问：什么是在发出噪音？
My 2007 Ford F-150 (5.4L Triton, automatic, 120k miles) was making a loud clingy noise after it had warmed up. If I turned it off then back on, the noise stopped. I was told by a mechanic it was the cam phasers and it was throwing off the timing, so I paid to have them fixed. The truck ran ok for a few days and then the same noise started again. I took it back and the mechanic said oil was not getting through the engine properly and the phasers were bad. They again replace the phasers, oil lines, etc. and it still knocks at startup. If I give it a jolt of acceleration, it stops for a bit but on the next stop it happens again. All the mechanics I talk to are at a loss. What can be done to fix this?
Your description of engine knocking at idle with your 2007 Ford F-150 5.4 Triton engine is a common complaint for owners of this engine. I recommend you have a certified mechanic, like one from YourMechanic, do some preliminary checks to help isolate your problem. This complaint has to be isolated to properly diagnose it. The most common problems found is the oil pressure being at or above 25psi when the engine is cold, and lower than 25psi at idle when warm, due to oil getting thinner. The low oil pressure in a warm engine would cause timing issues with cam phasers and timing chain tensioner. The reason the issue seems to go away as you accelerate is that the oil pressure will increase as the engine RPM’s increase. Continued running with low oil pressure will cause internal damage to bearings, the crankshaft, camshafts and other internal components lubricated by oil. The cam phasers require proper oil pressure and oil viscosity. Ford recommends 5w20w for your engine. If you are using an oil that is too high of viscosity or of a wrong weight, this can cause not enough oil to reach critical parts and cause erratic cam phaser operation or internal wear. As long as the correct oil is being used then the problems described will only occur with low oil pressure. I have heard of recommendations of using straight 30 weight oil and that it quiets the noise on occasions. I do not recommend this practice, since it could cause wear damage due to tighter part tolerances or orifices that may not get enough oil to work correctly. When you get your oil pressure checked, if it is below 25psi at idle, I would recommend getting a certified mechanic to drop the oil pan, remove and inspect thrust bearings on crankshaft for excessive wear. If the pressure is ok, then replace the oil pump and screen. If bearings show excessive wear or damage, then a major overhaul or replacement of engine will be needed.
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