I was chaperoning a high school field trip today. We had chartered a couple of typical commercial busses. Typically, when something like this happens, the bus drivers are either very good, friendly, and helpful, or the bus company sends someone along to see that everything goes smoothly. This time, none of that happened.
But here’s the GQ. As we were approaching home, the bus began losing power, especially on the hills. I thought we had some real engine problems, but the guy just said we were running low on gas. I don’t think he was deliberately slowing down, but I can’t be sure. Anyway, we pulled off at an exit that fortunately had diesel, and filled up. The bus ran fine after that.
So, how does a bus that’s low on fuel lose power gradually ( I mean, over a period of about 10 minutes)? I would think if we were out - we’d be fine one second, and coasting the next. Any explanation?
(I think it’s unprofessional, and frankly inexcusable to take people’s money, load a bus with 60 or so folks, and then - oops! we ran out of gas! )
Sounds like the bus has a faulty fuel pump. When the tank is full the weight of the diesel helps push it to the injectors. As the tank empties, pressure decreases, and the engine slows.
At least the driver knew what was up. However, the fact that he knew indicates that this is an ongoing issue, and reflects poorly on the bus company…
While lacking an explanation for the symptoms related by the OP, some responses are faulty. Diesel injection pumps are of the positive displacement variety, and as such do not take advantage of head pressure, as does a centrifugal pump.
Perhaps the fuel pick-up in the tank was starting to get clogged with crud that precipitates out of diesel and other heavy fuel oils, thus the engine slowed down due to fuel starvation.
When the bus fueled up, perhaps the engine was turned off and the crud dropped off the pick-up filter/screen, or some automatic back-flush procedure could have purged the pick-up.