quarter inch, so I topped up with distilled water and hooked up my charger for a few hours until the pump got here. When I checked the voltage readings after I installed the pump and went on a test run, was when I noticed the key off voltage was back to zero. Could the PCM have rebooted after I disconnected the batteries, or is that even possible?

 

I think it was @udsuth78 that was saying recently he had good experiences with "resetting" the PCM by removing power, but I don't have any experience or knowledge of that working. We have seen low battery voltage cause some strange symptoms as well, but I don't recall this one.

I am glad you got it sorted out without going on a wild gremlin chase, those can be tiresome and expensive.