I had the same problem once. I found that I had a leak in the piping from the skimmers and air was beeing sucked to the pump. Once also a Barracuda pipe got punctured and was allowing air to go to the pump.
There wont be any dirt under the sand. When you vacuum your pool you should do it on filter mode Otherwise you will lose a lot of water for nothing, this would be especially wasteful in the case of a salt water pool. Ofter having vacuumed the pool on filter mode and if the pressure gets too high backwash. after backwash rinse for a minute, then return to filter.
Yes it can. The sand is jagged and over time with the water running through it will become smooth and lose its effectiveness. Normal use change every 5 years, heavy use change every 3 years.
Fuel filter may be clogged. Replace the fuel filter.
Fuel Filter? Air Filter?
change the fuel filter
The filter may be lose if this is not the case the threads around the filter may be "stripped". Try changing the filter if this does not work I would take your vehichle to a certified mechanic.
A sand filter has laterals (plastic tubes with holes in them) in the bottom, covered with a foot or more of sand of a particular size grain. Pool water is flowed onto the top of the sand and vacuum pressure draws the water through the sand. The particles in the water are trapped in the upper level of the sand and the clean water flows through the laterals and back to the pool. As the dirt builds up on the top of the sand (the schmutzdeck) the filter actually cleans better. Once the dirt layer is thick enough to impede the flow of water, you have to remove it by backwashing. You do not want to backwash too often or you will lose the efficacy of the filter. Be sure to shut off the pump before you move the lever to backwash or you WILL crack the laterals - requiring a very expensive repair.
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Check the fuel filter and catalatic convertor.
Change the fuel filter or it may be the rev limitor that is in the computer..
Dirty fuel filter, dirty air filter, bad catalytic converter, restricted exhaust, insufficient fuel pressure.
1st step would be to change fluid and filter and see if any improvement