Last week, driving down the highway at 55mph, my Blazer just "shut down" and coasted to a stop. It wouldn't restart. No sound from the fuel pump. I ended up having it towed home. The next morning, it started up just fine (I didn't trust it to drive) and that afternoon, it wouldn't start again - no sound from the fuel pump. This is the 3rd fuel pump to fail in this truck in the last 6 months, and I got tired of dropping the fuel tank (2-3 hours x 2 guys to complete each time) so I converted it to an external in-line pump.

After the conversion, the truck started right up, and seemed to drive fine. (Note, the external pump is considerably louder than the in-tank one, so I can hear it well.) I drove it to work the next morning with no problems, but when I left at 5, I got to the first stoplight, and the pump got quieter and quieter until it stopped all together, and the truck died. I turned the key off and back on a few times, and tried to crank several times, (The pump relay wasn't clicking) and after about 30 seconds it started back up and drove to the next light, where it did it again. I got through the next couple lights by puting the tranny in neutral and revving the engine - then it didn't die. Next, as I rounded a corner, I began accelerating after turning, and I heard the pump stop, and it died again - this time it started back up almost right away. I swapped out the relay, and attempted to drive it to work the next morning. The first time it died the next morning, I took it back home and parked it.

A couple days ago, I decided to try bypassing the pump's electrical system, and hardwired the pump to the battery, and put a switch near the drivers seat so I could manually control the pump. That way, if the system that controls the relay was failing, it wouldn't affect the pump. I took it for a drive, and it did it again - even with it hardwired to the battery.

So, this pump normally makes a fairly high-pitch, semi-loud buzz. When the truck dies, the pump's pitch goes down, and it gets quieter until it stops all together. If I try to start it, it will start back up in 30 seconds or less. It's almost like the pressure is getting too high for it, and it finally can't turn anymore, and once the pressure relieves, it can spin up again, but this is just a theory.

Before I buy any more parts for this, I thought I'd ask. Anyone have suggestions as to what could be causing this?

 

Sounds like the fuel pressure is dropping off and the pump gets quieter. (I have one on my RV that you can only hear at idle.) it's obviously not the voltage cutting out with it wired to the battery. It might be the fuel pressure regulator in the manifold not holding pressure. Best way to diagnose is a fuel pressure gauge and a test drive to see what the pressure is doing when it dies.

 

Thanks for your advice, 1000monkeys. I didn't have a pressure tester, and they're just a little spendy, so I just put a new fuel pressure regulator in it, put everything back together and it ran great, until I took it for a drive. First stop sign, the pump went really quiet (I COULD hear it running, just very very quietly) and the truck shut down. After several seconds, it started right back up until the next stop.

So it idles fine indefinitely as long as I don't drive it, and it'll keep running fine as long as I'm driving. As soon as I stop (or slow way down) the pump goes silent and it dies. The pump is still hardwired to the battery. Anyone have any other ideas? I'm completely stumped... Thanks in advance.