Cadillac Repair/loud knock


I 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


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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Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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