Problems with a vehicle's high pressure oil pump can occur for several reasons, the most common of which is long periods of time between regular maintenance work. Oil pressure can be affected by oil that has been left to sit, without being drained from the reservoir, causing hardened debris to form and create blockages. This can prevent oil from reaching the engine, and it can also cause the oil filter or the oil pump screen to stop working effectively. Too little oil pressure can have detrimental effects on vehicle performance, and over time can even cause engine failure. Determining the causes of issues with the high-pressure oil pump can be accomplished with a few specific steps.
First, examine the condition of your oil pump's hose and support bearings, which are hardware put in place to control the volume and pressure of oil picked up by the system. When bearings are tightened as recommended, oil pressure is increased. Bearings can become loose over time, due to corrosion, dirt, debris or too little oil; this is one of the most common causes of too little oil pressure. As long as the bearings are still in good condition, they can easily be tightened, with a basic mechanic's tool set. Also, look for any signs of cracking in the oil pump hose. A damaged hose needs to be replaced as soon as possible, because it can cause serious oil leakage, and more serious mechanical issues.
Make sure your vehicle's oil itself is not dirty, and/or too far below the recommended level. If so, both the oil and filter need to be changed. If excessive dirt in the oil does not seem to be the immediate problem, test the engine's oil intake, by filling the reservoir to the recommended level. Remove and check the reservoir's valve cover for excess debris, that may be blocking some of the flow to the engine. If a good deal of sludge is caked on the valve cover, most of it can be chipped off with a flat screwdriver, and cleaned up with a vacuum. Replace the cleaned valve cover, and test for increased oil pressure.
Test the Engine and Pump
Start the vehicle's engine, and pump the accelerator 1 or 2 times, while listening for any unusual rattling noises. These indicate a possible need for engine repair, if your oil pump bearings had previously been loose. With the engine still running, examine its intake valves. They should be visibly coated with oil. If not, there is not enough oil pressure. It is also recommended to use an external oil pressure gauge, to help narrow down potential problems. If there is no knocking on rattling from the engine, and you started out with a low oil level, is most likely that the oil pump itself, along with the screen, need to be removed, cleaned and replaced. If you started out with a higher oil level that quickly decreases, there could be a crack in either the hose or the crankshaft. Lastly, if the oil level starts out high and does not decrease significantly, the cause is likely a blockage in the oil sending unit.