QuestionI have a1996 Cadillac deville with a 4.6 northstar and it is making a loud knocking noise with the car in park at idle . What could cause this problem or where should I start diagnosis
AnswerHello,
Unfortunately, logistics plays an issue here because unless at the vehicle, there are many things that can fit your complaint, but I will try.
You did not say where this knocking noise was coming from? The engine? The transmission bell housing area? The exhaust?
This could be a potential main bearing problem at the crankshaft inside the engine. Some of these Northstars had oiling issues.
I would suggest if this noise is like a solid thud coming from the bottom of the engine, you should consider having an oil pressure gauge on the engine. You should have 20-30 pounds in drive with a warm engine.
If the pressure is lower, you may have a spun main. In such an instant that oil pressure is low, the bottom end of the engine needs to be ripped down for inspection and possible replacement of the mains. However, it should be considered that the main bearing issue is the after effect of some other issue such as bad cam bearings not supplying oil to the mains.
The problem is that it is rare to find a good used engine in the junkyard because all Cadillac aluminum engine were susceptible to over heating issues and running at 225 degrees or with the hot light on causes them to start melting and blowing head gaskets.
I am only giving you a worse case scenario.
It is possible if the noise is coming from the transmission bell housing, that the torque converter bolts have become loose.
As for exhaust systems, the mufflers can fall apart internally, the noise will sound like it is comng from up front, and the vehicle can be driven doing no harm.
The problem about knocking noise on a vehicle, engine, trans or exhaust is that the noise will travel which makes it hard to diagnose and impossible over the internet!
Even if you sent me a video, it would do me no good, because I have no way of isolating the location of the knock.
You can consider what I advised here. You can take a ratchet extension and place on the oil pan to your ear, or the trans to your ear, but it takes training and experience to diagnose such noises with a stethoscope by a tech. In my older years and my hearing not that great anymore, even I would have a problem with that now.
You may want to take the car to a local service center (NOT A DEALER) and have the problem diagnosed.
A knocking noise from this type of vehicle is not common other than the oiling issue or torque converter bolts being loose.
Let me know what you find.
Good luck.
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