Low end knocking noise; 220K miles;

How many miles on it? I have similar engine, and when oil is low, the timing chain tension system doesn't. At 120000 miles, I need to replace sparkplugs. I understand you can get the same sound when it needs new plugs... It's a pain to do.

4.6s are bad for timing chain knock upon first starting too when enough miles are on car.

could be a big end or main bearing but there are a few simple checks that can be done first
1--have the oil pressure checked using a mechanical gauge
if there is a bad bearing there will be low pressure at idle
2 --check the exhaust for smoke under load
if there is a bad bearing , the escaping oil will overload the oil ring and produce smoke
( if smoke comes after idling at lights and on taking off that is valve stem seals)
3--- run the fault codes and check for knock sensor problems
the noise could be detonation under load from lean fuel mixture or incorrect timing
4---check the ignition timing
5-- run the engine when it is knocking and remove a plug wire and see if the knocking stops
bearings will stop knocking if there is no combustion to place load on the crankshaft
That will also indicate which big end you have to check if you have to pull the sump
Too far advanced will cause the pistons to slap the cylinder walls hard for too far advanced ignition
you statement that the noise goes after 40 indicates that it is not a bearing as the high the rpm the louder the noise
taking the foot off the pedal indicates detonation
lastly if all the checks prove good , you could always have the sump removed and check each big end and main individually for damage
sometimes a failing cam chain if fitted ( no motor identified) will knock as the chain hits the timing cover

Yes It could be the timing belt because as your car ages and the belt gets worn it starts to stretch. If your timing belt stretches enough your car will come out of time and that will cause a peck or knock. Another thing that you may look into if you have not had a tune up recently is spark plugs and wires. If you have worn plugs or wires it can also cause this to happen on occasion. I hope this helps you out.

Hi quintincoetz,

If your noise is a ratlling noise, more like a chain top end noise, then I would recommend first checking your oil level and condition. If the oil level is ok, you can remove the oil cap while the engine is running and look for oil lubrication on the valve train. It will probably splatter out a little. The most common cause of the noise is a failing timing chain tensioner. It allows the chain to have too much slack and slap against the guild rails. The tensioner is not too hard to replace and not very expensive either. If you have more than 100k miles, it is recommended to replace anyways. If your noise is more low pitched and more like a knock, I would recommend having a technician look at further.

No if the oil light has flickered you have oil pressure loss some time just belive the sensor do help us out. lifter do not cause oil pressure loss pressure is built in the rotation of the crankshaft. The knock under the plenum will point you to that cylinder that is affected, (main bearing) as for a 1995 the injectors can only cause a misfire but no knocking noise,will they honor the warranty

The knocking or ticking is going to determine if it is in the top end, lifters, push-rod or rocker arm issue or the bottom end that would include pistons or bearings.
If it is a ticking noise, it will more than likely be a valve train issue.
If a knocking noise, piston or crankshaft related problem.

Attached is a web site that you can listen to a piston slap which is a known issue for your 4.3.
Listen to the noise and see if it sounds similar to your problem. A piston slap will generally sound as though it is coming from the central area of the engine.
Listen to the recording and let me know.
Regards,

do u have a OBD 1 scan tool? try and find one on ebay for your car, I sold mine some time back, was $400 new got $50 for it, but I fixed allot of problems like yours because it allowed me to look at real time engine data going to and out of the engine control computer (ECM)

maybe its low on oil