Initial start up of engine produces approxiametly a 60 psi oil pressure indication then drops to 10-15 psi. This is a new pump purchased form Autozone, could it be bad or is there another possible reason for the pressure drop?
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The 4.3 engine should have 20 to 30 psi at idle cold and around 50 to 60 psi running down the road. Has this engine had regular oil changes? If not the problem could be sludge build up. The oil pressure sending unit could be the problem. If in question about the sending unit install a mechanical gauge and watch the pressure.
The first stop is to measure the pressure with an external gauge. if the readings are the same, surgery is needed, I would look at the oil pressure relief valve for foreign particles.
It takes resistance to make pressure, and your decsription does not sound good. If the pressure is actually dropping, and you find no issues with the oil pump and pick up, you need to measure bearing clearances... Essentially, everywhere oil is pumped needs to be inspected...
First off its not a 351W modified. you are confusing two different blocks. its either a 351 windsor or a 351m (modified) and if it is the modified its not that bad. these engines are notorious for having low oil pressure. at idle they can be anywhere between 10 and 40. as long as you gain 10 psi per 1000 rpm its fine. and a pump doesnt drop off as it gets warm. it either works or it doesnt, oil pressure dropping off is a bottom end bearing problem
Start with the simple and replace the fuel filter. The fuel filter may have reached the end of it's life time and is dirty causing the issues you have. The worst is the fuel pump it self has gone bad and needs to be replaced, the fuel pump should be producing 62 to 65 PSI when the engine is started and should drop no more then 5 PSI when the engine is running. You can check the fuel pressure at the shredder valve with a fuel pressure gauge. Good luck and keep me posted, be glad to help get your Yukon running 100% again.
30-40 psi of oil pressure is fine for many vehicles including your GMC. I am assuming that the truck has more than 100,000 miles on it and still has the original engine in it. By rule of thumb you only need 10 psi per 1000 rpms in a typical street driven engine to give adequate oil pressure to keep the bearings from oil starvation. The oil pressure is typically higher when initial start up occurs because it is more viscous due to the temperature of the oil as the engines oil warms up the visconsity thins out and the oil flows more smoothly. The drop in oil pressure is a normal occurance. Above 45 is more than required for a daily driven street engine. I believe that the specs on that engine only list 30- 45 psi.